UK 2022 Consensus on Normal Tissue Dose-Volume Constraints for Oligometastatic, Primary Lung and Hepatocellular Carcinoma Stereotactic Ablative Radiotherapy

Dosimetric investigation of multi-parametric 4D-MRI for radiotherapy in liver cancer

BACKGROUND

In radiotherapy, inadequate management of organ motion in liver cancer may lead to inadequate delineation accuracy, resulting in the underdosage of target tissues and overdosage of surrounding normal tissues. To investigate the clinical potential of multi-parametric 4D-MRI in the target delineation and dose accuracy for liver cancer radiotherapy.

METHODS

Twenty patients receiving radiotherapy for liver cancer were enrolled. Each patient underwent contrast-enhanced planning CT (free-breathing), contrast-enhanced T1-weighted (free-breathing), T2-weighted (gated) 3D-MRI, and low-quality 4D-MRI using the time resolved imaging with interleaved stochastic trajectories volumetric interpolated breath-hold examination (TWIST-VIBE) sequence. A dual-supervised deformation estimation model was used to generate a 4D deformable vector field (4D-DVF) from 4D-MRI data, and the prior images were deformed using this 4D-DVF to generate multi-parametric 4D-MRI. Assisted by 3D-MRI and multi-parametric 4D-MRI, target contours were performed on the planning CT, resulting in the generation of Target_3D and Target_4D. Clinical plans, Plan_3D and Plan_4D, were designed based on these contours respectively. To explore the dosimetric variations resulting from different contours without re-optimization, Plan_3D was directly applied to Target_4D, and Plan_4D was applied to Target_3D to generate Plan_3D' and Plan_4D' respectively. Target volume, contours, dose-volume histograms (DVHs), conformity index (CI), homogeneity index (HI), maximum and mean dose to organ as risks (OARs) were compared and evaluated.

RESULTS

Mean volume differences between Target_3D and Target_4D were 2.76 cm3 (standard deviation [SD] 3.42 cm3) in the caudate lobe, 181.54 cm3 (SD 68.50 cm3) in the left hepatic lobe, and 26.08 cm3 (SD 20.52 cm3) in the right hepatic lobe. Mean and SD of CI and HI is 1.02 ± 0.04 and 0.108 ± 0.02 in Plan_3D, 1.02 ± 0.01 and 0.107 ± 0.01 in Plan_4D. There were no statistically significant differences in OAR doses between Plan_3D and Plan_3D', between Plan_4D and Plan_4D'. However, a statistically significant difference in target dose was observed between Plan_3D and Plan_3D' (P = 1.47 × 10⁻⁷) and between Plan_4D and Plan_4D' (P = 0.013). Plan_3D' meets 100% of the prescription dose covering mean 77.89% (SD 10.13%) of the Targeted_4D volume, while Plan_4D' covered mean 94.17% (SD 3.12%) of the Targeted_3D volume.

CONCLUSIONS

3D image-guided target delineation may be more likely to underestimate target volume and compromise dose coverage, suggesting that using multi-parametric 4D-MRI can provide more precise target contours and enhance target dose coverage.

Rapid dose prediction for lung CyberKnife radiotherapy plans utilizing a deep learning approach by incorporating dosimetric features delivered by noncoplanar beams

Purpose. The dose distribution of lung cancer patients treated with the CyberKnife (CK) system is influenced by various factors, including tumor location and the direction of CK beams. The objective of this study is to present a deep learning approach that integrates CK beam dose characteristics into CK planning dose calculations.Methods. The inputs utilized for the geometry and dosimetry method (GDM) include the patient's CT, the PTV structure, and multiple CK noncoplanar beam dose deposition features. The dose distributions were calculated using the Monte Carlo (MC) algorithm provided with the CK system and served as the ground truth dose label. Additionally, dose prediction was conducted through the geometry method (GM) for comparative analysis. The gamma pass rateγ(1 mm,1%),γ(2 mm,2%) andγ(3 mm,3%) were calculated between the predicted model and the MC method.Results. Compared to the GDM, the GM shows a significant dose difference from the MC approach in the low-dose region (<5 Gy) outside the target created by the various CK noncoplanar beams. The GDM increased theγ(1 mm, 1%) from 49.55% to 81.69%,γ(2 mm, 2%) from 73.24% to 98.11% and theγ(3 mm, 3%) from 81.69% to 99.37% when compared with the GM's results.Conclusions. This work proposed a deep learning dose calculation method by using patient geometry and dosimetry features in CK plans. The proposed method extends the geometric and dosimetric feature-driven deep learning dose calculation method to CK application scenarios, which has a great potential to accelerate the CK planning dose calculation and improve the planning efficiency.

