Single-Fraction Versus Multifraction (3 × 9 Gy) Stereotactic Radiosurgery for Large (>2 cm) Brain Metastases: A Comparative Analysis of Local Control and Risk of Radiation-Induced Brain Necrosis

Stereotactic Radiosurgery Dose Reduction for Melanoma Brain Metastases Patients on Immunotherapy or Target Therapy: A Single-Center Experience

BACKGROUND AND OBJECTIVES

Better local control but higher rates of adverse radiation events (ARE) have been reported when combining American Society for Radiation Oncology (ASTRO)-guideline-suggested dose (SD) stereotactic radiosurgery (SRS) with immunotherapy or targeted therapy for melanoma brain metastases. The objective of this study is to explore the efficacy and safety of lower prescription doses compared with ASTRO guidelines for single-fraction SRS for patients with melanoma metastases who are concurrently receiving immunotherapy or targeted therapy.

METHODS

We conducted a retrospective, single-center study on 194 patients who underwent SRS between 2009 and 2022. After propensity score matching, 71 patients with 292 metastases were included in the ASTRO-SD (20-24 Gy for <2 cm, 18 Gy for ≥2 to <3 cm) group and 33 patients with 292 metastases in the reduced dose (RD, <20 Gy for <2 cm, <18 Gy for ≥2 to <3 cm) group.

RESULTS

The median diameter (5.4 vs 5.2 mm, P = .6), prescription volume (0.2 vs 0.2 cm 3 , P = .2), and radiographic follow-up (11 vs 12 months, P = .2) were similar in the 2 groups. The cumulative incidence of progressing metastases was significantly higher in the SD compared with the RD group ( P = .018). Higher prescription volumes and ASTRO-suggested radiation doses were associated with local progression in multivariable analysis. Radiographic AREs were significantly more common in the SD compared with the RD group (8.6% vs 3.1%, P = .005). BRAF and other tyrosine kinase inhibitors' concurrent use, higher prescription volumes, and ASTRO-suggested radiation doses were associated with an increased risk of radiographic ARE.

CONCLUSION

This study provides evidence that RD SRS could offer reduced toxicity rates, while maintaining high local control as compared with the current guideline-SDs for the treatment of melanoma 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.

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.

Analysis of the impact of rotation error on PTV margins in multiple brain metastases fractionated stereotactic radiotherapy based on single-isocenter multi-target technique

Background

Rotational error cannot be overlooked in single-isocenter multi-target (SIMT) stereotactic radiotherapy. This retrospective study aimed to evaluate the treatment accuracy of linear accelerator-based fractionated stereotactic radiotherapy (FSRT) using SIMT non-coplanar volumetric modulated arc therapy (VMAT) in patients with multiple brain metastases. We explored the impact of rotational error on planning target volume (PTV) margins, providing clinical evidence for the selection of appropriate PTV margin values.

Methods

A total of 161 patients with multiple brain metastases (733 treatments; actual clinical PTV margins ranged from 1~2 mm) were included. Theoretical PTV margins were calculated based on the Van Herk and Jenghwa Chang formulas. We analyzed the influence of the distance from each target to the treatment isocenter, rotational errors, and PTV margin on treatment outcomes. Additionally, individualized PTV margins for each patient were calculated using the Jenghwa Chang formula and patients were divided into subgroups according to a 2-mm threshold for further analysis.

Results

The mean residual translational setup errors ranged from -0.04~0.01 mm, and rotational setup errors ranged from 0.15°~0.49°, both within acceptable limits. According to the Van Herk formula, required margins in posterior-anterior, superior-inferior, and right-left directions were 1.44 mm, 1.68 mm, and 1.78 mm, respectively. By incorporating both translational and rotational errors using the Jenghwa Chang formula, the comprehensive margin ranged from 1.69~1.79 mm (calculated based on the 95% confidence interval of distances from targets to isocenter). Additionally, when the mean distance from all targets to their respective treatment isocenters was 30.62 mm, the required margin calculated solely for translational errors using the Jenghwa Chang formula was 1.23 mm; if rotational errors were neglected, target coverage probability would decrease from 95% to 73%. Further subgroup analysis showed that 25 patients whose individualized theoretical margins exceeded 2 mm tended to experience worse outcomes compared to others, including intracranial local failure (ILF, defined as lesion progression within the previously irradiated intracranial region during follow-up; 32.00% vs. 22.29%, P = 0.32), one-year local control (64.00% vs. 65.44%, P = 0.89), and one-year intracranial progression-free survival (iPFS, 44.00% vs. 51.45%, P = 0.85). However, these differences did not reach statistical significance.

Conclusion

This study confirms that the SIMT non-coplanar VMAT technique ensures treatment accuracy for FSRT in multiple brain metastases. Rotational errors reduce dose coverage, and a minimum safety margin of 1.79 mm is recommended to ensure tumor coverage and reduce local failure, providing a basis for future treatment optimization.

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.

Investigation of Prevalence, Survival, and Molecular Type of Breast Cancer Patients with Brain Metastases

Background

This study aims to investigate the factors associated with breast cancer brain metastasis (BCBM) in individuals suffering from breast cancer (BC).

Materials and Methods

This cross-sectional study conducted on 200 patients with metastatic breast cancer (MBC) including 52 brain and 148 other organ metastases. The demographic, medical, clinical, laboratory, and therapeutic approach characteristics were compared between the groups.

Results

Headache (61.5%), weakness and lethargy (26.9%), dizziness (15.4%), blurred vision/blindness (15.4%), and convulsions (15.4%) were the major initial symptoms of BCBM. Radiotherapy (71.2%), injectable (34.6%), and oral chemotherapy (26.9%) were the major applied therapeutic strategies to manage brain metastasis (BM). The overall survival of the patients from cancer diagnosis to death accounted for 33 months (95%CI: 27.52-38.47), while this period after BM diagnosis was limited to 6 months (95%CI: 5.15-6.84). The rate of hormone therapy was remarkably higher among the metastasis in other organs than the brain (P value = 0.005), while targeted therapy was performed in higher rates for BM (P value = 0.001). The evaluation of BC-related tumor markers revealed that human epidermal growth factor 2 (HER2) (P value < 0.001) positivity was remarkably higher among BCBM, while positive estrogen receptor (ER) (P value = 0.004) and progesterone receptor (PR) (P value = 0.013) were statistically more in the other group.

Conclusion

Based on the findings of this study, the BC patients with BM had a remarkable short survival, had a higher rate of perineural invasion, and were mostly positive for HER2. Radiotherapy, chemotherapy, and surgery were the most common approaches to these patients.

Total brain dose estimation in single-isocenter-multiple-targets (SIMT) radiosurgery via a novel deep neural network with spherical convolutions

BACKGROUND AND PURPOSE

Accurate prediction of normal brain dosimetric parameters is crucial for the quality control of single-isocenter multi-target (SIMT) stereotactic radiosurgery (SRS) treatment planning. Reliable dose estimation of normal brain tissue is one of the great indicators to evaluate plan quality and is used as a reference in clinics to improve potentially SIMT SRS treatment planning quality consistency. This study aimed to develop a spherical coordinate-defined deep learning model to predict the dose to a normal brain for SIMT SRS treatment planning.

METHODS

By encapsulating the human brain within a sphere, 3D volumetric data of planning target volume (PTVs) can be projected onto this geometry as a 2D spherical representation (in azimuthal and polar angles). A novel deep learning model spherical convolutional neural network (SCNN) was developed based on spherical convolution to predict brain dosimetric evaluators from spherical representation. Utilizing 106 SIMT cases, the model was trained to predict brain V50%, V60%, and V66.7%, corresponding to V10Gy and V12Gy, as key dosimetric indicators. The model prediction performance was evaluated using the coefficient of determination (R2), mean absolute error (MAE), and mean absolute percentage error (MAPE).

RESULTS

The SCNN accurately predicted normal brain dosimetric values from the modeled spherical PTV representation, with R2 scores of 0.92 ± 0.05/0.94 ± 0.10/0.93 ± 0.09 for V50%/V60%/V66.7%, respectively. MAEs values were 1.94 ± 1.61 cc/1.23 ± 0.98 cc/1.13 ± 0.99 cc, and MAPEs were 19.79 ± 20.36%/20.79 ± 21.07%/21.15 ± 22.24%, respectively.

