Tumor Control Probability of Radiosurgery and Fractionated Stereotactic Radiosurgery for Brain Metastases

Upfront frameless hypofractionated gamma knife radiosurgery for large posterior Fossa metastases

The management of large metastatic brain tumors (METs), particularly those in the posterior fossa (pf-METs), is challenging. While surgery can alleviate symptoms, it carries the risk of complications such as leptomeningeal disease (LMD). Upfront hypofractionated Gamma Knife radiosurgery (hf-GKRS) has shown promise as an alternative approach for managing large METs. This study assesses the efficacy and safety of upfront hf-GKRS for treatment-naïve large pf-METs. In this retrospective, single-center study, 40 patients with 42 pf-METs received hf-GKRS from October 2017 to June 2024. Patients eligible for the study were 18 years or older, had histologically confirmed malignancy, large pf-METs (> 4 cm3), and a minimum of two follow-up MRI scans. The primary outcome was local control (LC), with secondary assessments of distant intracranial failure (DICF), intracranial progression-free survival (PFS), overall survival (OS), and toxicity. LC was achieved in 88.1% of pf-METs over a median follow-up of 6 months (mean: 13.7 months). LC rates at 6, 12, and 24 months were 95.8%, 95.8%, and 74.5%, respectively. Local failure (LF) occurred in 11.9% of cases, with a median recurrence time of 12 months. DICF was noted in 35% of patients, while no cases of LMD were reported. Intracranial PFS rates at 6, 12, and 24 months were 54.1%, 39.0%, and 16.7%, respectively, with a median PFS of 8 months. Symptomatic hydrocephalus developed in one patient (2.5%). Controlled primary tumor status (HR: 0.17, p = 0.036) was significantly associated with lower risk of death, while no other parameters were predictive of LC, DICF, or intracranial PFS. hf-GKRS demonstrates strong efficacy and safety as a primary treatment for selected, treatment-naïve large pf-METs over a relatively short follow-up duration. Further studies are warranted to refine patient selection, fractionation, and dosing strategies for this challenging population.

Postoperative stereotactic radiosurgery for intracranial solitary fibrous tumors/hemangiopericytomas: A systematic review and meta-analysis

BACKGROUND

Intracranial solitary fibrous tumors (SFTs) and hemangiopericytomas (HPCs) are infrequent neoplastic lesions characterized by hypercellularity and considerable vascularization. SFT/HPCs are associated with a considerably higher likelihood of recurrence and development of metastasis. Maximal safe resection with the goal of achieving gross total resection (GTR) is the gold-standard therapeutic option; however, it is challenging due to considerable vascularization and susceptibility to intraoperative hemorrhage concurrent with adjacency to the critical neurovascular structures. SRS has been demonstrated as an efficient adjuvant treatment option for intracranial SFT/HPCs. This meta-analysis evaluated the efficacy and safety of postoperative SRS in intracranial SFT/HPCs.

METHODS

On February 5, 2025, a comprehensive search of PubMed, Embase, Scopus, and Web of Science was conducted. Studies that evaluated SRS in intracranial SFT/HPCs and reported local tumor control (LTC), overall survival (OS), and progression-free survival (PFS) were included. The analysis was conducted in the R program.

RESULTS

Ten studies with 228 patients and 469 SFT/HPCs were included. The meta-analysis showed a pooled overall LTC rate of 68 % (95 %CI: 55 %-80 %), 1-year LTC rate of 94 % (95 %CI: 90 %-97 %), and 5-year LTC rate of 60 % (95 %CI: 42 %-76 %). The meta-analysis revealed a pooled overall OS rate of 59 % (95 %CI: 43 %-75 %), 5-year OS rate of 85 % (95 %CI: 67 %-97 %), and 10-year OS rate of 64 % (95 %CI: 25 %-95 %). In addition, The meta-analysis revealed a pooled ARE rate of 6 % (95 %CI: 3 %-9 %).

CONCLUSION

Postoperative SRS is an efficient and safe adjuvant therapeutic option for intracranial SFT/HPCs. SRS has comparative results to conventional RT with lower ARE. Further prospective multicenter studies with large sample sizes are required to validate our findings.

The role of upfront radiation therapy for brain metastases in the era of CNS-active systemic therapies: a narrative review of clinical trial design and lessons learned

PURPOSE

Systemic therapies are increasingly being considered as primary treatments for brain metastases (BM), deferring the upfront use of local treatment modalities. However, evidence to support this paradigm shift is difficult to interpret given the volume of data published and the intricacies of the outcomes reported. The objective of this narrative review is to evaluate the current evidence guiding treatment selection for BM patients by assembling and analyzing a detailed dataset of clinical trials, completed and published during the last two decades.

METHODS

Obstacles in interpreting the results of prospective systemic therapy clinical trials are detailed, including non-standardized study cohorts, inconsistent use of response assessment criteria, insufficient endpoint definition for central nervous system (CNS) efficacy, and under-reporting of previous radiotherapy. The paucity of prospective data to guide radiation therapy options is also addressed, and caveats of the available published evidence are detailed.

RESULTS

Proposed treatment and follow-up recommendations for patient with newly diagnosed BM are provided based on currently available evidence.

CONCLUSION

Prospective trials evaluating contemporary treatment paradigms and defining the respective roles of systemic and local therapies are eagerly awaited.

Suitability of a BeO-based OSLD system for end-to-end remote dosimetry tests in SRS/SRT applications

PURPOSE

The aim of this study is to evaluate the suitability of a commercially available Optically Stimulated Luminescence Dosimetry (OSLD) system for remote dosimetry end-to-end tests in Stereotactic Radiosurgery and Radiotherapy (SRS/SRT). This is achieved by performing a dose-response characterization focusing on the relevant irradiation and readout conditions, followed by dosimetry protocol development and implementation.

METHODS

The myOSLchipTM Beryllium Oxide- (BeO-) based OSLD system (RadPro, Germany) was employed throughout this study. Measurements were performed to assess element sensitivity, signal depletion, linearity (up to 16 Gy), potential beam quality (6MV and 10MV) and angular dependence, signal fading rate, and potential sensitivity changes with lifetime accumulated dose (up to 98 Gy). Correction factors and uncertainties were determined following the AAPM TG-191 recommendations. The dosimetry system and protocol were implemented in an end-to-end remote dosimetry test, considering a clinically realistic single-isocenter multiple brain metastases case. For this purpose, 17 dosimeters were placed in a head phantom involving bone-mimicking inhomogeneities.

RESULTS

A fixed depletion correction factor may not be applicable to all OSLDs. In 6MV, a sublinear dose-response behavior (up to 5%) was observed for the dose range, reader and readout parameters investigated, while an edge-on irradiation resulted in a 2.8% under-response compared to en face. OSLD sensitivity was stable up to at least 98 Gy of accumulated dose. Overall spatial and dosimetric experimental uncertainties in the end-to-end test were estimated at 0.6 mm and 3%, respectively. The local gamma index passing rate was 100%.

CONCLUSION

The evaluated OSLD system is suitable for end-to-end tests in SRS/SRT. This study can serve as an implementation guide in such applications.

Stereotactic radiosurgery for patients with brain metastases: current principles, expanding indications and opportunities for multidisciplinary care

The management of brain metastases is challenging and should ideally be coordinated through a multidisciplinary approach. Stereotactic radiosurgery (SRS) has been the cornerstone of management for most patients with oligometastatic central nervous system involvement (one to four brain metastases), and several technological and therapeutic advances over the past decade have broadened the indications for SRS to include polymetastatic central nervous system involvement (>4 brain metastases), preoperative application and fractionated SRS, as well as combinatorial approaches with targeted therapy and immune-checkpoint inhibitors. For example, improved imaging and frameless head-immobilization technologies have facilitated fractionated SRS for large brain metastases or postsurgical cavities, or lesions in proximity to organs at risk. However, these opportunities come with new challenges and questions, including the implications of tumour histology as well as the role and sequencing of concurrent systemic treatments. In this Review, we discuss these advances and associated challenges in the context of ongoing clinical trials, with insights from a global group of experts, including recommendations for current clinical practice and future investigations. The updates provided herein are meaningful for all practitioners in clinical oncology.

Current Treatment Paradigms for Advanced Melanoma with Brain Metastases

The therapeutic management of melanoma brain metastases has undergone a profound revolution during recent decades. Optimal integration of systemic therapies with local treatments seems to represent the strategy to pursue in order to maximize clinical outcomes, stressing the need for real multidisciplinary care in this setting of patients. However, the current approach in the clinics does not necessarily reflect what the current guidelines state, and several pending issues are present, from the ideal therapeutic sequence between stereotactic radiosurgery (SRS) and drug administration to the current role of surgery and whole brain radiotherapy (WBRT), all of which need to be addressed. This narrative review aims to provide practical help for navigating the current controversies, with an eye towards possible future advancements in the field, which could help to obtain a comprehensive molecular characterization of the tumor and a more personalized patient-centered therapeutic approach.

Efficacy and safety of online adaptive magnetic resonance-guided fractionated stereotactic radiotherapy for brain metastases in non-small cell lung cancer (GASTO-1075): a single-arm, phase 2 trial

Background

Brain metastases (BMs) in non-small cell lung cancer (NSCLC) are associated with poor prognosis and quality of life (QoL). This study aimed to evaluate the efficacy and safety of online adaptive MR-guided fractionated stereotactic radiotherapy (FSRT) using a 1.5 T MR-Linac in this subgroup of patients.

Methods

This single-arm phase 2 trial was conducted at Sun Yat-sen University Cancer Centre. Patients aged 18-75 years with NSCLC, 1-10 BMs, and an ECOG status of 0-1 were included. Key exclusion criteria included inability to undergo contrast-enhanced MRI and contraindications to bevacizumab. Patients received 30 Gy adaptive FSRT in 5 daily fractions under real-time MR guidance, with bevacizumab before (day 1) and after (day 21) FSRT. The primary endpoint was 1-year intracranial progression-free survival (IPFS); secondary endpoints included objective response rate (ORR), 1-year progression-free survival (PFS), 1-year overall survival (OS), treatment-related toxicities, and QoL. All enrolled patients were included in primary and safety analyses. This trial is registered with Clinicaltrials.gov, NCT04946019.

Findings

Between June 10th, 2021 and June 29th, 2023, 70 patients were assessed for eligibility and 55 patients were enrolled (median follow-up: 22.3 months). The median age was 58 years (IQR: 51-65), with 33% (18/55) female patients, and 82% (45/55) presenting with adenocarcinoma. The 1-year IPFS rate was 78.7% (95% CI, 68.2%-90.7%), with a median IPFS of 21.9 months (95% CI, 13.8-30.1 months). The 1-year PFS rate was 63.5% (95% CI: 51.8%-78.2%), and OS was 82.4% (95% CI: 72.6%-93.6%). The ORR reached 78% (95% CI: 65.0%-88.2%). Treatment-related toxicity was minimal, with only one case (2%) of grade 1 radiation necrosis. QoL improved steadily, with the Global Health Status score increasing from 65.67 ± 16.97 to 79.33 ± 8.79 at 6 months post FSRT (p < 0.0001).

Interpretation

Online adaptive FSRT using a 1.5 T MR-Linac has demonstrated effectiveness and good tolerability for BMs in patients with NSCLC. However, the relatively small sample size and short follow-up may affect result generalizability. Further randomised studies are warranted to confirm these findings and establish optimal treatment protocols.

Funding

The National Natural Science Foundation of China (Grant Number 82073328).

Personalized auto-segmentation for magnetic resonance imaging-guided adaptive radiotherapy of large brain metastases

BACKGROUND AND PURPOSE

Magnetic resonance-guided adaptive radiotherapy (MRgART) may improve the efficacy of large brain metastases (BMs)(≥2 cm), whereas the workflow requires optimized. This study develops a two-stage, personalized deep learning auto-segmentation (DLAS) model to assist online delineation of large BMs.