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

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

Low-dose irradiation of the gut improves the efficacy of PD-L1 blockade in metastatic cancer patients

The mechanisms governing the abscopal effects of local radiotherapy in cancer patients remain an open conundrum. Here, we show that off-target intestinal low-dose irradiation (ILDR) increases the clinical benefits of immune checkpoint inhibitors or chemotherapy in eight retrospective cohorts of cancer patients and in tumor-bearing mice. The abscopal effects of ILDR depend on dosimetry (≥1 and ≤3 Gy) and on the metabolic and immune host-microbiota interaction at baseline allowing CD8+ T cell activation without exhaustion. Various strains of Christensenella minuta selectively boost the anti-cancer efficacy of ILDR and PD-L1 blockade, allowing emigration of intestinal PD-L1-expressing dendritic cells to tumor-draining lymph nodes. An interventional phase 2 study provides the proof-of-concept that ILDR can circumvent resistance to first- or second-line immunotherapy in cancer patients. Prospective clinical trials are warranted to define optimal dosimetry and indications for ILDR to maximize its therapeutic potential.

Anticipating potential bottlenecks in adaptive proton FLASH therapy: a ridge filter reuse strategy

Objective.Achieving FLASH dose rate with pencil beam scanning intensity modulated proton therapy is challenging. However, utilizing a single energy layer with a ridge filter (RF) can maintain dose rate and conformality. Yet, changes in patient anatomy over the treatment course can render the RF obsolete. Unfortunately, creating a new RF is time-consuming, thus, incompatible with online adaptation. To address this, we propose to re-optimize the spot weights while keeping the same initial RF.Approach.Data from six head and neck cancer patients with a repeated computed tomography (CT2) were used. FLASH treatment plans were generated with three methods on CT2: 'full-adaptation' (FA), optimized from scratch with a new RF; 'spot-adaptation only' (SAO), re-using initial RF but adjusting plan spot weights; and 'no adaptation' (NoA) where the dose from initial plans on initial CT (CT1) was recomputed on CT2. The prescribed dose per fraction was 9 Gy. Different beam angles were tested for each CT2(1 beam per fraction). The FA, SAO and NoA plans were then compared on CT2.Main results.Fractions with SAO showed a median decrease of 0.05 Gy forD98% and a median increase of 0.03 Gy forD2% of CTV when compared to their homologous FA plans on nominal case. Median conformity number decreased by 0.03. Median max dose to spinal cord increased by 0.09 Gy. The largest median increase in mean dose to organs was 0.03 Gy to the mandible. The largest observed median difference in organs receiving a minimal dose rate of 40 Gy s-1was 0.5% for the mandible. Up to 16 of the 20 evaluated SAO fractions were thus deemed clinically acceptable, with up to 8 NoA plans already acceptable before adaptation.Significance.Proposed SAO workflow showed that for most of our evaluated plans, daily reprinting of RF was not necessary.

Feasibility and safety study of ultra-hypofractionated neoadjuvant radiotherapy to margins-at-risk in retroperitoneal sarcoma

PURPOSE

Retroperitoneal sarcomas (RPS) are rare tumors that present unique challenges, often due to late presentation, and the proximity of critical organs makes complete surgical resection challenging. This study aimed to assess the feasibility of neoadjuvant short-course radiotherapy (SCRT) targeting margins-at-risk and to assess its potential impact on outcomes.

MATERIALS AND METHODS

This is a single-center, prospective, non-randomized feasibility study. SCRT was administered via image-guided volumetric modulated arc therapy, consisting of 5 fractions of daily radiotherapy followed by immediate surgery. As a starting dose, patients were prescribed 25 Gy in 5 fractions. For the escalation stage, patients were prescribed 30 Gy in 5 fractions. Only the presumed threatened surgical margins were delineated for large tumors.