CONCLUSIONS

The deep learning model provides treatment planners with accurate prediction of dose to normal brain, enabling improved consistency in treatment planning quality. This method can be extended to other brain-related analyses as an efficient data dimension reduction method.

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.

Hypofractionated stereotactic radiotherapy using coplanar VMAT for single small brain metastasis: dosimetric analysis and clinical outcomes

Purpose

To evaluate the dosimetric parameters and clinical outcomes of hypofractionated stereotactic radiotherapy (HSRT) for small brain metastases [BMs; planning target volume (PTV) ≤ 4 cm3) via coplanar volumetric modulated arc therapy (C-VMAT).

Methods

Between March 2019 and February 2023, 68 patients with a single BM treated with Linac-based HSRT (24-39 Gy in three fractions) via C-VMAT and a 3-mm PTV margin were enrolled in this retrospective analysis. A frameless head-neck-shoulder thermoplastic mask, whose immobilization accuracy is inferior to that of specialized mask fixation systems, was used to immobilize patients. Dosimetric parameters and clinical outcomes were evaluated.

Results

C-VMAT provided clinically satisfactory treatment plans, with median gradient index, conformity index, homogeneity index, and PTV coverage values of 4.30, 1.05, 1.28, and 98%, respectively. The median volumes of normal brain tissue receiving 18 Gy, 21 Gy, and 23 Gy were 7.29 cm3, 5.33 cm3, and 4.40 cm3, respectively. High delivery accuracy was observed, with a gamma passing rate ≥90% for all plans. As of June 2023, the median follow-up time was 9.1 months. The intracranial objective response rate and disease control rate were 64% and 96%, respectively. The median intracranial progression-free survival was 26.9 (95% CI, 12.7-41.1) months. The 1- and 2-year local control (LC) rates were 91.5% (95% CI, 80.1%-100%) and 83.2% (95% CI, 64.6%-100%), respectively. The 1- and 2-year intracranial control rates were 70.9% (95% CI, 55.2%-86.6%) and 51.2% (95% CI, 32.6%-69.8%), respectively. Only four irradiated lesions progressed at the end of follow-up. The cerebral radiation necrosis rate of all patients was 7.4%.

Conclusion

C-VMAT HSRT combined with a 3-mm PTV margin is an effective and safe treatment modality for small BMs.

Single- versus multi-fraction spine stereotactic radiosurgery (ALL-STAR) for patients with spinal metastases: a randomized phase III trial protocol

BACKGROUND

For patients with spine metastases, stereotactic radiosurgery (SRS) provides excellent local control and pain response. Despite increasing use of this treatment modality, there is no consensus on the optimal dose and fractionation of spine SRS for efficacy and toxicity. We have initiated a single-center phase III randomized trial that compares two dose regimens with similar biological equivalent dose (BED) to determine the isolated effect of SRS fractionation on local control.

METHODS

Patients with one to three cervical, thoracic, or lumbar spine metastases spanning no more than two contiguous vertebral levels in need of radiation will be eligible for enrollment. Patients will be assigned 1:1 to receive either 22 Gy in 1 fraction or 28 Gy in 2 fractions. Biased coin randomization will be used to randomly assign patients while balancing the following stratifying variables between the two treatment arms at baseline: gastrointestinal histology (yes/no), paraspinal tissue extension (yes/no), epidural compression (low-/high-grade), and number of sites treated (one to three). The primary endpoint is one-year local control, defined per Spine Response Assessment in Neuro-Oncology (SPINO) criteria. The secondary endpoints include patient-reported health-related quality of life (HRQOL), pain associated with the treated site, vertebral compression fracture (VCF), and two-year local control. Patients will be followed for these outcomes at one to two weeks, one month, three months, and six months after treatment, and every six months thereafter until 24 months after treatment. While on the study, patients will receive routine co-interventions as clinically indicated.

DISCUSSION

The studies published thus far comparing the single- and multi-fraction SRS are lacking long-term local control outcomes and are limited by selection bias as well as single-fraction arms with higher BED, which is correlated with improved local control. Our study will isolate the effect of fractionation by comparing one-year local control in patients treated with single- and multi-fraction SRS with equivalent BED. We anticipate that the results of this, as well as secondary endpoints such as pain response, adverse effects, and quality of life will provide much-needed guidance regarding optimal dose and fractionation for both maximizing local control and minimizing toxicity.

CLINICAL TRIAL INFORMATION

NCT#06173401. Approved by Stanford Scientific Review Committee (study ID: BRN0060) on 9/12/2023 and Stanford Institutional Review Board (study ID: IRB-72248) on 11/14/2023.

Assessment of automated non-coplanar stereotactic radiosurgery planning in single isocenteric linac-based treatment for brain metastases with respect to planner's experience

One of the reasons for planning heterogeneity is lack of enough experience and recommendations on the quality of Linac-based stereotactic radiosurgery (SRS). In this study, our goal is to investigate the impact of planner's experience on the quality of Linac-based SRS plans for brain metastases (BMs) with varying levels of complexity. Specifically, to assess the impact of experience on the outcome of an automated noncoplanar treatment planning. A cohort of 120 patients with intracranial SRS plans, with a total of 633 BMs, was examined using VMAT delivery calculated with an available automated plan delivery system. Four planners with different levels of experience, ranging from under 1 year to over 5 years (Expert planner) of SRS planning, generated treatment plans. Dosimetric parameters and plan quality metrics were evaluated including: conformality index, homogeneity index, modulation factor, R50%, total volume of brain receiving 12Gy, 6Gy, and 3Gy (V12Gy, V6Gy, V3Gy) were assessed for each plan and compared with plan which was created by an expert planner with the highest planning experience. Experienced planners consistently produced acceptable plans, while less experienced one required revisions. Single BM cases showed minimal deviations in dosimetric parameters (under 10%) irrespective of planner experience. However, as the number and complexity of BMs increased, differences in plan quality became more pronounced. Moreover, expert planner's plans consistently outperformed others in terms of organs at risk sparing. This difference was particularly pronounced for cases involving the volume of healthy brain tissue. Our study underscores the critical role of planner's experience in the quality of Linac-based SRS plans using an automated planning. By standardizing and enhancing the planning process, the study aims to improve the quality of care for patients with multiple BMs, contributing to more efficient and effective treatments in the field of SRS.

Effects of EGFR-TKIs combined with intracranial radiotherapy in EGFR-mutant non-small cell lung cancer patients with brain metastases: a retrospective multi-institutional analysis

BACKGROUND

Patients with non-small cell lung cancer (NSCLC) are prone to developing brain metastases (BMs), particularly those with epidermal growth factor receptor (EGFR) mutations. In clinical practice, treatment-naïve EGFR-mutant NSCLC patients with asymptomatic BMs tend to choose EGFR-tyrosine kinase inhibitors (TKIs) as first-line therapy and defer intracranial radiotherapy (RT). However, the effectiveness of upfront intracranial RT remains unclear.

METHODS

This was a retrospective study including 217 patients from two institutions between January 2018 and December 2022. Clinical data of NSCLC patients with BMs who received EGFR-TKIs were collected. The patients were assigned to one of the three groups according to the therapeutic modality used: the upfront TKI + stereotactic radiosurgery (SRS) / fractionated stereotactic radiotherapy (fSRS) group (upfront TKI + SRS/fSRS ), the upfront TKI + whole-brain radiotherapy (WBRT) group (upfront TKI + WBRT) and the upfront TKI group.