MATERIALS AND METHODS

Multi-sequences images from 177 BMs were trained to develop the basic DLAS model. Then, 741 daily online MR images of 20 large BMs from a prospective trial were collected for developing a personalized model. The dice similarity coefficient (DSC) was evaluated across three methods: basic model, rigid registration and personalized model, at intervals of every five fractions. The accuracy and efficiency were compared between manual delineation (MD) and DLAS assistant delineation (DLAS-AD) in 8 patients who underwent contrast T1 re-scan during MRgART.

RESULTS

The personalized DLAS model demonstrated significantly better performance compared to the basic model and rigid registration during the last fraction of MRgART (when the tumor volume achieved a significant reduction). The mean DSC for basic model vs. rigid registration vs. personalized model were 0.86 (p = 0.01) vs. 0.88 (p = 0.05) vs. 0.90, respectively. The DLAS-AD significantly improved contouring accuracy compared to MD, with a mean DSC of 0.89 vs. 0.85 (p = 0.001), and reduced contouring time by an average of 53.5 % (193 s vs. 424 s, p < 0.001).

CONCLUSION

Personalized DLAS model may increase the accuracy and efficiency of MD to optimize the workflow of MRgART for large BMs.

Assessing the Relationship Between MR-Based Functional Dose Metrics and Post-Stereotactic Body Radiation Therapy Albumin-Bilirubin Change

PURPOSE

This study aimed to identify predictors of global liver function change measured by albumin-bilirubin (ALBI) score following stereotactic body radiation therapy (SBRT) in patients with hepatocellular carcinoma (HCC). By integrating gadoxetic acid-enhanced magnetic resonance imaging (MRI) uptake and dosimetric data, the goal was to develop functional-based treatment-planning strategies that preserve hepatic function.

METHODS AND MATERIALS

Twenty-five patients with HCC enrolled on an institutional review board-approved adaptive SBRT trial had liver dynamic gadoxetic acid-enhanced MRI and blood sample collections before and 1 month after SBRT. Gadoxetic acid uptake rate (k1) maps were quantified for regional hepatic function and coregistered to both 2-Gy equivalent dose and physical dose distributions. Mean or integral-based metrics, dose-volume or function-volume histogram metrics, and function-dose-volume histogram metrics were calculated. These metrics were correlated with percentage ALBI score changes by Spearman rank correlation with Bonferroni correction.

RESULTS

We found that the greater the sparing of liver with high-hepatic function (k1 intensity), the less the decline of ALBI score post-RT. The threshold for preserving global hepatic function was 10 % of the maximum k1 intensity and 5 Gy EQD2. The integration of regional function (k1) and dosimetric data improved the ability to predict ALBI score changes compared with dosimetric or functional data alone.

CONCLUSIONS

Combining regional liver function metrics from gadoxetic acid-enhanced MRI with radiation dose provides a robust model for predicting ALBI score changes following SBRT. These findings suggest that there is a potential for functional-based treatment planning to better preserve liver function in patients with HCC undergoing SBRT. Future studies are needed to externally validate these findings.

Pediatric CNS Radiation Oncology: Recent Developments and Novel Techniques

Radiation therapy (RT) is a cornerstone in the management of pediatric central nervous system (CNS) tumors. Recent advancements in RT delivery and techniques aim to enhance therapeutic effectiveness while minimizing both acute and long-term complications associated with pediatric brain RT. This paper highlights innovative developments in the field, including the clinical indications, benefits, and challenges of proton therapy and stereotactic radiotherapy. The ongoing refinement of risk-adapted RT volumes is highlighted, with examples of newly proposed germinoma RT volumes and hippocampal-sparing RT. Additionally, emerging experimental approaches, including FLASH therapy and theranostics, are also discussed as promising future directions. Further prospective, multi-institutional collaborative studies are essential to validate and expand upon the benefits outlined in this review.

Dosimetric and radiobiological evaluation of stereotactic radiosurgery using volumetric modulated arc therapy and dynamic conformal arc therapy for multiple brain metastases

This paper presents a clinical comparison of the target dose, normal tissue complication probability (NTCP), and plan quality between volumetric modulated conformal arc therapy (VMAT) against dynamic conformal arc therapy (DCAT) techniques to facilitate clinical decision-making in multiple brain metastases (MBM) treatment. A total of 11 cases having 33 lesions were recruited at the Union Oncology Centre, Union Hospital, Hong Kong SAR. With CT images available, all plans were optimized using both HyperArc (HA) and Brainlab Elements Multiple Brain Metastases (Elements MBM). Target coverage, normal tissue sparing, and dose distribution were compared pairwise between VMAT and DCAT. Results showed that the plans generated using both techniques achieved adequate target coverage to meet up with the oncologist's prescription. With similar levels of NTCP, the normal brain received low doses of radiation using both techniques and the risk of brain necrosis was kept equally low. This indicated that VMAT and DCAT produced similar high-quality treatment plans with low risks of brain necrosis. Meanwhile, VMAT showed better homogeneity which could potentially be more useful for large targets, while DCAT showed better target conformity especially for targets smaller than 1 cc. In general, both HA and Elements MBM demonstrated ability to generate high-quality clinical plans.

MRI distortion correction is associated with improved local control in stereotactic radiotherapy for brain metastases

Distortions in brain MRI caused by gradient nonlinearities may reach several millimeters, thus distortion correction is strongly recommended for radiotherapy treatment planning. However, the significance of MRI distortion correction on actual clinical outcomes has not been described yet. Therefore, we investigated the impact of planning MRI distortion correction on subsequent local control in a historic series of 419 brain metastases in 189 patients treated with stereotactic radiotherapy between 01/2003 and 04/2015. Local control was evaluated using a volumetric extension of the RANO-BM criteria. The predictive significance of distortion correction was assessed using competing risk analysis. In this cohort, 2D distortion-corrected MRIs had been used for treatment planning in 52.5% (220/419) of lesions, while uncorrected MRIs had been employed in 47.5% (199/419) of metastases. 2D distortion correction was associated with improved local control (Cumulative incidence of local progression at 12 months: 14.3% vs. 21.2% and at 24 months: 18.7% vs. 28.6%, p = 0.038). In multivariate analysis, adjusting for histology, baseline tumor volume, interval between MRI and treatment delivery, year of planning MRI, biologically effective dose and adjuvant Whole-brain radiotherapy, use of distortion correction remained significantly associated with improved local control (HR 0.55, p = 0.020). This is the first study to clinically evaluate the impact of MRI gradient nonlinearity distortion correction on local control in stereotactic radiotherapy for brain metastases. In this historic series, we found significantly higher local control when using 2D corrected vs. uncorrected MRI studies for treatment planning. These results stress the importance of assuring that MR images used for radiotherapy treatment planning are properly distortion-corrected.

Phase 1/2 Dose Escalation Trial of 3-Fraction Stereotactic Radiosurgery for Resection Cavities from Large Brain Metastases

PURPOSE

We performed a dose escalation trial of hypofractionated stereotactic radiosurgery (SRS) to determine the maximum tolerated dose (MTD) of 3-fraction SRS for brain metastases resection cavities.

METHODS AND MATERIALS

Following surgical resection of a brain metastasis, patients were enrolled by SRS treatment volume onto 2 arms: arm 1 = 4.2-14.1 cm3, approximating a 2 to 3 cm diameter sphere, and arm 2 = 14.2-33.5 cm3 or a 3 to 4 cm sphere equivalent. Dose escalation levels were 24, 27, 30, and 33 Gy in 3 consecutive-day fractions, with 6 patients at each dose level in a 6 + 6 trial design. Dose-limiting toxicity was defined as either acute (within 30 days of SRS) grade 3 to 5 central nervous system toxicity and/or late grade 3 to 5 radiation necrosis occurring at any subsequent timepoint. The MTD was defined as the highest dose where 0 to 1 out of 6 or 0 to 3 out of 12 had a dose-limiting toxicity.

RESULTS

From 2009 to 2014, 48 evaluable patients were enrolled. One (2%) patient had acute G3 toxicity; dose escalation proceeded to 33 Gy. No MTD was reached. Overall, 14 (29%) of 48 patients had G1-4 late radiation necrosis; G1 in 4 (8%), G2 in 6 (13%), G3 in 2 (4%), and G4 in 2 (4%). At the 33 Gy dose level, any grade necrosis was 58% in all 12 patients, 83% in the 6 patients on the larger volume arm 2; no G3-4 necrosis occurred in smaller arm 1 targets. With a median overall survival of 24 months (95% CI, 18-35), the 1-year cumulative incidence rates were: 10% (95% CI, 3.8-21) for local progression, 48% (95% CI, 33-61) for distant intracranial progression, and 13% (95% CI, 5-24) for radiation necrosis. Nodular meningeal disease occurred in 15% (7 of 48) of patients.

CONCLUSIONS

Grade 3 to 4 toxicity was 8% and no MTD was reached with dose escalation to 33 Gy in 3 fractions. However, with a 58% incidence of G1-4 radiation necrosis at the 33 Gy level and 33% G3-4 necrosis at 30 Gy on arm 2, a 3-fraction dose of 27-30 Gy for targets 2 to 3 cm and 27 Gy for targets 3 to 4 cm may provide the optimal balance between toxicity and tumor control. A dose of 33 Gy is reserved for cavities <3 cm where tumor control may benefit from higher doses.

Spatial accuracy of dose delivery significantly impacts the planning target volume margin in linear accelerator-based intracranial stereotactic radiosurgery

The impact of three-dimensional (3D) dose delivery accuracy of C-arm linacs on the planning target volume (PTV) margin was evaluated for non-coplanar intracranial stereotactic radiosurgery (SRS). A multi-institutional 3D starshot test using beams from seven directions was conducted at 22 clinics using Varian and Elekta linacs with X-ray CT-based polymer gel dosimeters. Variability in dose delivery accuracy was observed, with the distance between the imaging isocenter and each beam exceeding 1 mm at one institution for Varian and nine institutions for Elekta. The calculated PTV margins for Varian and Elekta linacs that could cover the gross tumor volume with 95% probability at 95% of the institutions were 2.3 and 3.5 mm, respectively, in the superior-inferior direction. However, with multifactorial system management (i.e., high-accuracy 3D dose delivery with rigorous linac quality assurance, strict patient immobilization, and high intra-fractional positioning accuracy), these margins could be reduced to 1.0 mm and 1.5 mm, respectively. The findings indicate significant millimeter-level variability in 3D dose delivery accuracy among linacs installed in clinical settings. Thus, maximizing a linac's 3D dose delivery accuracy is essential to achieve the required PTV margin in intracranial SRS.

Metastasis-directed stereotactic radiotherapy in patients with breast cancer: results of an international multicenter cohort study

Metastasis-directed therapy (MDT) for oligometastatic breast cancer (≤ 5 metastases) has shown little effect in specific scenarios of randomized trials. Therefore, we aimed to assess outcomes after metastasis-directed stereotactic radiotherapy (SRT) in various clinical scenarios. We conducted an international retrospective cohort study in thirteen centers including breast cancer patients receiving SRT to any metastatic site. Outcomes included local recurrence (LR), progression-free survival (PFS), and overall survival (OS). Cumulative incidence analysis was used for LR, Kaplan-Meier estimates for PFS and OS. Covariables included patient, disease, and SRT characteristics. We performed univariable and multivariable analyses (MVA). Among 444 patients, 751 metastases were treated with SRT. Of these, 73% were intracranial and 27% extracranial lesions. Oligometastatic disease (OMD) was present in 66% of the patients. LR after two years occurred significantly more often in intracranial (25%) versus extracranial lesions (7%). In MVA of patients with OMD treated for intracranial sites, higher performance status was significantly associated with longer PFS. Further, higher performance status, biologic subtype (HR-pos./HER2-pos.), and MDT to all sites were significantly associated with longer OS. In MVA of oligometastatic patients treated for extracranial sites, biologic subtype (HR-neg./HER2-pos.) and synchronous metastasis were associated with significantly longer PFS, whereas higher grading was associated with significantly shorter PFS. Moreover, biologic subtype (HR-neg./HER2-neg.) was associated with significantly shorter OS. In conclusion, the role of MDT for breast cancer may vary per clinical scenario. Patients with OMD treated for intracranial lesions who had MDT to all sites showed superior OS. Our results should be validated prospectively.

Impacts of Calculation Grid Spacing and Statistical Uncertainty of Monte Carlo Algorithm on Stereotactic Radiosurgery Planning With Volumetric-Modulated Arcs for Single Brain Metastases Using the Monaco® System

Purpose In linac-based stereotactic radiosurgery (SRS) utilizing a multileaf collimator (MLC) for brain metastases (BMs), a volumetric-modulated arc (VMA) technique is indispensable for generating a suitable dose distribution with efficient planning and delivery. However, the optimal calculation grid spacing (GS) and statistical uncertainty (SU) of the Monte Carlo algorithm for VMA optimization have yet to be determined. This planning study aimed to examine the impacts of GS and GU settings on VMA-based SRS planning and to find the optimal combination for templating. Materials and methods Thirty clinical BMs with a gross tumor volume (GTV) of 0.08-48.09 cc (median 9.81 cc) were included. The treatment platform included a 5-mm leaf-width MLC Agility® (Elekta AB, Stockholm, Sweden) and a planning system Monaco® (Elekta AB). The prescribed dose was uniformly assigned to the GTV D V-0.01 cc, the minimum dose of GTV minus 0.01 cc, i.e., D >95% for GTV >0.20 cc or to the GTV D 95% for GTV ≤0.20 cc, to minimize the uncovered GTV to the equivalent of a 3 mm diameter lesion. Five combinations of GS and SU per plan were examined for 12 selected GTVs (median 17.41 cc): GS of 2 mm and SU of 3% (G2U3), 2 mm and 2% (G2U2), 2 mm and 1% (G2U1), 1 mm and 2% (G1U2), and 1 mm and 1% (G1U1). Otherwise, the same arc arrangement and optimization method were uniformly used to prioritize the GTV dose conformity and the steepness of the dose gradient outside the GTV without dose constraints inside the GTV boundary. Further comparisons were conducted using 30 GTVs between the two groups with the highest plan quality. Results The G2U3 and G2U2 resulted in the equivalent total calculation time (tCT) and exactly the same plan quality. The overall plan quality was significantly superior in the G1U2 and G1U1 than in the G2U1 and G2U2, although the tCT was significantly longer in the G1U1 and G1U2 than in the G2U1 and G2U2. In the comparison of the G1U2 and G1U1, the concentric lamellarity of dose gradients 2 mm outside and 2-4 mm inside the GTV boundary was significantly superior in the G1U1 than in the G1U2, while there was no significant difference in the other parameters. The tCT tended to be longer in the G1U1 than in the G1U2. Conclusions The initial settings of GS and SU have significant impacts on the plan quality and tCT. The settings with GS of 1 mm and SU of 1% per plan are recommended to create the most suitable dose distribution for single BMs, especially for irregularly shaped and/or large lesions, although the tCT is long. In addition to common evaluation metrics, the coverage values of 2 mm outside and 2-4 mm inside the GTV surface by the D eIIV, the minimum dose to cover the irradiated isodose volume equivalent to each target volume, are valuable for in-depth plan comparison.

Analysis of linear accelerator-based fractionated stereotactic radiotherapy in brain metastases: efficacy, safety, and dose tolerances

Objective

To assess the efficacy and safety of linear accelerator-based fractionated stereotactic radiotherapy (LINAC-FSRT) in patients with brain metastases (BM).

Methods

We retrospectively analyzed 214 patients treated with LINAC-FSRT, categorized based on biologically effective dose (BED10, α/β = 10) into two groups (≤55 Gy, >55 Gy). Stratified analyses were conducted based on targeted therapy to compare survival outcomes. To examine brain tissue dose-tolerance volume, patients were divided into two groups: the standard Hypofractionated Treatment Effects in the Clinic (HyTEC) protocol group and an adjusted HyTEC protocol group where dose-volume restrictions exclude the planning target volume (PTV).

Results

Results as of December 2023 showed median intracranial progression-free survival (iPFS) at 12.4 months, with median overall survival (OS) not reached and a one-year local control (LC) rate of 68.7%. Mild to moderate toxicity affected 17.3% of patients, while severe toxicity occurred in 2.8%. Multivariate Cox analysis indicated that uncontrolled extracranial disease significantly reduced iPFS (HR = 2.692, 95%CI:1.880-3.853, P < 0.001) and OS (HR = 3.063, 95%CI:1.987-4.722, P < 0.001). BED10 >55 Gy (HR = 0.656, 95%CI:0.431-0.998, P = 0.049) improved OS, showing statistical significance (P = 0.037) without affecting iPFS or CNS toxicity (P = 0.127, P = 0.091). Stratified analysis highlighted nearly significant OS improvements with high-dose FSRT and targeted therapy (P = 0.054), while concurrent therapy markedly enhanced iPFS (P = 0.027). No significant differences were observed in intracranial local failure (ILF-which represents progression in previously treated areas during follow-up), one-year LC rates, iPFS, or OS between dose-volume groups. Adjusting HyTEC volume restrictions did not significantly increase CNS adverse reactions (P = 0.889).

Conclusions

LINAC-FSRT is safe and effective in BM. BED10>55 Gy notably enhances OS post-LINAC-FSRT and may benefit LC. High BED10 FSRT with targeted therapy likely boosts synergy, and concurrent targeted therapy significantly improves iPFS. Diminishing dose volume constraints at different fractions based on the HyTEC guidelines is feasible.

Delayed and Concurrent Stereotactic Radiosurgery in Immunotherapy-Naïve Melanoma Brain Metastases

Melanoma remains a formidable challenge in oncology, causing the majority of skin cancer deaths in the United States, with brain metastases contributing substantially to this mortality. This paper reviews the current therapeutic strategies for melanoma brain metastases, with a focus on delayed and concurrent stereotactic radiosurgery (SRS). While surgery and traditional chemotherapy offer limited efficacy, recent advances in immunotherapy, particularly immune checkpoint inhibitors (ICIs), have played a major role in the advancement and improved efficacy of the treatment of cancers, including brain metastases. Recent studies indicate that monotherapy with ICIs may lead to a higher median overall survival compared to historical benchmarks, potentially allowing patients to delay radiosurgery. Other studies have found that combining SRS with ICIs demonstrates promise, with results indicating improved intracranial control. Ongoing clinical trials explore novel combinations of immunotherapies and radiotherapies, aiming to optimize treatment outcomes while minimizing adverse effects. As treatment options expand, future studies will be necessary to understand the interplay between therapies and their optimal sequencing to improve patient outcomes.

ACROPath Oligometastases: The American College of Radiation Oncology Clinical Pathway

Radiation oncology is among the most data-driven specialties in medicine. Recently, a wealth of peer-reviewed data has been published supporting the treatment of oligometastatic malignancies, demonstrating improved survival with metastasis-directed therapy, such as stereotactic body radiation therapy (SBRT), when combined with appropriate patient selection and treatment. However, there are currently few, if any, established guidelines that synthesize the abundance of data specific to radiotherapy into a single, easily accessed resource for clinicians. ACROPath® is a major initiative of the American College of Radiation Oncology (ACRO) that aims to present aggregated clinical pathway data in a highly usable format that is readily accessible to clinicians at the point of care in real time. The oligometastases pathway is the first published algorithm in this collection, with additional pathways anticipated in future publications. Clinical radiation oncologists with expertise in the treatment and management of oligometastatic disease were recruited from across ACRO's diverse membership, including both academic and private practice physicians, to ensure a broad-based experience and insight. Individual participants were assigned subsections of the pathway for guideline development, and then, each subsection was presented to the full group for evaluation and consensus development based on published data. Rather than presenting an unstructured set of treatment options, as is common in other treatment guidelines, this initiative aimed to categorize appropriate treatments based on published clinical evidence in a hierarchy further ranked by efficacy, toxicity, and cost. Based on these strata, treatment recommendations were collated and grouped into three rank categories (gold, silver, or bronze) to denote the degree of applicability. The team assembled an interactive document that will eventually be available online, and it is summarized in detail here. Recommendations are grouped both by the anatomic site of metastasis and by the primary tumor type, recognizing that original histology might impact the treatment differently in different anatomic locations. After a review of available published clinical evidence, the committee reached a consensus on all recommendations presented, categorizing each option as gold, silver, or bronze to guide clinicians appropriately. This first iteration of ACROPath® Oligometastases represents one of the few comprehensive clinical decision support tools available for managing patients with limited metastatic disease. It presents available data in a highly accessible, easily used reference, which will be formally reviewed and updated by the committee as frequently as emerging data requires, likely at six- to 12-month intervals.

Initial Experience of Implementing a Pre-treatment Dry Run for HyperArc Stereotactic Radiosurgery Treatments With Optical Surface Imaging for Intra-fraction Motion Monitoring

Linac-based stereotactic radiosurgery (SRS) with planning target volume (PTV) margins <1 mm has become increasingly common in recent years. Optical surface imaging for surface-guided radiation therapy (SGRT) is often used for intra-fraction motion monitoring during these treatments to facilitate the use of a smaller PTV margin by providing real-time quantitative patient positioning information. However, rotating the couch introduces errors to SGRT-reported translations and rotations that can be problematic for SRS treatments with non-coplanar arcs and very small PTV margins. This work presents a novel approach for decreasing the magnitude of these errors by performing a pre-treatment dry run and capturing reference surfaces with the SGRT system at each couch angle included in the treatment plan. Time from cone beam computed tomography (CBCT) to treatment initiation and total treatment session time were reviewed for 30 single-fraction brain SRS cases treated using this technique to determine the effect of including the dry run on treatment session times. Out of the 30 cases treated between April 2023 and January 2024, 23 treatments required only a single CBCT prior to treatment, with no additional mid-treatment imaging required to verify patient positioning after motion. The median time between CBCT and treatment initiation was 7.98 minutes (interquartile range (IQR) = 7.28 to 8.93 minutes). The median time from CBCT to treatment completion was 15.43 minutes (IQR = 13.67 to 21.97 minutes). In the six patients that required one additional CBCT, the treatment session times ranged from 24.32 to 32.83 minutes. There was one patient who required three mid-treatment CBCTs, and the treatment session time was 67.87 minutes. Incorporating the pre-treatment dry run with the acquisition of reference surfaces at each treatment angle decreased errors in SGRT-reported translations and rotations associated with couch rotation without significantly increasing treatment session times.

Dose escalation with stereotactic body radiotherapy for cervical cancer treatment

BACKGROUND

Dose escalation with brachytherapy after pelvic irradiation is standard for treating cervical cancer. Its application can be impossible for some patients. Dose escalation with SBRT is widely used with high local control and acceptable toxicity rates in different body parts. The study enrolled patients who underwent SBRT treatment for dose escalation in the cervix.

METHODS

Patients who were pathologically diagnosed and treated with cervical SBRT after definitive CRT were included in the study. A total of 30 Gy in 5 fractions for the high-risk volume was prescribed. The first response evaluation was performed three months after the completion of treatment. Treatment toxicity was documented according to the RTOG-EORTC scale. Oncological outcomes and toxicity were assessed.

RESULTS

Between 02.2019 and 05.2023, 40 patients were treated with an SBRT boost after pelvic irradiation. The median follow-up time was 16 months (7-44 months). The median HR CTV was 47 cc (8,3-168,2 cc). There were 39 patients who achieved a complete response and one who achieved a partial response in the third month after treatment. There were two local or two regional recurrences. The 1-year metastasis-free survival was 88%, and the 1-year progression-free survival was 88%. During the follow-up period, one grade 3 gastrointestinal side effect was observed.