RESULTS

As of March 8, 2023, the median follow-up duration was 37.3 months (95% CI, 32.5-42.1). The median overall survival (OS) for the upfront TKI + SRS/fSRS, upfront TKI + WBRT, and upfront TKI groups were 37.8, 20.7, and 24.1 months, respectively (p = 0.015). In subgroup analysis, the upfront TKI + SRS/fSRS group demonstrated longer OS compared to the upfront TKI + WBRT and upfront TKI groups in patients treated with first or second-generation EGFR-TKIs (p = 0.021) and patients with L858R mutation (p = 0.017), whereas no survival benefit was observed in three-generation EGFR-TKIs or 19del subgroup. In the multivariable analysis, metachronous BMs, EGFR L858R mutation and nonclassic EGFR mutation were identified as independent risk factors for OS, while a DS-GPA score of 2.0-4.0 was the only independent protective factor.

CONCLUSIONS

This study demonstrated that upfront addition of SRS/fSRS to EGFR-TKIs was associated with longer OS compared to upfront WBRT or upfront TKI alone in EGFR-mutant NSCLC patients with BMs. This improvement was more significant in patients with L858R mutation and those treated with first or second-generation EGFR-TKIs. Further research with a larger sample size is warranted.

Genomic predictors of radiation response: recent progress towards personalized radiotherapy for brain metastases

Radiotherapy remains a key treatment modality for both primary and metastatic brain tumors. Significant technological advances in precision radiotherapy, such as stereotactic radiosurgery and intensity-modulated radiotherapy, have contributed to improved clinical outcomes. Notably, however, molecular genetics is not yet widely used to inform brain radiotherapy treatment. By comparison, genetic testing now plays a significant role in guiding targeted therapies and immunotherapies, particularly for brain metastases (BM) of lung cancer, breast cancer, and melanoma. Given increasing evidence of the importance of tumor genetics to radiation response, this may represent a currently under-utilized means of enhancing treatment outcomes. In addition, recent studies have shown potentially actionable mutations in BM which are not present in the primary tumor. Overall, this suggests that further investigation into the pathways mediating radiation response variability is warranted. Here, we provide an overview of key mechanisms implicated in BM radiation resistance, including intrinsic and acquired resistance and intratumoral heterogeneity. We then discuss advances in tumor sampling methods, such as a collection of cell-free DNA and RNA, as well as progress in genomic analysis. We further consider how these tools may be applied to provide personalized radiotherapy for BM, including patient stratification, detection of radiotoxicity, and use of radiosensitization agents. In addition, we describe recent developments in preclinical models of BM and consider their relevance to investigating radiation response. Given the increase in clinical trials evaluating the combination of radiotherapy and targeted therapies, as well as the rising incidence of BM, it is essential to develop genomically informed approaches to enhance radiation response.

Assessing tumor volumetric reduction with consideration for setup errors based on mathematical tumor model and microdosimetric kinetic model in single-isocenter VMAT for brain metastases

The volumetric reduction rate (VRR) was evaluated with consideration for six degrees-of-freedom (6DoF) patient setup errors based on a mathematical tumor model in single-isocenter volumetric modulated arc therapy (SI-VMAT) for brain metastases. Simulated gross tumor volumes (GTV) of 1.0 cm and dose distribution were created (27 Gy/3 fractions). The distance between the GTV center and isocenter (d) was set at 0-10 cm. The GTV was translated within 0-1.0 mm (Trans) and rotated within 0-1.0° (Rot) in the three axis directions using affine transformation. The tumor growth volume was calculated using a multicomponent mathematical model (MCTM), and lethal effects of irradiation and repair from damage during irradiation were calculated by a microdosimetric kinetic model (MKM) for non-small cell lung cancer (NSCLC) A549 and NCI-H460 (H460) cells. The VRRs were calculated 5 days after the end of irradiation using the physical dose to the GTV for varying d and 6DoF setup errors. The tolerance value of VRR, the GTV volume reduction rate, was set at 5%, based on the pre-irradiation GTV volume. With the exception of the only one A549 condition where (Trans, Rot) = (1.0 mm, 1.0°) was repeated for 3 fractions, all conditions met all the tolerance VRR values for A549 and H460 cells with varying d from 0 to 10 cm. Evaluation based on the mathematical tumor model suggested that if the 6DoF setup errors at each irradiation could be kept within 1.0 mm and 1.0°, there would be little effect on tumor volume regardless of the distance from the isocenter in SI-VMAT.

Multi-institutional report of trastuzumab deruxtecan and stereotactic radiosurgery for HER2 positive and HER2-low breast cancer brain metastases

Trastuzumab-deruxtecan (T-DXd) has demonstrated intracranial efficacy; however, safety and efficacy data remains limited with stereotactic radiosurgery (SRS). A multi-institutional review was performed with HER2+ or HER2-low metastatic breast cancer treated with T-DXd and SRS for active brain metastases. We identified 215 lesions treated over 48 SRS courses in 34 patients. Median follow up from T-DXd initiation was 13.9 months. The cumulative incidence of symptomatic radiation necrosis at 24 months per lesion was 2.1% and per patient 11%. The 12-month LC was 97%. HER2-low was associated with worse distant intracranial control (DIC) (adjusted HR 2.5, 95% CI 1.1-5.6, p = 0.03) and worse systemic progression free survival (PFS) (HR 4.1, 95% CI 1.6-10.7, p = 0.004). Concurrent SRS and T-DXd has excellent local control, without an increased risk of radiation necrosis. HER2-low disease is associated with worse systemic PFS and DIC with T-DXd compared to HER2+.

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.

Exploratory Evaluation of Personalized Ultrafractionated Stereotactic Adaptive Radiation Therapy (PULSAR) With Central Nervous System-Active Drugs in Brain Metastases Treatment

PURPOSE

Brain metastases (BMs) affect an increasing number of cancer patients and are typically managed with stereotactic radiosurgery (SRS). Our institution advocates the use of Personalized Ultrafractionated Stereotactic Adaptive Radiation Therapy (PULSAR), where radiation is delivered in high-dose pulses at extended intervals allowing for treatment adaptation and easy concurrent systemic therapy integration. We explore the integration of PULSAR with central nervous system (CNS)-active drugs (CNS-aDs).

METHODS AND MATERIALS

This study involved a retrospective evaluation of patients treated with PULSAR using Gamma Knife from 2018 to 2024. We collected demographic, clinical, and specific treatment details, as well as outcomes such as local failure (LF) and toxicity rates. Cumulative incidence analysis for LF and toxicity, considering death a competing risk, and Kaplan-Meier survival analysis for overall survival (OS) were conducted.

RESULTS

Analysis included 109 lesions treated with PULSAR, predominantly in patients with lung and breast cancer. The median follow-up was 1.72. The median OS was not reached. The 1- and 2-year LF rates were 5% and 8.9%, respectively, and 3.4% and 5.5% with concurrent CNS-aDs (cCNS-aDs). BMs >2 cm had LF rates of 9.4% at 2 years. No LFs were observed in BMs >2 cm treated with the combined PULSAR+CNS-aDs approach at 2.5 years. Univariate analysis indicated CNS-aD and radioresponsive histologies were associated with decreased LF rates. The 2-year grade 3+ toxicity rate for PULSAR was 8.7%, with no increase in toxicity with cCNS-aDs.

CONCLUSIONS

The integration of PULSAR with CNS-aDs appears to offer excellent local control for larger BMs with limited toxicity. These promising results merit further prospective investigation to validate the findings and potentially establish new treatment protocols.

Immunotherapy benefits for large brain metastases in non-small cell lung cancer

INTRODUCTION

Non-small cell lung cancer (NSCLC) patients with large brain metastases (BrM) defined as >2 cm in diameter historically face grim prognoses. With immunotherapy emerging as a promising avenue for BrM management and being commonly used in NSCLC, its application in addressing large BrM remains underexplored.

METHODS

This retrospective study conducted across the MedStar Georgetown Cancer Network aimed to assess the efficacy of immunotherapy in non-biomarker driven NSCLC patients with large BrM following initial treatment.

RESULTS

Thirty-six patients were included, all of whom underwent neurosurgery and/or radiation before commencing immunotherapy. The median intracranial progression-free survival (PFS) was 9.2 months and the median overall survival (OS) reached 31 months. Utilizing multivariable Cox penalized regression, the intracranial PFS hazard ratio (HR) was 0.07 (95% confidence interval (CI), 0.02-0.26) for patients who received at least 90 days of immunotherapy compared to those who did not. Each additional 30 days of immunotherapy was associated with an OS HR 0.77 (95% CI, 0.67-0.90).