CONCLUSIONS

SBRT which has low toxicity and reasonable locoregional control rates in a short follow-up period, may be an option for dose escalation in brachytherapy-ineligible cervical cancer patients.

Fractionated Stereotactic Intensity-Modulated Radiotherapy for Large Brain Metastases: Comprehensive Analyses of Dose-Volume Predictors of Radiation-Induced Brain Necrosis

BACKGROUND

The objective was to explore dosimetric predictors of brain necrosis (BN) in fractionated stereotactic radiotherapy (SRT).

METHODS

After excluding collinearities carefully, multivariate logistic models were developed for comprehensive analyses of dosimetric predictors in patients who received first-line fractionated SRT for brain metastases (BMs). The normal brain volume receiving an xx Gy biological dose in 2 Gy fractions (VxxEQD2) was calculated from the retrieved dose-volume parameters.

RESULTS

Thirty Gy/3 fractions (fr) SRT was delivered to 34 patients with 75 BMs (median target volume, 3.2 cc), 35 Gy/5 fr to 30 patients with 57 BMs (6.4 cc), 37.5 Gy/5 fr to 28 patients with 47 BMs (20.2 cc), and 40 Gy/10 fr to 20 patients with 37 BMs (24.3 cc), according to protocols, depending on the total target volume (p < 0.001). After excluding the three-fraction groups, the incidence of symptomatic BN was significantly higher in patients with a larger V50EQD2 (adjusted odds ratio: 1.07, p < 0.02), V55EQD2 (1.08, p < 0.01), or V60EQD2 (1.09, p < 0.01) in the remaining five- and ten-fraction groups. The incidence of BN was also significantly higher in cases with V55EQD2 > 30 cc or V60EQD2 > 20 cc (p < 0.05). These doses correspond to 28 or 30 Gy/5 fr and 37 or 40 Gy/10 fr, respectively.

CONCLUSIONS

In five- or ten-fraction SRT, larger V55EQD2 or V60EQD2 are BN risk predictors. These biologically high doses may affect BN incidence. Thus, the planning target volume margin should be minimized as much as possible.

Dosimetric and Clinical Prognostic Factors in Single-Isocenter Linac-Based Stereotactic Radiotherapy for Brain Metastases

Background/Objectives: To report on predictive factors in Linac-based SRT for single and multiple BM. Methods: Consecutive patients receiving either one or three fractions of single-isocenter coplanar VMAT SRT were retrospectively included. The GTV-PTV margin was 1-2 mm. The delivered target dose was estimated by recalculating the original plans on roto-translated CT according to errors recorded by post-treatment CBCT. The Kaplan-Meier method estimated local progression-free survival (LPFS), intracranial progression-free survival (IPFS), and overall survival (OS). Log-rank and Wilcoxon-Mann-Whitney tests evaluated inter-group differences, whereas Cox regression analysis assessed prognostic factors. Results: Fifty females and fifty males, with a median age of 69 years, received 107 SRTs. A total of 213 BM (range, 1-10 per treatment) with a median volume of 0.22 cc were irradiated with a median minimum BED of 59.5 Gy. The median delivered GTV D95 reduction was -0.3%. The median follow-up was 11 months. Nineteen LP events and a 1-year LC rate of 90.1% were observed. The GTV coverage did not correlate with LC, while the GTV volume was a risk factor for LP, with the 1-year rate dropping to 73% for volumes ≥ 0.88 cc. The median LPFS, IPFS, and OS were 6, 5, and 7 months, respectively. Multivariate analysis showed that patients with melanoma histology and those receiving a second or subsequent systemic therapy line had the worst outcomes, whereas patients with adenocarcinoma histology and mutations showed better results. Conclusions: The accuracy and efficacy of the Linac-based SRT approach for BM were confirmed, but the dose distribution alone failed to predict the treatment response, suggesting that other factors must be considered to maximize SRT outcomes.

Two-Day Fraction Gamma Knife Radiosurgery for Large Brain Metastasis

OBJECTIVE

We investigated how treating large brain metastasis (LBM) using 2-day fraction Gamma Knife radiosurgery (GKRS) affects tumor control and patient survival. A prescription dose of 10.3 Gy was applied for 2 consecutive days, with a biologically effective dose equivalent to a tumor single-fraction dose of 16.05 Gy and a brain single-fraction dose of 15.12 Gy.

METHODS

Between November 2017 and December 2021, 42 patients (mean age, 68.3 years; range, 50-84 years; male, 29 [69.1%]; female, 13 [30.9%]) with 44 tumors underwent 2-day fraction GKRS to treat large volume brain metastasis. The main cancer types were non-small cell lung cancer (n=16), small cell lung cancer (n=7), colorectal cancer (n=7), breast cancer (n=3), gastric cancer (n=2), and other cancers (n=7). Twenty-one patients (50.0%) had a single LBM, 19 (46.3%) had a single LBM and other metastases, and two had two (4.7%) large brain metastases. At the time of the 2-day fraction GKRS, the tumors had a mean volume of 23.1 mL (range, 12.5-67.4). On each day, radiation was administered at a dose of 10.3 Gy, mainly using a 50% isodose-line.

RESULTS

We obtained clinical and magnetic resonance imaging follow-up data for 34 patients (81%) with 35 tumors, who had undergone 2-day fraction GKRS. These patients did not experience acute or late radiation-induced complications during follow-up. The median and mean progression-free survival (PFS) periods were 188 and 194 days, respectively. The local control rates at 6, 9, and 12 months were 77%, 40%, and 34%, respectively. The prognostic factors related to PFS were prior radiotherapy (p=0.019) and lung cancer origin (p=0.041). Other factors such as tumor volumes, each isodose volumes, and peri-GKRS systemic treatment were not significantly related to PFS. The overall survival period of the 44 patients following repeat stereotactic radiosurgery (SRS) ranged from 15-878 days (median, 263±38 days; mean, 174±43 days) after the 2-day fraction GKRS. Eight patients (18.2%) were still alive.

CONCLUSION

Considering the unsatisfactory tumor control, a higher prescription dose should be needed in this procedure as a salvage management. Moreover, in the treatment for LBM with fractionated SRS, using different isodoses and prescription doses at the treatment planning for LBMs should be important. However, this report might be a basic reference with the same fraction number and prescription dose in the treatment for LBMs with frame-based SRS.

A high-density multi-electrode platform examining the effects of radiation on in vitro cortical networks

Radiation therapy and stereotactic radiosurgery are common treatments for brain malignancies. However, the impact of radiation on underlying neuronal circuits is poorly understood. In the prefrontal cortex (PFC), neurons communicate via action potentials that control cognitive processes, thus it is important to understand the impact of radiation on these circuits. Here we present a novel protocol to investigate the effect of radiation on the activity and survival of PFC networks in vitro. Escalating doses of radiation were applied to PFC slices using a robotic radiosurgery platform at a standard dose rate of 10 Gy/min. High-density multielectrode array recordings of radiated slices were collected to capture extracellular activity across 4,096 channels. Radiated slices showed an increase in firing rate, functional connectivity, and complexity. Graph-theoretic measures of functional connectivity were altered following radiation. These results were compared to pharmacologically induced epileptic slices where neural complexity was markedly elevated, and functional connections were strong but remained spatially focused. Finally, propidium iodide staining revealed a dose-dependent effect of radiation on apoptosis. These findings provide a novel assay to investigate the impacts of clinically relevant doses of radiation on brain circuits and highlight the acute effects of escalating radiation doses on PFC neurons.

Non-coplanar Arc-Involved Beam Arrangement With Sufficient Arc Rotations Is Suitable for Volumetric-Modulated Arc-Based Radiosurgery for Single Brain Metastasis

Introduction In linac-based stereotactic radiosurgery (SRS) leveraging a multileaf collimator (MLC) for brain metastasis (BM), volumetric-modulated arcs (VMAs) enable the generation of a suitable dose distribution with efficient planning and delivery. However, the arc arrangement, including the number of arcs, allocation, and rotation ranges, varies substantially among devices and facilities. Some modalities allow coplanar arc(s) (CA(s)) or beam(s) alone, and some facilities only use them intentionally despite the availability of non-coplanar arcs (NCAs). The study was conducted to examine the significance of NCAs and the optimal arc rotation ranges in VMA-based SRS for a single BM. Materials and methods This was a planning study for the clinical scenario of a single BM, including 20 clinical cases with a gross tumor volume (GTV) of 0.72-44.30 cc. Three different arc arrangements were compared: 1) reciprocating double CA alone of each 360º rotation with different collimator angles of 0 and 90º, 2) one CA and two NCAs of each 120º rotation with the shortest beam path lengths to the irradiation isocenter (NCA_L), and 3) one CA of 360º rotation and two NCAs of each 180º rotation (NCA_F). The three arcs were allocated similarly to equally divide the cranial hemisphere with different collimator angles of 0, 45, and 90º. Three VMA-based SRS plans were generated for each GTV using a 5 mm leaf-width MLC with the identical optimization method that prioritized the steepness of dose gradient outside the GTV boundary without any constraints to the GTV internal dose. A prescribed dose was uniformly assigned to the GTV D V-0.01 cc, the minimum dose of GTV minus 0.01 cc. The GTV dose conformity, the steepness of dose gradients both outside and inside the GTV boundary, the degree of concentric lamellarity of the dose gradients, and the appropriateness of the dose attenuation margin outside the GTV boundary were evaluated using metrics appropriate for each. Results The arc arrangements including NCAs showed significantly steeper dose gradients both outside and inside the GTV boundary with smaller dose attenuation margins than the CAs alone, while NCAs showed no significant advantage on the GTV dose conformity. In the NCA-involved arc arrangements, the NCA_F was significantly superior to the NCA_L in terms of the GTV dose conformity, the steepness of dose gradient outside the GTV, the degree of concentric lamellarity of the dose gradients outside and inside the GTV boundary, and the appropriateness of dose attenuation margin. However, the NCA_F showed no significant advantage on the steepness of dose increase inside the GTV boundary over the NCA_L. The dose increase just inside the prescribed isodose surface to the GTV boundary was significantly steeper with the NCA_L than the NCA_F. Conclusions In VMA-based SRS for a single BM, an arc arrangement including NCAs is indispensable, and sufficient arc rotations are suitable for achieving a dose distribution that maximizes therapeutic efficacy and safety in comparison to limited ones which are appropriate for dynamic conformal arcs. Although VMA with CAs alone can provide a non-inferior GTV dose conformity to NCAs, CA(s) alone should be applied only to situations where shorter irradiation time is prioritized over efficacy and safety.

Comprehensive analysis of stereotactic Radiosurgery outcomes in triple-negative breast cancer patients with brain metastases: The influence of immunotherapy and prognostic factors

INTRODUCTION

Breast cancer stands as the second most common solid tumors with a propensity for brain metastasis. Among metastatic breast cancer cases, the brain metastasis incidence ranges from 10 % to 30 %, with triple-negative breast cancer (TNBC) displaying a heightened risk and poorer prognosis. SRS has emerged as an effective local treatment modality for brain metastases; however, data on its outcomes specifically in pure triple-negative subtype remain scarce.

METHOD

We retrospectively reviewed the electronic medical records of all brain metastasis (BM) TNBC patients treated with SRS. Patient, tumour characteristics and treatment details data were collected. This retrospective cohort study aimed to evaluate local control (LC), distant brain metastasis free survival (DBMFS), and overall survival (OS) outcomes in TNBC patients undergoing SRS for brain metastases while identifying potential prognostic factors.

RESULT

Forty-three patients with TNBC and brain metastases treated with SRS between January 2017 and 2023 were included. The study found rates of LC (99 % at 1 year) and DBMFS (76 % at 1 year) after SRS, with brain metastasis count (p = 0,003) and systemic treatment modality (p = 0,001) being significant predictors of DBMFS. The median OS following SRS was 19.5 months, with neurological deficit (p = 0.003) and systemic treatment modality (p = 0.019) identified as significant predictors of OS.

CONCLUSION

SRS demonstrates favourable outcomes in terms of local control and distant brain metastasis-free survival in TNBC. Neurological deficit and systemic treatment significantly influence overall survival, emphasizing the importance of personalized treatment approaches and (magnetic resonance imaging) MRI surveillance based on these factors.

Hypofractionated stereotactic radiotherapy for brain metastases in lung cancer patients: dose‒response effect and toxicity

BACKGROUND

Lung cancer is a common cause of brain metastases, approximately 40% of patients with lung cancer will develop brain metastases at some point during their disease. Hypofractionated stereotactic radiotherapy (HSRT) has been demonstrated to be effective in controlling limited brain metastases. However, there is still no conclusive on the optimal segmentation of HSRT. The aim of our study was to explore the correlation between the HSRT dosage and its treatment effect and toxicity.

METHODS

A retrospective analysis was conducted on patients with non-small cell lung cancer (NSCLC) brain metastasis at Hangzhou Cancer Hospital from 1 January 2019 to 1 January 2021. The number of brain metastases did not exceed 10 in all patients and the number of fractions of HSRT was 5. The prescription dose ranges from 25 to 40 Gy. The Kaplan-Meier method was used for estimation of the localised intracranial control rate (iLC). Adverse radiation effects (AREs) were evaluated according to CTCAE 5.0. This study was approved by the Institutional Ethics Review Board of the Hangzhou Cancer Hospital (#73/HZCH-2022).

RESULTS

Forty eligible patients with a total of 70 brain metastases were included in this study. The 1-year iLC was 76% and 89% in the prescribed dose ≤ 30 Gy and > 30 Gy group, respectively (P < 0.05). For patients treated with HSRT combined with targeted therapy, immunotherapy and chemotherapy, the 1-year iLC was 89%, 100%, and 45%, respectively. No significant associations were observed between the number, maximum diameter, location, and type of pathology of brain metastases. The rate of all-grade AREs was 33%. Two patients who received a total dose of 40 Gy developed grade 3 headache, the rest of the AREs were grade 1-2.

CONCLUSIONS

Increasing the prescription dose of HSRT improves treatment effect but may also exacerbate the side effects. Systemic therapy might impact the iLC rate, and individualized treatment regimens need to be developed.

Association of increasing gross tumor volume dose with tumor volume reduction and local control in fractionated stereotactic radiosurgery for unresected brain metastases

BACKGROUND

Fractionated stereotactic radiosurgery (fSRS) is an important treatment strategy for unresected brain metastases. We previously reported that a good volumetric response 6 months after fSRS can be the first step for local control. Few studies have reported the association between gross tumor volume (GTV) dose, volumetric response, and local control in patients treated with the same number of fractions. Therefore, in this study, we aimed to investigate the GTV dose and volumetric response 6 months after fSRS in five daily fractions and identify the predictive GTV dose for local failure (LF) for unresected brain metastasis.

METHODS

This retrospective study included 115 patients with 241 unresected brain metastases treated using fSRS in five daily fractions at our hospital between January 2013 and April 2022. The median prescription dose was 35 Gy (range, 30-35 Gy) in five fractions. The median follow-up time after fSRS was 16 months (range, 7-66 months).

RESULTS

GTV D80 > 42 Gy and GTV D98 > 39 Gy were prognostic factors for over 65% volume reduction (odds ratio, 3.68, p < 0.01; odds ratio, 4.68, p < 0.01, respectively). GTV D80 > 42 Gy was also a prognostic factor for LF (hazard ratio, 0.37; p = 0.01).

CONCLUSIONS

GTV D80 > 42 Gy in five fractions led to better volume reduction and local control. The goal of planning an inhomogeneous dose distribution for fSRS in brain metastases may be to increase the GTV D80 and GTV D98. Further studies on inhomogeneous dose distributions are required.

MRI radiomics predicts the efficacy of EGFR-TKI in EGFR-mutant non-small-cell lung cancer with brain metastasis

AIM

To develop and validate models based on magnetic resonance imaging (MRI) radiomics for predicting the efficacy of epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) in EGFR-mutant non-small-cell lung cancer (NSCLC) patients with brain metastases.

MATERIALS AND METHODS

117 EGFR-mutant NSCLC patients with brain metastases who received EGFR-TKI treatment were included in this study from January 1, 2014 to December 31, 2021. Patients were randomly divided into training and validation cohorts in a ratio of 2:1. Radiomics features extracted from brain MRI were screened by least absolute shrinkage and selection operator (LASSO) algorithm. Logistic regression analysis and Cox proportional hazard regression analysis were used to screen clinical risk factors. Clinical (C), radiomics (R), and combined (C + R) nomograms were constructed in models predicting short-term efficacy and intracranial progression-free survival (iPFS), respectively. Calibration curves, Harrell's concordance index (C-index), and decision curve analysis (DCA) were used to evaluate the performance of models.

RESULTS

Overall response rate (ORR) was 57.3% and median iPFS was 12.67 months. The C + R nomograms were more effective. In the short-term efficacy model, the C-indexes of C + R nomograms in training cohort and validation cohort were 0.860 (0.820-0.901, 95%CI) and 0.843 (0.783-0.904, 95%CI). In iPFS model, the C-indexes of C + R nomograms in training cohort and validation cohort were 0.837 (0.751-0.923, 95%CI) and 0.850 (0.763-0.937, 95%CI).

CONCLUSION

The C + R nomograms were more effective in predicting EGFR-TKI efficacy of EGFR-mutant NSCLC patients with brain metastases than single clinical or radiomics nomograms.

Consideration of Optimal Evaluation Metrics for Internal Gross Tumor Dose Relevant to Tumor Response in Multi-fraction Stereotactic Radiosurgery of Brain Metastasis

Introduction In stereotactic radiosurgery (SRS) for brain metastasis (BM), the target dose inhomogeneity remains highly variable among modalities, irradiation techniques, and facilities, which can affect tumor response during and after multi-fraction SRS. Volumetric-modulated arcs (VMAs) can provide a concentrically-layered steep dose increase inside a gross tumor volume (GTV) boundary compared to dynamic conformal arcs. This study was conducted to review the optimal evaluation method for the internal GTV doses relevant to maximal response and local control, specifically to examine the significance of the doses 2 mm and 4 mm inside the GTV boundary in VMA-based SRS. Materials and methods This was a planning study for the clinical scenario of a single BM and targeted 25 GTVs of >0.50 cc, including eight spherical models with diameters of 10-45 mm and 17 clinical BMs (GTV: 0.72-44.33 cc). SRS plans were generated for each GTV using VMA with a 5-mm leaf-width multileaf collimator and the optimization that prioritized the steepness of the dose gradient outside the GTV boundary without any internal dose constraints. The dose prescription and evaluation were based on the GTV D V-0.01 cc, a minimum dose of GTV minus 0.01 cc. Two planning systems were compared for the GTV - 2 mm and GTV - 4 mm structures that were generated by equally reducing 2 mm and 4 mm from the GTV surface. The D eIIVs, a minimum dose of the irradiated isodose volume equivalent to the GTV - 2 mm and GTV - 4 mm, were compared to other common metrics. Results The GTV - 2 mm and GTV - 4 mm volumes differed significantly between the systems. In the spherical GTVs, the irradiated isodose surfaces of GTV D 80% and D 50% corresponded to 0.4-1.6 mm (<2 mm) and 1.0-4.6 mm inside the GTV boundary, respectively. In the 25 GTVs, the GTV - 2 mm coverage with the D eIIV varied from 83.7% to 98.2% (95-98% in 68% of the cases), while the GTV coverage with the GTV - 2 mm D eIIV was 20.2-75.9%. In the 23 GTVs of ≥1.26 cc, the GTV coverage with the GTV - 4 mm D eIIV varied from 1.9% to 55.6% (<50% in 87% of the cases). No significant difference was observed between the GTV D 50% and the GTV - 2 mm D eIIV, while the GTV - 4 mm D eIIV was significantly higher than the GTV D 50%. No significant correlations were observed between the GTV D 50% and the D eIIVs of the GTV - 2 mm and GTV - 4 mm. Conclusions The doses 2 mm and 4 mm inside a GTV have low correlations with the GTV D 50% and may be more relevant to maximal response and local control for SRS of BM. The D eIIV instead of the minimum dose of a fixed % coverage (e.g. D 98%) is suitable for reporting the doses 2 mm and 4 mm inside the GTV boundary in terms of avoiding the over- or under-coverage, with consideration to substantial variability in minus margin addition functions among planning systems. In VMA-based SRS with a steep dose gradient, the doses 2-4 mm inside a GTV decrease significantly as the GTV increases, which can attenuate the excessive dose exposure to the surrounding brain in a large BM due to the GTV shrinkage during multi-fraction SRS.

Appropriateness of Dose Attenuation Margin Outside the Gross Tumor Volume (GTV) in Volumetric-Modulated Arc-Based Radiosurgery for Brain Metastasis With the Steepest Dose Gradient Outside the GTV and Biologically Effective Dose 80 Gy to GTV Boundary

Introduction In stereotactic radiosurgery (SRS) for brain metastasis (BM), volumetric-modulated arcs (VMA) can provide a suitable dose distribution and efficient delivery, even with a widely available 5-mm leaf-width multileaf collimator (MLC). The planning optimization with affirmatively accepting internal high doses of a gross tumor volume (GTV) enhances the steepness of the dose gradient outside the GTV. However, an excessively steep dose falloff outside a GTV is susceptible to insufficient coverage of inherent irradiation uncertainties with the dose attenuation margin. This study was conducted to examine the appropriateness of dose attenuation margin outside a GTV in 5-mm MLC VMA-based SRS with a steep dose gradient and dose prescription with a biologically effective dose (BED) 80 Gy in various fractions to the GTV margin. Materials and methods This was a planning study for the clinical scenario of a single BM and targeted 28 GTVs, including nine sphere-shaped models with diameters of 5-45 mm and 19 clinical BMs (GTV 0.08-44.33 cc). SRS plans were generated for each GTV using 5-mm MLC VMA with an optimization that prioritized the steepness of dose falloff outside the GTV boundary without any internal dose constraints. A prescribed dose with the BED 80 Gy in 1-10 fraction(s) was assigned to the GTV D V-0.01 cc, a minimum dose of GTV minus 0.01 cc (D >95% for GTV >0.20 cc, D 95% for GTV ≤0.20 cc). The BED was based on the linear-quadratic formula with an alpha/beta ratio of 10 (BED10). Two planning systems were compared for the GTV + 2 mm structures that were generated by adding an isotropic 2-mm margin to the GTV. Results The GTV + 2 mm volumes differed significantly between the systems and further varied on the dose-volume histograms. The D V-0.05 cc, D 98%, and D 95% of the GTV + 2 mm were associated with substantial over- or under-coverages of the GTV + 2 mm, although the irradiated isodose volumes (IIVs) of the D 98% were closest to the GTV + 2 mm in general. The coverage values of the GTV + 2 mm with the minimum dose of the IIV equivalent to the GTV + 2 mm, D eIIV, were 93.3%-98.7% (≥95% in 26 cases). The GTV + 2 mm D eIIV relative to the GTV D V-0.01 cc was ≥81.9% (BED10 ≥60 Gy in ≤5 fractions) in 13 cases, while those were <69.8% (BED10 <48 Gy in ≤5 fractions) in four cases with the GTV of 0.33-1.77 cc. Conclusions A dose attenuation margin outside a GTV can be excessively steep for some small GTVs in 5-mm MLC VMA-based SRS with a steepest dose gradient and a BED10 80 Gy in ≤5 fractions to the GTV D V-0.01 cc, for which an adjustment of the too precipitous dose gradient is preferred to sufficiently cover relevant uncertainties. A GTV + 2 mm D eIIV with ≥95% coverage is more suitable for evaluating the appropriateness of dose attenuation outside the GTV than other common metrics with a fixed % coverage or D V-≤0.05 cc. Given the substantial variability in margin addition functions among planning systems, dose prescription to a margin-added GTV is unsuitable for ensuring uniform dose prescription.