CONCLUSION

This real-world data highlights the potential of immunotherapy in large BrM NSCLC patients, a population often excluded from clinical trials. This study contributes insights that can inform future treatment approaches, emphasizing the need for further exploration of immunotherapy's role in enhancing outcomes for this challenging patient population.

Advances in the Management of Lung Cancer Brain Metastases

Lung cancer, both non-small cell and small cell, harbors a high propensity for spreading to the central nervous system. Radiation therapy remains the backbone of the management of brain metastases. Recent advances in stereotactic radiosurgery have expanded its indications and ongoing studies seek to elucidate optimal fractionation and coordination with systemic therapies, especially targeted inhibitors with intracranial efficacy. Efforts in whole-brain radiotherapy aim to preserve neurocognition and to investigate the need for prophylactic cranial irradiation. As novel combinatorial strategies are tested and prognostic/predictive biomarkers are identified and tested, the management of brain metastases in lung cancer will become increasingly personalized to optimally balance intracranial efficacy with preserving neurocognitive function and patient values.

Central nervous system metastases in advanced non-small cell lung cancer: A review of the therapeutic landscape

Up to 40% of patients with non-small cell lung cancer (NSCLC) develop central nervous system (CNS) metastases. Current treatments for this subgroup of patients with advanced NSCLC include local therapies (surgery, stereotactic radiosurgery, and, less frequently, whole-brain radiotherapy), targeted therapies for oncogene-addicted NSCLC (small molecules, such as tyrosine kinase inhibitors, and antibody-drug conjugates), and immune checkpoint inhibitors (as monotherapy or combination therapy), with multiple new drugs in development. However, confirming the intracranial activity of these treatments has proven to be challenging, given that most lung cancer clinical trials exclude patients with untreated and/or progressing CNS metastases, or do not include prespecified CNS-related endpoints. Here we review progress in the treatment of patients with CNS metastases originating from NSCLC, examining local treatment options, systemic therapies, and multimodal therapeutic strategies. We also consider challenges regarding assessment of treatment response and provide thoughts around future directions for managing CNS disease in patients with advanced NSCLC.

Effective Personalization of Stereotactic Radiosurgery for Brain Metastases in the Modern Era: Opportunities for Innovation

ABSTRACT

As survival rates improve for patients with metastatic disease, more patients are requiring complex treatment for brain metastases. Stereotactic radiosurgery (SRS) is a conformal radiotherapy technique that allows high ablative dose to be delivered to a specific target and is a standard effective local therapy for the treatment of patients with limited brain metastases. This review highlights the current landscape of SRS treatment in the context of modern therapeutic advances and identifies new research frontiers to personalize SRS and maximize the therapeutic ratio.

Stereotactic Body Radiation Therapy Versus Conventional Radiation Therapy for Painful Spinal Metastases: A Comparative Analysis of Randomized Trials and Practical Considerations

PURPOSE

Recent randomized trials have compared the efficacy and safety of stereotactic body radiation therapy (SBRT) with those of standard conventional external beam radiation therapy (cEBRT) for the treatment of painful spinal metastases. We conducted a composite analysis of these trials in order to inform current practice using pooled outcomes.

METHODS AND MATERIALS

Data from each randomized trial were abstracted from the final publications with biologically effective doses (BEDs) recalculated for SBRT and cEBRT. Primary outcome measures were overall pain response (OR) and complete pain response (CR) rates at 1, 3, and 6 months and rates of vertebral compression fracture. Random effects models were used to estimate primary outcome measures, and meta-regression assessed the effect of BED.

RESULTS

Four prospective randomized clinical trials published between 2018 and 2024 were included, with a total of 686 patients (383 and 303 in the SBRT and cEBRT groups, respectively). Dose and fraction (fx) number ranged from 24 Gy/1 fx to 48.5 Gy/10 fx for the SBRT group (median BED using an α-to-β ratio of 10, 50 Gy) and from 8 Gy/1 fx to 30 Gy/10 fx for the cEBRT group (median BED using an α-to-β ratio of 10, 28 Gy). The 1-, 3-, and 6-month OR rates for SBRT and cEBRT were similar: 53.6%, 52.4%, and 58.8% versus 48.4%, 47.9%, and 43.8%, respectively (p > .05). The 3-month CR rate was significantly higher for SBRT than for cEBRT (31.9% vs 14.8%; risk ratio, 2.26; 95% CI, 1.48-3.45; p < .001), but not the 6-month rate (34.4% vs 16.3%; risk ratio, 1.83; 95% CI, 0.74-4.53; p = .194). Vertebral compression fracture rates were similar at 17.3% and 18.4% for SBRT and cEBRT, respectively. No significant dose-dependent effect was observed with increasing BED for any efficacy or safety outcomes.

CONCLUSIONS

OR rates are similar, but CR rates appear higher with SBRT than with cEBRT, yet no dose-dependent effects were identified despite approximately 1.8 × BED dose with SBRT.

Diagnosis and management of brain radiation necrosis

Brain radiation necrosis (BRN) is a significant and complex side effect of stereotactic radiotherapy (SRT). Differentiating BRN from local tumor recurrence is critical, requiring advanced diagnostic techniques and a multidisciplinary approach. BRN typically manifests months to years post-treatment, presenting with radiological changes on MRI and may produce neurological symptoms. Key risk factors include the volume of irradiated brain tissue, the radiation dose, and prior radiotherapy history. This manuscript reviews the diagnostic process for BRN, emphasizing the importance of assessing baseline risk, clinical evaluation, and advanced imaging modalities. Multimodal imaging enhances diagnostic accuracy and aids in distinguishing BRN from tumor relapse. Therapeutic management varies based on symptoms. Asymptomatic BRN may be monitored with regular imaging, while symptomatic BRN often requires corticosteroids to reduce inflammation. Emerging therapies like bevacizumab have shown promise in clinical trials, with significant radiographic and symptomatic improvement. Surgical intervention may be necessary for histological confirmation and severe, treatment-resistant cases. Ongoing research aims to improve diagnostic accuracy and treatment efficacy, enhancing patient outcomes and quality of life. This review underscores the need for a multidisciplinary approach and continuous advancements to address the challenges posed by BRN in brain tumor patients.

Multiomics-Based Outcome Prediction in Personalized Ultra-Fractionated Stereotactic Adaptive Radiotherapy (PULSAR)

Objectives: This retrospective study aims to develop a multiomics approach that integrates radiomics, dosiomics, and delta features to predict treatment responses in brain metastasis (BM) patients undergoing PULSAR. Methods: A retrospective study encompassing 39 BM patients with 69 lesions treated with PULSAR was undertaken. Radiomics, dosiomics, and delta features were extracted from both pre-treatment and intra-treatment MRI scans alongside dose distributions. Six individual models, alongside an ensemble feature selection (EFS) model, were evaluated. The classification task focused on distinguishing between two lesion groups based on whether they exhibited a volume reduction of more than 20% at follow-up. Performance metrics, including sensitivity, specificity, accuracy, precision, F1 score, and the area under the receiver operating characteristic (ROC) curve (AUC), were assessed. Results: The EFS model integrated the features from pre-treatment radiomics, pre-treatment dosiomics, intra-treatment radiomics, and delta radiomics. It outperformed six individual models, achieving an AUC of 0.979, accuracy of 0.917, and F1 score of 0.821. Among the top nine features of the EFS model, six features came from post-wavelet transformation and three from original images. Conclusions: The study demonstrated the feasibility of employing a data-driven multiomics approach to predict treatment outcomes in BM patients receiving PULSAR treatment. Integrating multiomics with intra-treatment decision support in PULSAR shows promise for optimizing patient management and reducing the risks of under- or over-treatment.