Determinants of Symptomatic Intracranial Progression After an Initial Stereotactic Radiosurgery Course

Purpose

Clinical and imaging surveillance of patients with brain metastases is important after stereotactic radiosurgery (SRS) because many will experience intracranial progression (ITCP) requiring multidisciplinary management. The prognostic significance of neurologic symptoms at the time of ITCP is poorly understood.

Methods and Materials

This was a multi-institutional, retrospective cohort study from 2015 to 2020, including all patients with brain metastases completing an initial course of SRS. The primary outcome was overall survival (OS) by presence of neurologic symptoms at ITCP. OS, freedom from ITCP (FF-ITCP), and freedom from symptomatic ITCP (FF-SITCP) were assessed via Kaplan-Meier method. Cox proportional hazard models tested parameters impacting FF-ITCP and FF-SITCP.

Results

Among 1383 patients, median age was 63.4 years, 55% were female, and common primaries were non-small cell lung (49%), breast (15%), and melanoma (9%). At a median follow-up of 8.72 months, asymptomatic and symptomatic ITCP were observed in 504 (36%) and 194 (14%) patients, respectively. The majority of ITCP were distant ITCP (79.5%). OS was worse with SITCP (median, 10.2 vs 17.9 months, P < .001). SITCP was associated with clinical factors including total treatment volume (P = .012), melanoma histology (P = .001), prior whole brain radiation therapy (P = .003), number of brain metastases (P < .001), interval of 1 to 2 years from primary and brain metastasis diagnosis (P = .012), controlled extracranial disease (P = .042), and receipt of pre-SRS chemotherapy (P = .015). Patients who were younger and received post-SRS chemotherapy (P = .001), immunotherapy (P < .001), and targeted or small-molecule inhibitor therapy (P < .026) had better FF-SITCP.

Conclusions

In this cohort study of patients with brain metastases completing SRS, neurologic symptoms at ITCP is prognostic for OS. This data informs post-SRS surveillance in clinical practice as well as future prospective studies needed in the modern management of brain metastases.

Stereotactic radiotherapy of intracranial tumor beds on a ring-mounted Halcyon LINAC

PURPOSE

This study sought to evaluate the feasibility and efficacy of the Halcyon Ring Delivery System (RDS) for delivering stereotactic radiotherapy (SRT) treatments for intracranial tumors beds.

METHODS

Ten previously treated brain SRT patients for 30 Gy in five fractions with non-coplanar HyperArc plans on TrueBeam (6MV-FFF) were replanned on Halcyon (6MV-FFF) using the same number of arcs and Eclipse's AcurosXB dose engine. Plan quality evaluation metrics per SRT protocol included: PTV coverage, GTV dose (minimum and mean), target conformity indices (CI), heterogeneity index (HI), gradient index (GI), maximum dose 2 cm away from the PTV (D2cm), and doses to organs-at-risk (OAR). Additionally, patient-specific quality assurance (QA) results and beam-on-time (BOT) were analyzed.

RESULTS

The Halcyon RDS provided highly conformal SRT plans for intracranial tumor beds with similar dose to target. When benchmarked against clinically delivered HyperArc plans, target coverage, CI(s) and HI were statistically similar. The Halcyon plans saw no statistical difference in maximum OAR doses to the brainstem, spinal cord, and cochlea. Due to the machine's coplanar geometry, the Halcyon plans showed a decrease in optic pathway dose (0.75 Gy vs. 2.08 Gy, p = 0.029). Overall, Halcyon's coplanar geometry resulted in a larger GI (3.33 vs. 2.72, p = 0.008) and a larger D2cm (39.59% vs. 29.07%, p < 0.001). In this cohort, multiple cases had the PTV and the optic pathway in the same axial plane. In one such instance, the PTV was <2 cm away from the optic pathway but even at this close proximity OAR, Halcyon still adequately spared the optic pathway. Additionally, the Halcyon's geometry provided slightly larger amount of normal brain dose receiving 24.4 Gy (8.99 cc vs. 7.36 cc) and 28.8 Gy (2.9 cc vs. 2.5 cc), although statistically insignificant. The Halcyon plans achieved similar delivery accuracy, quantified by patient-specific QA results evaluated with a 2%/2 mm gamma criteria (99.42% vs. 99.70%). For both plans, independent Monte Carlo second checks calculation agreed within 1%. Average Halcyon BOT was slightly higher by 0.35 min (p = 0.045), however, due to the one-step patient set-up and verification overall estimated treatment times on Halcyon were lower compared to HyperArc treatments (7.61 min vs. 10.26 min, p < 0.001).

CONCLUSIONS

When benchmarked against clinically delivered HyperArc treatments, the Halcyon brain SRT plans provided similar plan quality and delivery accuracy but achieved faster overall treatment times. We have started treating select brain SRT patients on the Halcyon RDS for patients having tumor beds greater than 1 cm in diameter with the closest OAR distance of greater than 2 cm away from the target. We recommend other clinics to consider commissioning SRT treatments on their Halcyon systems-allowing including remote Halcyon-only clinics to provide exceptionally high-quality therapeutic brain SRT treatments to an otherwise underserved patient cohort.

Integrating Overall Survival and Tumor Control Probability Models to Predict Local Progression After Brain Metastasis Radiosurgery

Purpose

Stereotactic radiosurgery (SRS) for brain metastases is frequently prescribed to the maximum tolerated dose to minimize the probability of local progression. However, many patients die from extracranial disease prior to local progression and may not require maximally aggressive treatment. Recently, improvements in models of SRS tumor control probability (TCP) and overall survival (OS) have been made. We predicted that by combining models of OS and TCP, we could better predict the true risk of local progression after SRS than by using TCP modeling alone.

Methods and Materials

Records of patients undergoing SRS at a single institution were reviewed retrospectively. Using established TCP and OS models, for each patient, the probability of 1-year survival [p ( O S ) ] was calculated, as was the probability of 1-year local progression [p ( L P ) ]) for each treated lesion. Joint-probability was used to combine the models [p ( L P , O S ) = p ( L P ) * p ( O S ) ]. Analyses were conducted at the individual metastasis and whole-patient levels. Fine-Gray regression was used to model p ( L P ) or p ( L P , O S ) on the risk of local progression after SRS, with death as a competing risk.

Results

At the patient level, 1-year local progression was 0.08 (95% CI, 0.03-0.15), median p ( L P , O S ) was 0.13 (95% CI, 0.07-0.2), and median p ( L P ) was 0.29 (95% CI, 0.22-0.38). At the metastasis level, 1-year local progression was 0.02 (95% CI, 0.01-0.04), median p ( L P , O S ) was 0.05 (95% CI, 0.02-0.07), and median p ( L P ) was 0.10 (95% CI, 0.07-0.13). p ( L P , O S ) was found to be significantly associated with the risk of local progression at the patient level (P = .048) and metastasis level (P = .007); however, p ( L P ) was not (P = .16 and P = .28, respectively).

Conclusions

Simultaneous modeling of OS and TCP more accurately predicted local progression than TCP modeling alone. Better understanding which patients with brain metastases are at risk of local progression after SRS may help personalize treatment to minimize risk without sacrificing efficacy.

Growth speed of large brain metastases between diagnostic and radiosurgical planning MRI and predictors of rapid tumor growth

PURPOSE

We aimed to assess volumetric changes of large brain metastases (≥ 2 cm) between their diagnosis and planning for treatment with fractionated stereotactic radiation surgery (fSRS). Predictors of rapid tumor growth were also analyzed.

MATERIALS AND METHODS

One hundred nine patients harboring 126 large brain metastases were retrospectively evaluated. Tumor characteristics were evaluated on diagnostic magnetic resonance imaging (dMRI) and MRI performed when planning fSRS (pMRI). Average tumor growth rate and percentage growth rate were calculated. Predictors of rapid growth (percentage growth rate > 5%) were determined using multivariate logistic regression.

RESULTS

Both tumor diameter and volume were significantly larger on pMRI than on dMRI (P < 0.001). Median tumor percentage growth rate was 2.6% (range, - 10.8-43.3%). Eighty-eight tumors (70%) were slow-growing (percentage growth rate < 5%) and 38 (30%) grew rapidly (percentage growth rate ≥ 5%). Major peritumoral edema and no steroids were predictors of rapid tumor growth.

CONCLUSION

Large brain metastases can grow considerably between the time of diagnosis and the time of fSRS treatment planning. We recommend the time between dMRI and fSRS treatment initiation be as short as possible.

Fractionated stereotactic radiotherapy of intracranial postoperative cavities after resection of brain metastases - Clinical outcome and prognostic factors

Background and Purpose

After surgical resection of brain metastases (BM), radiotherapy (RT) is indicated. Postoperative stereotactic radiosurgery (SRS) reduces the risk of local progression and neurocognitive decline compared to whole brain radiotherapy (WBRT). Aside from the optimal dose and fractionation, little is known about the combination of systemic therapy and postoperative fractionated stereotactic radiotherapy (fSRT), especially regarding tumour control and toxicity.

Methods

In this study, 105 patients receiving postoperative fSRT with 35 Gy in 7 fractions performed with Cyberknife were retrospectively reviewed. Overall survival (OS), local control (LC) and total intracranial brain control (TIBC) were analysed via Kaplan-Meier method. Cox proportional hazards models were used to identify prognostic factors.

Results

Median follow-up was 20.8 months. One-year TIBC was 61.6% and one-year LC was 98.6%. Median OS was 28.7 (95%-CI: 16.9-40.5) months. In total, local progression (median time not reached) occurred in 2.0% and in 20.4% radiation-induced contrast enhancements (RICE) of the cavity (after median of 14.3 months) were diagnosed. Absence of extracranial metastases was identified as an independent prognostic factor for superior OS (p = <0.001) in multivariate analyses, while a higher Karnofsky performance score (KPS) was predictive for longer OS in univariate analysis (p = 0.041). Leptomeningeal disease (LMD) developed in 13% of patients.

Conclusion

FSRT after surgical resection of BM is an effective and safe treatment approach with excellent local control and acceptable toxicity. Further prospective randomized trials are needed to establish standardized therapeutic guidelines.

Stereotactic Radiosurgery for Patients with Brain Metastases from Hepatopancreaticobiliary Cancers

BACKGROUND

The role of stereotactic radiosurgery (SRS) for patients with brain metastases from hepatopancreaticobiliary (HPB) cancers has yet to be established. The authors present a single-institution experience of patients with HPB cancers who underwent SRS when their cancer spread to the brain.

METHODS

We surveyed our Gamma Knife SRS data base of 18,000 patients for the years 1987-2022. In total, 19 metastatic HPB cancer patients (13 male) with 76 brain metastases were identified. The median age at SRS was 61 years (range: 48-83). The primary cancer sites were hepatocellular carcinoma (HCC, 11 patients), cholangiocarcinoma (CCC, 2 patients), and pancreatic carcinoma (PCC, 6 patients). The median Karnofsky Performance Score (KPS) was 80 (range: 50-90). Two patients underwent pre-SRS whole-brain fractionated radiation therapy (WBRT) and eight patients underwent pre-SRS surgical resection. All SRS was delivered in single session. The median margin dose was 18 Gy (range: 15-20). The median cumulative tumor volume was 8.1 cc (range: 1.0-44.2).

RESULTS

The median patient overall survival (OS) after SRS was 7 months (range 1-79 months). Four patients had documented local tumor progression after SRS at a median time of 8.5 months (range: 2-15) between SRS and progression. Out of 76 treated tumors, 72 tumors exhibited local control. The local tumor control rate per patient was 78.9%. The local tumor control per tumor was 94.7%. Four patients developed new brain metastases at a median of 6.5 months (range: 2-17) after SRS. No patient experienced adverse radiation effects (AREs). At the last follow-up, 18 patients had died, all from systemic disease progression.

CONCLUSIONS

Metastatic spread to the brain from HPB cancers occurs late in the course of the primary disease. In this study, all deceased patients ultimately died from primary disease progression. SRS is a non-invasive strategy that maximally preserves quality of life, and our results reported favorable outcomes compared to the existing literature. SRS should be considered as one of the primary management strategies for patients with brain metastatic spread from HPB cancer.

Proposal of an Alternative Near-Minimum Isodose Surface DV-0.01 cc Equally Minimizing Gross Tumor Volume Below the Relevant Dose as the Basis for Dose Prescription and Evaluation of Stereotactic Radiosurgery for Brain Metastases

Introduction In stereotactic radiosurgery (SRS) for brain metastasis (BM), the prescribed dose is generally reported as a minimum dose to cover a specific percentage (e.g. D98%) of the gross tumor volume (GTV) with or without a margin or an unspecified intended marginal dose to the GTV boundary. In dose prescription to a margin-added planning target volume (PTV), the GTV marginal dose is likely variable and unclear. This study aimed to reveal major flaws of dose prescription to a fixed % coverage of a target volume (TV), such as GTV D98% or PTV D95%, and to propose an alternative. Materials and methods Seven quasi-spherical models with volumes ranging from 1.00 to 15.00 cc were assumed as GTVs. The GTVs and the volumes generated by adding isotropic 1- and 2-mm margins to the GTV boundaries (GTV + 1 and 2 mm) were used for SRS planning, dose prescription, and evaluation. Volumetric-modulated arcs with a 5-mm leaf-width multileaf collimator were used to optimize each SRS plan to ensure the steepest dose gradient outside each TV boundary. In dose prescription to the GTV D98%, 0.02-0.3 cc of the GTV is below the prescribed dose, and the volume increases with larger GTVs. The volume below the prescribed dose should be less than the equivalent of a 3-mm-diameter lesion, i.e. 0.01 cc. Therefore, DV-0.01 cc was defined as an alternative near-minimum dose for which the TV below a relevant dose is less than 0.01 cc. Four different dose prescriptions, including the GTV DV-0.01 cc, were compared using specific doses in 1, 3, and 5 fractions, equivalent to 80, 60, and 50 Gy, respectively, as biologically effective doses (BEDs) to the boundaries of GTV, GTV + 1 mm, and GTV + 2 mm, respectively. Results Dose prescription to the GTV DV-0.01 cc corresponds to 95.0, 98.0, and 99.0-99.93% coverages for the GTV of 0.20, 0.50, and 1.00-15.00 cc, respectively. The GTV DV-0.01 cc varied substantially and decreased significantly as the GTV increased in dose prescriptions to the GTV D98%, GTV + 1 mm D95%, and GTV + 2 mm D95%. The GTV + 2 mm DV-0.01 cc increased significantly as the GTV increased, except for the dose prescription to the GTV + 2 mm D95% with a decreasing tendency. When comparing BED-based specific dose prescriptions, dose prescription to the GTV DV-0.01 cc was optimal in terms of the following: 1) consistency of the near-minimum dose of GTV; 2) the highest BED at 2 mm outside the GTV, except for 1.00 cc GTV, and the rational increase with increasing GTV; and 3) the highest BED at 2 mm inside the GTV. In dose prescription with the BED of 80 Gy in 1 fraction and 5 fractions to the GTV DV-0.01 cc, the GTV limits were ≤1.40 and ≤8.46 cc, respectively, in order for the irradiated isodose volume not to exceed the proposed thresholds for minimizing the risk of brain radionecrosis. Conclusions Dose prescription to a fixed % coverage of a GTV with or without a margin leads to the substantially varied near-minimum dose at the GTV boundary, which significantly decreases with increasing GTV. Alternatively, GTV DV-0.01 cc with a variable coverage (D>95%) for >0.20 cc GTV and fixed D95% for ≤0.20 cc GTV is recommended as the basis for dose prescription and evaluation, along with supplemental evaluation of the marginal dose of the GTV plus a margin (e.g. GTV + 2 mm) to demonstrate the appropriateness of dose attenuation outside the GTV boundary.

DEGRO guideline for personalized radiotherapy of brain metastases and leptomeningeal carcinomatosis in patients with breast cancer

PURPOSE

The aim of this review was to evaluate the existing evidence for radiotherapy for brain metastases in breast cancer patients and provide recommendations for the use of radiotherapy for brain metastases and leptomeningeal carcinomatosis.

MATERIALS AND METHODS

For the current review, a PubMed search was conducted including articles from 01/1985 to 05/2023. The search was performed using the following terms: (brain metastases OR leptomeningeal carcinomatosis) AND (breast cancer OR breast) AND (radiotherapy OR ablative radiotherapy OR radiosurgery OR stereotactic OR radiation).

CONCLUSION AND RECOMMENDATIONS

Despite the fact that the biological subtype of breast cancer influences both the occurrence and relapse patterns of breast cancer brain metastases (BCBM), for most scenarios, no specific recommendations regarding radiotherapy can be made based on the existing evidence. For a limited number of BCBM (1-4), stereotactic radiosurgery (SRS) or fractionated stereotactic radiotherapy (SRT) is generally recommended irrespective of molecular subtype and concurrent/planned systemic therapy. In patients with 5-10 oligo-brain metastases, these techniques can also be conditionally recommended. For multiple, especially symptomatic BCBM, whole-brain radiotherapy (WBRT), if possible with hippocampal sparing, is recommended. In cases of multiple asymptomatic BCBM (≥ 5), if SRS/SRT is not feasible or in disseminated brain metastases (> 10), postponing WBRT with early reassessment and reevaluation of local treatment options (8-12 weeks) may be discussed if a HER2/Neu-targeting systemic therapy with significant response rates in the central nervous system (CNS) is being used. In symptomatic leptomeningeal carcinomatosis, local radiotherapy (WBRT or local spinal irradiation) should be performed in addition to systemic therapy. In patients with disseminated leptomeningeal carcinomatosis in good clinical condition and with only limited or stable extra-CNS disease, craniospinal irradiation (CSI) may be considered. Data regarding the toxicity of combining systemic therapies with cranial and spinal radiotherapy are sparse. Therefore, no clear recommendations can be given, and each case should be discussed individually in an interdisciplinary setting.

The Role of Stereotactic Radiosurgery in Patients With Brain Metastases From Colorectal Cancers

BACKGROUND AND OBJECTIVES

The role of stereotactic radiosurgery (SRS) in patients with brain metastases (BMs) from colorectal cancers (CRCs) has not been established. The authors present a single-institution experience of patients with CRC who underwent SRS with metastatic brain spread.

METHODS

We retrospectively analyzed 111 patients with metastatic CRC (64 female, 57.7%), with 449 BMs treated with Gamma Knife SRS between 2000 and 2022. The median age during SRS was 63 years (range: 28-86), and the median Karnofsky Performance Scale was 80 (range: 60-100). The primary sites were colon (85 patients, 76.6%) and rectal (26 patients, 23.4%). Three patients underwent hypofractionated SRS (3 sessions) with a median margin dose of 27 Gy (range: 27-30). All other patients underwent single-session SRS with a median margin dose of 18 Gy (range: 13-20).

RESULTS

The median patient survival after SRS was 7 months (range: 1-174). Ninety-eight (88.3%) patients expired at last follow-up and 15 patients (15.3%) died related to progressive intracranial disease. A Karnofsky Performance Scale of <80 at SRS presentation ( P = .02, hazard ratio [HR]: 0.6, 95% CI: 0.4-0.9) and no previous surgical resection ( P < .01, HR: 0.4, 95% CI: 0.3-0.7) were associated with inferior overall survival using multivariate analysis. Seventeen patients (15.3%) had documented local tumor progression after SRS, at a median time of 7 months (range: 3-34) between SRS and progression. Twenty-six patients (23.4%) developed new BMs at a median of 5 months (range: 2-26) between SRS and new tumor detection. Less than three BMs at SRS presentation ( P = .02, HR: 2.6, 95% CI: 1.2-5.6) were associated with better distant tumor control on multivariate analysis. The incidence of adverse radiation effects was 5.4%.

CONCLUSION

SRS effectively controls BMs from CRC with low risk of treatment-related toxicity. During follow-up, the development of additional metastases can be safely treated by repeat SRS.

Clinical application of an institutional fractionated stereotactic radiosurgery (FSRS) program for brain metastases delivered with MRIdianⓇ BrainTx™

Single-fraction stereotactic radiosurgery (SRS) or fractionated SRS (FSRS) are well established strategies for patients with limited brain metastases. A broad spectrum of modern dedicated platforms are currently available for delivering intracranial SRS/FSRS; however, SRS/FSRS delivered using traditional CT-based platforms relies on the need for diagnostic MR images to be coregistered to planning CT scans for target volume delineation. Additionally, the on-board image guidance on traditional platforms yields limited inter-fraction and intra-fraction real-time visualization of the tumor at the time of treatment delivery. MR Linacs are capable of obtaining treatment planning MR and on-table MR sequences to enable visualization of the targets and organs-at-risk and may subsequently help identify anatomical changes prior to treatment that may invoke the need for on table treatment adaptation. Recently, an MR-guided intracranial package (MRIdian A3i BrainTxTM) was released for intracranial treatment with the ability to perform high-resolution MR sequences using a dedicated brain coil and cranial immobilization system. The objective of this report is to provide, through the experience of our first patient treated, a comprehensive overview of the clinical application of our institutional program for FSRS adaptive delivery using MRIdian's A3i BrainTx system-highlights include reviewing the imaging sequence selection, workflow demonstration, and details in its delivery feasibility in clinical practice, and dosimetric outcomes.

Single-Fraction Versus Fractionated Preoperative Radiosurgery for Resected Brain Metastases: A PROPS-BM International Multicenter Cohort Study

PURPOSE

Preoperative stereotactic radiosurgery (SRS) is a feasible alternative to postoperative SRS for resected brain metastases (BM). Most reported studies of preoperative SRS used single-fraction SRS (SF-SRS). The goal of this study was to compare outcomes and toxicity of preoperative SF-SRS with multifraction (3-5 fractions) SRS (MF-SRS) in a large international multicenter cohort (Preoperative Radiosurgery for Brain Metastases-PROPS-BM).

METHODS AND MATERIALS

Patients with BM from solid cancers, of which at least 1 lesion was treated with preoperative SRS followed by planned resection, were included from 8 institutions. SRS to synchronous intact BM was allowed. Exclusion criteria included prior or planned whole brain radiation therapy. Intracranial outcomes were estimated using cumulative incidence with competing risk of death. Propensity score matched (PSM) analyses were performed.

RESULTS

The study cohort included 404 patients with 416 resected index lesions, of which SF-SRS and MF-SRS were used for 317 (78.5%) and 87 patients (21.5%), respectively. Median dose was 15 Gy in 1 fraction for SF-SRS and 24 Gy in 3 fractions for MF-SRS. Univariable analysis demonstrated that SF-SRS was associated with higher cavity local recurrence (LR) compared with MF-SRS (2-year: 16.3% vs 2.9%; P = .004), which was also demonstrated in multivariable analysis. PSM yielded 81 matched pairs (n = 162). PSM analysis also demonstrated significantly higher rate of cavity LR with SF-SRS (2-year: 19.8% vs 3.3%; P = .003). There was no difference in adverse radiation effect, meningeal disease, or overall survival between cohorts in either analysis.

CONCLUSIONS

Preoperative MF-SRS was associated with significantly reduced risk of cavity LR in both the unmatched and PSM analyses. There was no difference in adverse radiation effect, meningeal disease, or overall survival based on fractionation. MF-SRS may be a preferred option for neoadjuvant radiation therapy of resected BMs. Additional confirmatory studies are needed. A phase 3 randomized trial of single-fraction preoperative versus postoperative SRS (NRG-BN012) is ongoing (NCT05438212).