Digital "flipbooks" for enhanced visual assessment of simple and complex brain tumors

Typical longitudinal radiographic assessment of brain tumors relies on side-by-side qualitative visualization of serial magnetic resonance images (MRIs) aided by quantitative measurements of tumor size. However, when assessing slowly growing tumors and/or complex tumors, side-by-side visualization and quantification may be difficult or unreliable. Whole-brain, patient-specific "digital flipbooks" of longitudinal scans are a potential method to augment radiographic side-by-side reads in clinical settings by enhancing the visual perception of changes in tumor size, mass effect, and infiltration across multiple slices over time. In this approach, co-registered, consecutive MRI scans are displayed in a slide deck, where one slide displays multiple brain slices of a single timepoint in an array (eg, 3 × 5 "mosaic" view of slices). The flipbooks are viewed similarly to an animated flipbook of cartoons/photos so that subtle radiographic changes are visualized via perceived motion when scrolling through the slides. Importantly, flipbooks can be created easily with free, open-source software. This article describes the step-by-step methodology for creating flipbooks and discusses clinical scenarios for which flipbooks are particularly useful. Example flipbooks are provided in Supplementary Material.

Lazertinib in EGFR-Variant Non-Small Cell Lung Cancer With CNS Failure to Prior EGFR Tyrosine Kinase Inhibitors: A Nonrandomized Controlled Trial

Importance

EGFR-variant non-small cell lung cancer (NSCLC) is associated with a high rate of central nervous system (CNS) metastases, even with treatment with first-generation or second-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs).

Objective

To investigate CNS activity with lazertinib, a third-generation EGFR TKI.

Design, Setting, and Participants

This multicenter single-arm, phase 2 nonrandomized controlled trial was conducted in South Korea and included patients with EGFR-variant NSCLC who had asymptomatic or mildly symptomatic brain metastases after unsuccessful treatment with first-generation or second-generation EGFR TKIs. Data were collected from June 2021 to April 2022, with a data cutoff date of December 15, 2022.

Exposure

Lazertinib, 240 mg, once daily.

Main Outcomes and Measures

The primary end point was intracranial objective response rate (iORR) in the evaluable population according to the Response Evaluation Criteria in Solid Tumours version 1.1 assessed by the investigators. Secondary end points included intracranial progression-free survival (iPFS) and iORR in patients with T790M-negative disease and isolated CNS progression as well as overall ORR, duration of response, intracranial duration of response, disease control rate, overall survival, cerebrospinal fluid penetration of lazertinib, and safety.

Results

Among 40 included patients, 25 (63%) were women, and the median (range) age was 63 (29-85) years. A total of 38 patients were evaluable for tumor response, including 12 patients with leptomeningeal metastases. At data cutoff, the median (range) follow-up was 13.6 (2.9-17.7) months. The iORR for the evaluable population was 55% (21 of 38; 95% CI, 38.3-71.4); for patients with T790M-positive disease, 80% (4 of 5; 95% CI, 28.4-99.5); for patients with T790M-negative disease, 43% (9 of 21; 95% CI, 21.8-66.0); and for patients with T790M-unknown disease, 67% (8 of 12; 95% CI, 34.9-90.1). The median iPFS was 15.8 months (95% CI, 15.2-not reached) for the evaluable population, 15.2 months (95% CI, 4.2-not reached) for the T790M-positive subgroup, 15.4 months (95% CI, 7.9-not reached) for the T790M-negative subgroup, and 18.0 months (95% CI, 3.9-not reached) for the T790M-unknown subgroup. The cerebrospinal fluid penetration rate of lazertinib was 46.2% (95% CI, 10.0-49.6), providing further support for its mechanism of intracranial response. Most adverse events were grade 1 or 2.

Conclusions and Relevance

In this study, lazertinib had substantial CNS activity, regardless of T790M status, against the progression of intracranial metastases with or without leptomeningeal metastases after unsuccessful treatment with first-generation or second-generation EGFR TKIs in patients with metastatic EGFR-variant NSCLC. These results suggest that using lazertinib instead of brain local treatment could be a potential strategy in patients with EGFR-variant NSCLC whose CNS metastases progressed after prior EGFR TKI treatment.

Trial Registration

ClinicalTrials.gov Identifier: NCT05326425.

Determinants of cerebral radionecrosis in animal models: A systematic review

BACKGROUND

Radionecrosis is a common complication in radiation oncology, while mechanisms and risk factors have yet to be fully explored. We therefore conducted a systematic review to understand the pathogenesis and identify factors that significantly affect the development.

METHODS

We performed a systematic literature search based on the PRISMA guidelines using PubMed, Ovid, and Web of Science databases. The complete search strategy can be found as a preregistered protocol on PROSPERO (CRD42023361662).

RESULTS

We included 83 studies, most involving healthy animals (n = 72, 86.75 %). High doses of hemispherical irradiation of 30 Gy in rats and 50 Gy in mice led repeatedly to radionecrosis among different studies and set-ups. Higher dose and larger irradiated volume were associated with earlier onset. Fractionated schedules showed limited effectiveness in the prevention of radionecrosis. Distinct anatomical brain structures respond to irradiation in various ways. White matter appears to be more vulnerable than gray matter. Younger age, more evolved animal species, and genetic background were also significant factors, whereas sex was irrelevant. Only 13.25 % of the studies were performed on primary brain tumor bearing animals, no studies on brain metastases are currently available.

CONCLUSION

This systematic review identified various factors that significantly affect the induction of radionecrosis. The current state of research neglects the utilization of animal models of brain tumors, even though patients with brain malignancies constitute the largest group receiving brain irradiation. This latter aspect should be primarily addressed when developing an experimental radionecrosis model for translational implementation.

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.

Multifraction stereotactic radiotherapy utilizing inhomogeneous dose distribution for brainstem metastases: a single-center retrospective analysis

Brainstem metastases are challenging to manage owing to the critical neurological structures involved. Although stereotactic radiotherapy (SRT) offers targeted high doses while minimizing damage to adjacent normal tissues, the optimal dose fractionation remains undefined. This study evaluated the efficacy and safety of multifraction SRT with an inhomogeneous dose distribution. This retrospective study included 31 patients who underwent 33 treatments for 35 brainstem lesions using linear accelerator-based multifraction SRT (30 Gy in five fractions, 35 Gy in five fractions or 42 Gy in 10 fractions) with an inhomogeneous dose distribution (median isodose, 51.9%). The outcomes of interest were local failure, toxicity and symptomatic failure. The median follow-up time after brainstem SRT for a lesion was 18.6 months (interquartile range, 10.0-24.3 months; range, 1.8-39.0 months). Grade 2 toxicities were observed in two lesions, and local failure occurred in three lesions. No grade 3 or higher toxicities were observed. The 1-year local and symptomatic failure rates were 8.8 and 16.7%, respectively. Toxicity was observed in two of seven treatments with a gross tumor volume (GTV) greater than 1 cc, whereas no toxicity was observed in treatments with a GTV less than 1 cc. No clear association was observed between the biologically effective dose of the maximum brainstem dose and the occurrence of toxicity. Our findings indicate that multifraction SRT with an inhomogeneous dose distribution offers a favorable balance between local control and toxicity in brainstem metastases. Larger multicenter studies are needed to validate these results and determine the optimal dose fractionation.

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.

Are Dual-Phase 18F-Fluorodeoxyglucose PET-mpMRI Diagnostic Performances to Distinguish Brain Tumour Radionecrosis/Recurrence after Cranial Radiotherapy Usable in Routine?

Brain metastases or primary brain tumours had poor prognosis until the use of high dose radiotherapy. However, radionecrosis is a complex challenge in the post-radiotherapy management of these patients due to the difficulty of distinguishing this complication from local tumour recurrence. MRI alone has a variable specificity and sensibility, as does PET-CT imaging. We aimed to investigate the diagnostic performance of dual-phase 18F-FDG PET-mpMRI to distinguish cerebral radionecrosis from local tumour recurrence after cranial radiotherapy. A retrospective analysis was conducted between May 2021 and September 2022. Inclusion criteria encompassed patients with inconclusive MRI findings post-radiotherapy and history of cerebral radiotherapy for primary or metastatic brain lesions. Lesions are assessed qualitatively and semi-quantitatively. The gold standard to assess radionecrosis was histopathology or a composite criterion at three months. The study evaluated 24 lesions in 23 patients. Qualitative analysis yielded 85.7% sensitivity and 75% specificity. Semi-quantitative analysis, based on contralateral background noise, achieved 100% sensitivity and 50% specificity. Moreover, using contralateral frontal lobe background noise resulted in higher performances with 92% sensitivity and 63% specificity. Stratification by lesion type demonstrated 100% sensitivity and specificity rates for metastatic lesions. The diagnostic performance of dual-phase 18F-FDG PET-mpMRI shows promising results for metastatic lesions.

Phase I trial of dose escalation for preoperative stereotactic radiosurgery for patients with large brain metastases

BACKGROUND

Single-session stereotactic radiosurgery (SRS) or surgical resection alone for brain metastases larger than 2 cm results in unsatisfactory local control. We conducted a phase I trial for brain metastases(>2 cm) to determine the safety of preoperative SRS at escalating doses.

METHODS

Radiosurgery dose was escalated at 3 Gy increments for 3 cohorts based on maximum tumor dimension starting at: 18 Gy for >2-3 cm, 15 Gy for >3-4 cm, and 12 Gy for >4-6 cm. Dose-limiting toxicity was defined as grade III or greater acute toxicity.

RESULTS

A total of 35 patients/36 lesions were enrolled. For tumor size >2-3 cm, patients were enrolled up to the second dose level (21 Gy); for >3-4 cm and >4-6 cm cohorts the third dose level (21 and 18 Gy, respectively) was reached. There were 2 DLTs in the >3-4 cm arm at 21 Gy. The maximum tolerated dose of SRS for >2-3 cm was not reached; and was 18 Gy for both >3-4 cm arm and >4-6 cm arm. With a median follow-up of 64.0 months, the 6- and 12-month local control rates were 85.9% and 76.6%, respectively. One patient developed grade 3 radiation necrosis at 5 months. The 2-year rate of leptomeningeal disease (LMD) was 0%.

CONCLUSIONS

Preoperative SRS with dose escalation followed by surgical resection for brain metastases greater than 2 cm in size demonstrates acceptable acute toxicity. The phase II portion of the trial will be conducted at the maximum tolerated SRS doses.

Exploring feasibility criteria for stereotactic radiosurgical treatment of multiple brain metastases using five linac machines

PURPOSE

This study aimed to find descriptors that correlates with normal brain dose to determine the feasibility of performing fractionated stereotactic radiosurgery (SRS) for multiple brain metastases (BMs) using five linac machines.

METHODS

Thirty-two patients with 1-30 BMs were enrolled. Treatment plans were created using TrueBeam, Novalis Tx, TrueBeam Edge, Halcyon, and Tomotherapy linacs. The sum of all planning target volumes (PTVs) was defined as PTVall, and the brain region excluding PTVall was defined as normal brain. The total surface area (TSA) of the PTV was calculated from the sum of the surface areas of the equivalent spheres for each PTV. Volumes receiving more than 5, 12, and 18 Gy (V5Gy, V12Gy, and V18Gy, respectively) were used for evaluation of normal brain dose. Correlations between normal brain dose and each tumor characteristic (number, PTVall, and TSA) were investigated using the Spearman rank correlation coefficient.

RESULTS

Correlations between each characteristic and normal brain dose were statistically significant (p < 0.05) across all machines. The correlation coefficients between each characteristic and V18Gy for the five machines were as follows: tumor number, 0.39-0.60; PTVall, 0.79-0.93; TSA, 0.93-0.99. The fit equations between TSA and V18Gy exhibited high coefficients of determination, ranging from 0.92 to 0.99 across five machines.

CONCLUSION

This study devised fractionated SRS plans using for 1-30 BMs across five linac machines to find descriptors for determining SRS feasibility based on normal brain dose. TSA proved to be a promising descriptor of SRS feasibility for treating multiple BMs.

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.

Frameless stereotactic radiosurgery for brain metastasis: a systematic review and meta-analysis

Stereotactic Radiosurgery (SRS) delivers a high dose of radiation to a specific brain area while limiting radiation to nearby healthy tissue. While most SRS has traditionally been performed with a stereotactic frame-based approach, this study aims to investigate the safety and efficacy of frameless radiosurgery in patients with brain metastases. Our study followed the recommended guidelines summarized in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist. The electronic databases of PubMed/Medline, Scopus, Embase, and Web of Science (WOS) were searched from inception to 10 October 2023. The pooled rate of outcomes was calculated using random effect model and Restricted maximum-likelihood (REML) method. All statistical analysis was performed by STATA V.17. A total of 499 studies were recruited from the electronic databases. After removing duplicates (n = 117), 382 studies were used for title/abstract, and 329 were removed from the study selection process. A total of 53 articles were used for full-text assessment, and 35 studies were included for data extraction. Our analysis revealed a significant increase across all pooled survival rates and local control rates by initiating the radiosurgery for patients, estimating the pooled 6-month OSR of 75% (95% CI: 68-81%), 1-year overall survival rate (OSR) of 60% (95% CI: 51-69%), 18-month OSR of 48% (95% CI: 10-85%), 2-year OSR of 39% (95% CI: 19-58%), 1-year progression-free survival rate (PFSR) of 68% (95% CI: 39-98%), 2-year PFSR of 75% (95% CI: 58-91%), 6-month local control rate (LCR) of 93% (95% CI: 90-96%), and 12-month LCR of 86% (95% CI: 82-90%). Our meta-analysis findings confirm the efficacy of frameless radiosurgery in treating brain metastases. Using data from several trials, we were able to demonstrate stereotactic radiosurgery's effectiveness as a therapy option for brain metastasis patients, demonstrating local control and reasonable overall survival.

Single versus multiple fraction stereotactic radiosurgery for medium-sized brain metastases (4-14 cc in volume): reducing or fractionating the radiosurgery dose?

Background and purpose

Stereotactic radiosurgery (SRS) of brain metastases (BM) and resection cavities is a widely used and effective treatment modality. Based on target lesion size and anatomical location, single fraction SRS (SF-SRS) or multiple fraction SRS (MF-SRS) are applied. Current clinical recommendations conditionally recommend either reduced dose SF-SRS or MF-SRS for medium-sized BM (2-2.9 cm in diameter). Despite excellent local control rates, SRS carries the risk of radionecrosis (RN). The purpose of this study was to assess the 12-months local control (LC) rate and 12-months RN rate of this specific patient population.

Materials and methods

This single-center retrospective study included 54 patients with medium-sized intact BM (n=28) or resection cavities (n=30) treated with either SF-SRS or MF-SRS. Follow-up MRI was used to determine LC and RN using a modification of the "Brain Tumor Reporting and Data System" (BT-RADS) scoring system.

Results

The 12-month LC rate following treatment of intact BM was 66.7% for SF-SRS and 60.0% for MF-SRS (p=1.000). For resection cavities, the 12-month LC rate was 92.9%% after SF-SRS and 46.2% after MF-SRS (p=0.013). For intact BM, RN rate was 17.6% for SF-SRS and 20.0% for MF-SRS (p=1.000). For resection cavities, RN rate was 28.6% for SF-SRS and 20.0% for MF-SRS (p=1.000).

Conclusion

Patients with intact BM showed no statistically significant differences in 12-months LC and RN rate following SF-SRS or MF-SRS. In patients with resection cavities the 12-months LC rate was significantly better following SF-SRS, with no increase in the RNFS.

Recent advances in breast cancer metastasis with special emphasis on metastasis to the brain

Understanding the underlying mechanisms of breast cancer metastasis is of vital importance for developing treatment approaches. This review emphasizes contemporary breakthrough studies with special focus on breast cancer brain metastasis. Acquired mutational changes in metastatic lesions are often distinct from the primary tumor, suggesting altered mutagenesis pathways. The concept of micrometastases and heterogeneity within the tumors unravels novel therapeutic targets at genomic and molecular levels through epigenetic and proteomic profiling. Several pre-clinical studies have identified mechanisms involving the immune system, where tumor associated macrophages are key players. Expression of cell proteins like Syndecan1, fatty acid-binding protein 7 and tropomyosin kinase receptor B have been implicated in aiding the transmigration of breast cancer cells to the brain. Changes in the proteomic landscape of the blood-brain-barrier show altered permeability characteristics, supporting entry of cancer cells. Findings from laboratory studies pave the path for the emergence of new biomarkers, especially blood-based miRNA and circulating tumor cell markers for prognostic staging. The constantly evolving therapeutics call for clinical trials backing supportive evidence of efficacies of both novel and existing approaches. The challenge lying ahead is discovering innovative techniques to replace use of human samples and optimize small-scale patient recruitment in trials.