Brain diffusion MRI biomarkers after oncology treatments

In addition to providing a measurement of the tumor's size and dimensions, magnetic resonance imaging (MRI) provides excellent noninvasive radiographic detection of tumor location. The MRI technique is an important modality that has been shown to be useful in the prognosis, diagnosis, treatment planning, and evaluation of response and recurrence in solid cancers. Diffusion-weighted imaging (DWI) is an imaging technique that quantifies water mobility. This imaging approach is good for identifying sub-voxel microstructure of tissues, correlates with tumor cellularity, and has been proven to be valuable in the early assessment of cytotoxic treatment for a variety of malignancies. Diffusion tensor imaging (DTI) is an MRI method that assesses the preferred amount of water transport inside tissues. This enables precise measurements of water diffusion, which changes according to the direction of white matter fibers, their density, and myelination. This measurement corresponds to some related variables: fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), axial diffusivity (AD), and others. DTI biomarkers can detect subtle changes in white matter microstructure and integrity following radiation therapy (RT) or chemoradiotherapy, which may have implications for cognitive function and quality of life. In our study, these indices were evaluated after brain chemoradiotherapy.

CNN-based multi-modal radiomics analysis of pseudo-CT utilization in MRI-only brain stereotactic radiotherapy: a feasibility study

BACKGROUND

Pseudo-computed tomography (pCT) quality is a crucial issue in magnetic resonance image (MRI)-only brain stereotactic radiotherapy (SRT), so this study systematically evaluated it from the multi-modal radiomics perspective.

METHODS

34 cases (< 30 cm³) were retrospectively included (2021.9-2022.10). For each case, both CT and MRI scans were performed at simulation, and pCT was generated by a convolutional neural network (CNN) from planning MRI. Conformal arc or volumetric modulated arc technique was used to optimize the dose distribution. The SRT dose was compared between pCT and planning CT with dose volume histogram (DVH) metrics and gamma index. Wilcoxon test and Spearman analysis were used to identify key factors associated with dose deviations. Additionally, original image features were extracted for radiomic analysis. Tumor control probability (TCP) and normal tissue complication probability (NTCP) were employed for efficacy evaluation.

RESULTS

There was no significant difference between pCT and planning CT except for radiomics. The mean value of Hounsfield unit of the planning CT was slightly higher than that of pCT. The Gadolinium-based agents in planning MRI could increase DVH metrics deviation slightly. The median local gamma passing rates (1%/1 mm) between planning CTs and pCTs (non-contrast) was 92.6% (range 63.5-99.6%). Also, differences were observed in more than 85% of original radiomic features. The mean absolute deviation in TCP was 0.03%, and the NTCP difference was below 0.02%, except for the normal brain, which had a 0.16% difference. In addition, the number of SRT fractions and lesions, and lesion morphology could influence dose deviation.

CONCLUSIONS

This is the first multi-modal radiomics analysis of CNN-based pCT from planning MRI for SRT of small brain lesions, covering dosiomics and radiomics. The findings suggest the potential of pCT in SRT plan design and efficacy prediction, but caution needs to be taken for radiomic analysis.

Perfusion MRI in the evaluation of brain metastases: current practice review and rationale for study of baseline MR perfusion imaging prior to stereotactic radiosurgery (STARBEAM-X)

Stereotactic radiosurgery is an established focal treatment for brain metastases with high local control rates. An important side-effect of stereotactic radiosurgery is the development of radionecrosis. On conventional MR imaging, radionecrosis and tumour progression often have similar appearances, but have contrasting management approaches. Perfusion MR imaging is often used in the post-treatment setting in order to help distinguish between the two, but image interpretation can be fraught with challenges.Perfusion MR plays an established role in the baseline and post-treatment evaluation of primary brain tumours and a number of studies have concentrated on the value of perfusion imaging in brain metastases. Of the parameters generated, relative cerebral blood volume is the most widely used variable in terms of its clinical value in differentiating between radionecrosis and tumour progression. Although it has been suggested that the relative cerebral blood volume tends to be elevated in active metastatic disease following treatment with radiosurgery, but not with treatment-related changes, the literature available on interpretation of the ratios provided in the context of defining tumour progression is not consistent.This article aims to provide an overview of the role perfusion MRI plays in the assessment of brain metastases and introduces the rationale for the STARBEAM-X study (Study of assessment of radionecrosis in brain metastases using MR perfusion extra imaging), which will prospectively evaluate baseline perfusion imaging in brain metastases. We hope this will allow insight into the vascular appearance of metastases from different primary sites, and aid in the interpretation of post-treatment perfusion imaging.

The Impact of Immune Checkpoint Inhibition on the Risk of Radiation Necrosis Following Stereotactic Radiotherapy for Metastatic Brain Cancer

Purpose/objective Forty percent of cancer patients develop brain metastases (BM) and are often treated with stereotactic radiation (SRS/SRT). Checkpoint inhibitor (CI) use is suspected of increasing the risk of radiation necrosis (RN). Our aim is to determine whether treatment with CI is associated with an increased risk of RN in BM patients treated with SRS/SRT. Methods We retrospectively identified the medical records of BM patients treated with SRS/SRT between 1/2017 and 12/2021 using an institutional database. RN was defined by MRI imaging read by neuroradiologists and/or surgical pathology. V12GY of patients with and without RN was compared using the Mann-Whitney test. The chi-square test was used to see if RN was associated with CI use, histology, particular CI agent used, > 1 course SRS/SRT, SRS/SRT dose, chemotherapy, whole brain radiotherapy (WBRT), age, or sex. Results Two hundred and fifty-nine patients treated with 455 courses of SRS/SRT were analyzed. The most common primary histologies were lung 56% (N=146), breast 14% (N= 37), melanoma 9% (N=24), and renal cancer 7% (N=18). A total of 53.8% (N = no. of patients) were treated with CI. The overall rate of any RN was 21.8% (N=27) in the CI group compared to 14.8% (N=141) in the non-CI group (p=0.174). Mean V12Gy was 15.525 cc and 9.419 cc in patients with and without RN (p=0.02768). Mean number of SRS/SRT courses was 2 and 1.53 for patients with and without RN, and >1 course of SRS/SRT was a predictor of RN (p <0.01). Other features analyzed were not significant. Conclusion RN was higher in the BM patients treated with SRS/SRT receiving CI compared to non-CI patients (21.8%, N=27, versus 14.6%, N= 16), but failed to reach statistical significance. V12Gy and > 1 course of SRS/SRT was associated with RN. Caution should be taken in treating patients with SRS/SRT and CI there might be an increased risk of RN.

Biomedical advances and future prospects of high-precision three-dimensional radiotherapy and four-dimensional radiotherapy

Biomedical advances of external-beam radiotherapy (EBRT) with improvements in physical accuracy are reviewed. High-precision (±1 mm) three-dimensional radiotherapy (3DRT) can utilize respective therapeutic open doors in the tumor control probability curve and in the normal tissue complication probability curve instead of the one single therapeutic window in two-dimensional EBRT. High-precision 3DRT achieved higher tumor control and probable survival rates for patients with small peripheral lung and liver cancers. Four-dimensional radiotherapy (4DRT), which can reduce uncertainties in 3DRT due to organ motion by real-time (every 0.1-1 s) tumor-tracking and immediate (0.1-1 s) irradiation, have achieved reduced adverse effects for prostate and pancreatic tumors near the digestive tract and with similar or better tumor control. Particle beam therapy improved tumor control and probable survival for patients with large liver tumors. The clinical outcomes of locally advanced or multiple tumors located near serial-type organs can theoretically be improved further by integrating the 4DRT concept with particle beams.

Dose-effect relationship of linear accelerator based stereotactic radiotherapy for brain metastases

OBJECTIVE

The purpose of this study is to reveal the dose-effect relationship of linear accelerator (LINAC)-based stereotactic radiotherapy (SRT) in patients with brain metastases (BM).

MATERIALS AND METHODS

The PubMed, Cochrane, and Web of Science databases were used to identify studies that reported local tumour control after LINAC-based SRT in patients with BMs. Studies of other approaches that could affect local tumour control, such as whole brain radiotherapy, targeted therapy, and immunotherapy, were excluded from the dose-effect relationship analysis. Data extracted included patient and treatment characteristics and tumour local control. Probit model in XLSTAT 2016 was used for regression analysis, and P < 0.05 was set as the statistically significant level.

RESULTS

After literature screening, 19 eligible studies involving 1523 patients were included in the probit model regression analysis. There was no significant dose-effect relationship between nominal BED10 and peripheral BED10 versus 12-month local control probability. There were significant dose effect relationships between the centre BED10 and the average BED10 versus the 12-month local control probability, with P values of 0.015 and 0.011, respectively. According to the model, the central BED10 and the average BED10 corresponding to probabilities of 90% 12-month local control were 109.2 GyBED10 (95% confidence interval (CI): 88.7-245.9 GyBED10) and 87.8 GyBED10 (95% CI: 74.3-161.5 GyBED10), respectively. A 12-month local control rate of 86.9% (95% CI: 81.7-89.7%) and 85.5% (95% CI: 81.2-89.2%) can be expected at a centre BED10 of 80 Gy and an average BED10 of 60 Gy, respectively.

CONCLUSION

For patients with BM treated with LINAC-based SRT, more attention should be given to the central and average doses of PTV. A clear definition of the dose prescription should be established to ensure the effectiveness and comparability of treatment.

Nineteen-Month Immunity to Adverse Radiation Effects Following 5-Fraction Re-radiosurgery With 43.6 Gy for Local Progression After Prior 3-Fraction Radiosurgery for Brain Metastasis From Pan-Negative Lung Adenocarcinoma

Clinical management of patients with local control failure following stereotactic radiosurgery (SRS) for brain metastasis (BM) can be frequently challenging. Re-irradiation with multi-fraction (fr) SRS by using a biological effective dose of ≥80 Gy, based on the linear-quadratic formula with an alpha/beta ratio of 10 (BED10), can be an efficacious option for such a scenario with the BED10 of <80 Gy. However, its long-term safety beyond one year remains unclear. In this report, we describe the case of a patient with a single metachronous BM from lung adenocarcinoma (LAC), without major genetic alterations, in which re-SRS with 43.6 Gy/5 fr (BED10 81.6 Gy) for local progression, following prior 3-fr SRS of the BM, resulted in sustained regression without any local adverse radiation effects (AREs) for 19 months. The BM with a gross tumor volume (GTV) of 1.12 cm3 in the left parietal lobe was initially treated with SRS of 27 Gy/3 fr (50% isodose). Despite steroid administration for nivolumab-induced bullous pemphigoid associated with transient elevation of tumor markers, the BM showed local progression with T1/T2 matching at 38.3 and eight months after SRS and discontinuation of nivolumab, respectively. In the 5-fr re-SRS, 99% of the GTV (1.18 cm3) was covered with 43.6 Gy (63% isodose). However, along with the thoracic disease progression, multiple new BMs developed 15.5 months after the re-SRS, for which volumetric-modulated arc-based whole brain radiotherapy (WBRT) was administered, with simultaneously integrated boosts to 17 lesions and moderate dose attenuation in the pre-irradiated region. However, concurrent administration of gemcitabine and WBRT might have led to persistent severe anorexia for 2.5 months. The patient died 10.8 years after the initial chemotherapy. The relatively small GTV with the superficial location may have rendered the re-irradiated region immune to AREs after the high BED10 re-SRS. Long-term survival can be achieved by chemoimmunotherapy in patients with pan-negative LAC, with limited systemic metastases who are unfit for targeted agents. Therefore, SRS for limited BMs in such scenarios should aim for complete local tumor eradication beyond a partial response in either a first-line or re-irradiation setting.