Hypofractionated Stereotactic Radiosurgery in the Management of Brain Metastases

Stereotactic radiosurgery (SRS) is an important weapon in the management of brain metastases. Single-fraction SRS is associated with local control rates ranging from approximately 70% to 100%, which are largely dependent on lesion and postoperative cavity size. The rates of local control and improved neurocognitive outcomes compared with conventional whole-brain radiation therapy have led to increased adoption of SRS in these settings. However, when treating larger targets and/or targets located in eloquent locations, the risk of normal tissue toxicity and adverse radiation effects within healthy brain tissue becomes significantly higher. Thus, hypofractionated SRS has become a widely adopted approach, which allows for the delivery of ablative doses of radiation while also minimizing the risk of toxicity. This approach has been studied in multiple retrospective reports in both the postoperative and intact settings. While there are no reported randomized data to date, there are trials underway evaluating this paradigm. In this article, we review the role of hypofractionated SRS in the management of brain metastases and emerging data that will serve to validate this treatment approach. Pertinent articles and references were obtained from a comprehensive search of PubMed/MEDLINE and clinicaltrials.gov .

Comparative evaluation of outcomes amongst different radiosurgery management paradigms for patients with large brain metastasis

INTRODUCTION

This study compares four management paradigms for large brain metastasis (LMB): fractionated SRS (FSRS), staged SRS (SSRS), resection and postoperative-FSRS (postop-FSRS) or preoperative-SRS (preop-SRS).

METHODS

Patients with LBM (≥ 2 cm) between July 2017 and January 2022 at a single tertiary institution were evaluated. Primary endpoints were local failure (LF), radiation necrosis (RN), leptomeningeal disease (LMD), a composite of these variables, and distant intracranial failure (DIF). Gray's test compared cumulative incidence, treating death as a competing risk with a random survival forests (RSF) machine-learning model also used to evaluate the data.

RESULTS

183 patients were treated to 234 LBMs: 31.6% for postop-FSRS, 28.2% for SSRS, 20.1% for FSRS, and 20.1% for preop-SRS. The overall 1-year composite endpoint rates were comparable (21 vs 20%) between nonoperative and operative strategies, but 1-year RN rate was 8 vs 4% (p = 0.012), 1-year overall survival (OS) was 48 vs. 69% (p = 0.001), and 1-year LMD rate was 5 vs 10% (p = 0.052). There were differences in the 1-year RN rates (7% FSRS, 3% postop-FSRS, 5% preop-SRS, 10% SSRS, p = 0.037). With RSF analysis, the out-of-bag error rate for the composite endpoint was 47%, with identified top-risk factors including widespread extracranial disease, > 5 total lesions, and breast cancer histology.

CONCLUSION

This is the first study to conduct a head-to-head retrospective comparison of four SRS methods, addressing the lack of randomized data in LBM literature amongst treatment paradigms. Despite patient characteristic trends, no significant differences were found in LF, composite endpoint, and DIF rates between non-operative and operative approaches.

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.

Brain Metastasis in the Emergency Department: Epidemiology, Presentation, Investigations, and Management

Brain metastases (BMs) are the most prevalent type of cerebral tumor, significantly affecting survival. In adults, lung cancer, breast cancer, and melanoma are the primary cancers associated with BMs. Symptoms often result from brain compression, and patients may present to the emergency department (ED) with life-threatening conditions. The goal of treatment of BMs is to maximize survival and quality of life by choosing the least toxic therapy. Surgical resection followed by cavity radiation or definitive stereotactic radiosurgery remains the standard approach, depending on the patient's condition. Conversely, whole brain radiation therapy is becoming more limited to cases with multiple inoperable BMs and is less frequently used for postoperative control. BMs often signal advanced systemic disease, and patients usually present to the ED with poorly controlled symptoms, justifying hospitalization. Over half of patients with BMs in the ED are admitted, making effective ED-based management a challenge. This article reviews the epidemiology, clinical manifestations, and current treatment options of patients with BMs. Additionally, it provides an overview of ED management and highlights the challenges faced in this setting. An improved understanding of the reasons for potentially avoidable hospitalizations in cancer patients with BMs is needed and could help emergency physicians distinguish patients who can be safely discharged from those who require observation or hospitalization.

Lexicographic optimization-based planning for stereotactic radiosurgery of brain metastases

AIM

To validate a fully-automated lexicographic optimization-planning system (mCycle, Elekta) for single-(SL) and multiple-(ML, up to 4 metastases) lesions in intracranial stereotactic radiosurgery (SRS, 21 Gy, single fraction).

METHODS

A pre-determined priority list, Wish-List (WL), represents a dialogue between planner and clinician, establishing strict constraints and pursuing objectives. In order to satisfy the clinical protocol without manual intervention, four patients were required to tweak and fine-tune each WL (SLp, MLp) for coplanar arcs. Thirty-five testing plans (20 SLp, 15 MLp) were automatically re-planned (mCP). Automatic and manual plans were compared including dose constraints, conformality, modulation complexity score (MCS), delivery time, and local gamma analysis (2%/2 mm). To ensure plan clinical acceptability, two radiation oncologists conducted an independent blind plan choice.

RESULTS

Each WL-tuning took 3 days. Estimated median manual plans and mCP calculation time were 8 and 3 h, respectively. Significant increases in SLp and MLp target coverage and conformity were registered. mCP showed a not significant and clinically acceptable higher median brain V12Gy. SLp registered a -5.8% MU decrease with comparable median delivery time (MP 2.0 min, mCP 1.9 min) while MLp showed a +9.8% MU increase and longer delivery time (MP 3.5 min, mCP 4.4 min). mCP MCS resulted significantly higher without affecting gamma passing rates. At blind choice, mCP were preferred in the majority of cases.

CONCLUSIONS

Lexicographic optimization produced acceptable SRS plans with coplanar arcs significantly reducing the overall planning time in cases with up to 4 brain metastases. These planning improvements suggest further investigations by setting high-quality non-coplanar arc plans as a reference.

Factors associated with the local control of brain metastases: a systematic search and machine learning application

BACKGROUND

Enhancing Local Control (LC) of brain metastases is pivotal for improving overall survival, which makes the prediction of local treatment failure a crucial aspect of treatment planning. Understanding the factors that influence LC of brain metastases is imperative for optimizing treatment strategies and subsequently extending overall survival. Machine learning algorithms may help to identify factors that predict outcomes.

METHODS

This paper systematically reviews these factors associated with LC to select candidate predictor features for a practical application of predictive modeling. A systematic literature search was conducted to identify studies in which the LC of brain metastases is assessed for adult patients. EMBASE, PubMed, Web-of-Science, and the Cochrane Database were searched up to December 24, 2020. All studies investigating the LC of brain metastases as one of the endpoints were included, regardless of primary tumor type or treatment type. We first grouped studies based on primary tumor types resulting in lung, breast, and melanoma groups. Studies that did not focus on a specific primary cancer type were grouped based on treatment types resulting in surgery, SRT, and whole-brain radiotherapy groups. For each group, significant factors associated with LC were identified and discussed. As a second project, we assessed the practical importance of selected features in predicting LC after Stereotactic Radiotherapy (SRT) with a Random Forest machine learning model. Accuracy and Area Under the Curve (AUC) of the Random Forest model, trained with the list of factors that were found to be associated with LC for the SRT treatment group, were reported.

RESULTS

The systematic literature search identified 6270 unique records. After screening titles and abstracts, 410 full texts were considered, and ultimately 159 studies were included for review. Most of the studies focused on the LC of the brain metastases for a specific primary tumor type or after a specific treatment type. Higher SRT radiation dose was found to be associated with better LC in lung cancer, breast cancer, and melanoma groups. Also, a higher dose was associated with better LC in the SRT group, while higher tumor volume was associated with worse LC in this group. The Random Forest model predicted the LC of brain metastases with an accuracy of 80% and an AUC of 0.84.

CONCLUSION

This paper thoroughly examines factors associated with LC in brain metastases and highlights the translational value of our findings for selecting variables to predict LC in a sample of patients who underwent SRT. The prediction model holds great promise for clinicians, offering a valuable tool to predict personalized treatment outcomes and foresee the impact of changes in treatment characteristics such as radiation dose.

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.

Case report: Long-term intracranial effect of zimberelimab monotherapy following surgical resection of high PD-L1-expressing brain metastases from NSCLC

Non-small cell lung cancer (NSCLC) accounted for the majority of lung cancer cases worldwide. Brain metastases (BM) frequently complicate NSCLC and portend a dismal prognosis. To control neurological symptoms, surgical resection is commonly followed by brain radiotherapy (RT). However, RT is often complicated by neurotoxicity. For patients with tumors that harbor positive driver genes, tyrosine kinase inhibitors are considered the standard of care. Nevertheless, treatment options for those without driver gene mutations are still debated. Programmed death receptor 1 (PD-1)/ligand 1 (PD-L1) inhibition has emerged as a novel therapeutic strategy for NSCLC patients with PD-L1-positive tumors, as well as for those with asymptomatic BM. However, the effect of anti-PD-1 antibodies on active BM within such specific populations is undetermined. Herein we present a case of a 65-year-old patient with NSCLC and high PD-L1-expressing BM. The patient underwent surgical resection of BM followed by first-line monotherapy with 31 cycles of zimberelimab, a novel anti-PD-1 antibody, and has already achieved 24 months of progression-free survival and intracranial recurrence-free survival. To our knowledge, this is the first report regarding the intracranial effect of zimberelimab on BM from primary lung cancer. This case report might facilitate an understanding of the intracranial effects of different anti-PD-1 antibodies for such populations.

Response of treatment-naive brain metastases to stereotactic radiosurgery

With improvements in survival for patients with metastatic cancer, long-term local control of brain metastases has become an increasingly important clinical priority. While consensus guidelines recommend surgery followed by stereotactic radiosurgery (SRS) for lesions >3 cm, smaller lesions (≤3 cm) treated with SRS alone elicit variable responses. To determine factors influencing this variable response to SRS, we analyzed outcomes of brain metastases ≤3 cm diameter in patients with no prior systemic therapy treated with frame-based single-fraction SRS. Following SRS, 259 out of 1733 (15%) treated lesions demonstrated MRI findings concerning for local treatment failure (LTF), of which 202 /1733 (12%) demonstrated LTF and 54/1733 (3%) had an adverse radiation effect. Multivariate analysis demonstrated tumor size (>1.5 cm) and melanoma histology were associated with higher LTF rates. Our results demonstrate that brain metastases ≤3 cm are not uniformly responsive to SRS and suggest that prospective studies to evaluate the effect of SRS alone or in combination with surgery on brain metastases ≤3 cm matched by tumor size and histology are warranted. These studies will help establish multi-disciplinary treatment guidelines that improve local control while minimizing radiation necrosis during treatment of brain metastasis ≤3 cm.

Prediction of the treatment response and local failure of patients with brain metastasis treated with stereotactic radiosurgery using machine learning: A systematic review and meta-analysis

BACKGROUND

Stereotactic radiosurgery (SRS) effectively treats brain metastases. It can provide local control, symptom relief, and improved survival rates, but it poses challenges in selecting optimal candidates, determining dose and fractionation, monitoring for toxicity, and integrating with other modalities. Practical tools to predict patient outcomes are also needed. Machine learning (ML) is currently used to predict treatment outcomes. We aim to investigate the accuracy of ML in predicting treatment response and local failure of brain metastasis treated with SRS.

METHODS

PubMed, Scopus, Web of Science (WoS), and Embase were searched until April 16th, which was repeated on October 17th, 2023 to find possible relevant papers. The study preparation adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. The statistical analysis was performed by the MIDAS package of STATA v.17.

RESULTS

A total of 17 articles were reviewed, of which seven and eleven were related to the clinical use of ML in predicting local failure and treatment response. The ML algorithms showed sensitivity and specificity of 0.89 (95% CI: 0.84-0.93) and 0.87 (95% CI: 0.81-0.92) for predicting treatment response. The positive likelihood ratio was 7.1 (95% CI: 4.5-11.1), the negative likelihood ratio was 0.13 (95% CI: 0.08-0.19), and the diagnostic odds ratio was 56 (95% CI: 25-125). Moreover, the pooled estimates for sensitivity and specificity of ML algorithms for predicting local failure were 0.93 (95% CI: 0.76-0.98) and 0.80 (95% CI: 0.53-0.94). The positive likelihood ratio was 4.7 (95% CI: 1.6-14.0), the negative likelihood ratio was 0.09 (95% CI: 0.02-0.39), and the diagnostic odds ratio was 53 (95% CI: 5-606).

CONCLUSION

ML holds promise in predicting treatment response and local failure in brain metastasis patients receiving SRS. However, further studies and improvements in the treatment process can refine the models and effectively integrate them into clinical practice.

Multicentric Assessment of Safety and Efficacy of Combinatorial Adjuvant Brain Metastasis Treatment by Intraoperative Radiation Therapy and Immunotherapy

PURPOSE

After surgical resection of brain metastases (BMs), intraoperative radiation therapy (IORT) provides a promising alternative to adjuvant external beam radiation therapy by enabling superior organ-at-risk preservation, reduction of in-hospital times, and timely admission to subsequent systemic treatments, which increasingly comprise novel targeted immunotherapeutic approaches. We sought to assess the safety and efficacy of IORT in combination with immune checkpoint inhibitors (ICIs) and other targeted therapies (TTs).

METHODS AND MATERIALS

In a multicentric approach incorporating individual patient data from 6 international IORT centers, all patients with BMs undergoing IORT were retrospectively assessed for combinatorial treatment with ICIs/TTs and evaluated for toxicity and cumulative rates, including wound dehiscence, radiation necrosis, leptomeningeal spread, local control, distant brain progression (DBP), and estimated overall survival.

RESULTS

In total, 103 lesions with a median diameter of 34 mm receiving IORT combined with immunomodulatory systemic treatment or other TTs were included. The median follow-up was 13.2 (range, 1.2-102.4) months, and the median IORT dose was 25 (range, 18-30) Gy prescribed to the applicator surface. There was 1 grade 3 adverse event related to IORT recorded (2.2%). A 4.9% cumulative radiation necrosis rate was observed. The 1-year local control rate was 98.0%, and the 1-year DBP-free survival rate was 60.0%. Median time to DBP was 5.5 (range, 1.0-18.5) months in the subgroup of patients experiencing DBP, and the cumulative leptomeningeal spread rate was 4.9%. The median estimated overall survival was 26 (range, 1.2 to not reached) months with a 1-year survival rate of 74.0%. Early initiation of immunotherapy/TTs was associated with a nonsignificant trend toward improved DBP rate and overall survival.

CONCLUSIONS

The combination of ICIs/TTs with IORT for resected BMs does not seem to increase toxicity and yields encouraging local control outcomes in the difficult-to-treat subgroup of larger BMs. Time gaps between surgery and systemic treatment could be shortened or avoided. The definitive role of IORT in local control after BM resection will be defined in a prospective trial.

Symptomatic brain metastases in melanoma

Although clinical outcomes in metastatic melanoma have improved in recent years, the morbidity and mortality of symptomatic brain metastases remain challenging. Response rates and survival outcomes of patients with symptomatic melanoma brain metastases (MBM) are significantly inferior to patients with asymptomatic disease. This review focusses upon the specific challenges associated with the management of symptomatic MBM, discussing current treatment paradigms, obstacles to improving clinical outcomes and directions for future research.