RESULTS

Patients with either primary or recurrent RPS were recruited. Eight patients underwent SCRT but one patient did not have a resection as planned. Seven patients underwent surgical resection, of whom one passed away 3 months postoperative from a cardiac event. After a median follow-up of 20.5 months for the six postoperative survivors, there were no overt long-term toxicities and one patient relapsed out-of-radiotherapy-field.

CONCLUSION

SCRT to RPS with a margin boost followed by immediate surgery is worth investigating. A starting dose of 30 Gy in 5 fractions is recommended for further studies. Longer-term follow-up is necessary.

Low-Burden Oligometastatic Disease of the Lung Treated with Robotic Stereotactic Ablative Radiotherapy: A Retrospective Study

Background/Objectives: The lung is the most common site of metastases, regardless of the cancer subtype. Treating oligometastatic disease with surgery or stereotactic ablative radiotherapy (SABR) may improve patient survival. Methods: We retrospectively analyzed 41 patients with limited (one or two lesions, max dimension <3 cm) lung-only metastatic disease that were treated with the CK M6 robotic radiosurgery system in our Department, in terms of treatment efficacy and toxicity. Results: Acute and late toxicity was negligible (4 out of 41 patients developed grade 2 or 3 lung fibrosis). Six months post-SABR, complete response was achieved in 18 out of 41 patients (43.9%), while the rest of the cases exhibited major responses. A biological effective dose (BEDα/β=10) in the range of 100 Gy appears to be equally effective with higher doses. Within a median follow-up of 34 months, only three patients (7.3%) progressed locally, while three patients progressed to distal sites. Two-year local progression-free survival (LPFS) rates were 92.6% (95% CI 78.5-97%). Conclusions: SABR for low-burden lung oligometastases is an effective treatment modality that yields high local control and survival rates. Toxicity is negligible, regardless of the performance status of patients. Early referral of such patients to radiation oncology departments may be critical for patient survival and quality of life.

Planning Benchmark Study for Stereotactic Body Radiation Therapy of Pancreas Carcinomas With Simultaneously Integrated Boost and Protection: Results of the DEGRO/DGMP Working Group on Stereotactic Radiation Therapy and Radiosurgery

PURPOSE

The proximity or overlap of planning target volume (PTV) and organs-at-risk (OARs) poses a major challenge in stereotactic body radiation therapy (SBRT) of pancreatic cancer (PACA). This international treatment planning benchmark study investigates whether simultaneous integrated boost (SIB) and simultaneous integrated protection (SIP) concepts in PACA SBRT can lead to improved and harmonized plan quality.

METHODS AND MATERIALS

A multiparametric specification of desired target doses (gross target volume [GTV]D50%, GTVD99%, PTVD95%, and PTV0.5cc) with 2 prescription doses of GTVD50% = 5 × 9.2Gy (46 Gy) and GTVD50% = 8 × 8.25 Gy (66 Gy) and OAR limits were distributed with planning computed tomography and contours from 3 PACA patients. In phase 1, plans were ranked using a scoring system for comparison of trade-offs between GTV/PTV and OAR. In phase 2, replanning was performed for the most challenging case and prescription with dedicated SIB and SIP contours provided for optimization after group discussion.

RESULTS

For all 3 cases and both phases combined, 292 plans were generated from 42 institutions in 5 countries using commonly available treatment planning systems. The GTVD50% prescription was performed by only 76% and 74% of planners within 2% for 5 and 8 fractions, respectively. The GTVD99% goal was mostly reached, while the balance between OAR and target dose showed initial SIB/SIP-like optimization strategies in about 50% of plans. For plan ranking, 149 and 217 score penalties were given for 5 and 8 fractions, pointing to improvement possibilities. For phase 2, the GTVD50% prescription was performed by 95% of planners within 2%, and GTVD99% as well as OAR doses were better harmonized with notable less score penalties. Fourteen of 19 planners improved their plan rank, 9 of them by at least 2 ranks.

CONCLUSIONS

Dedicated SIB/SIP concepts in combination with multiparametric prescriptions and constraints can lead to overall harmonized and high treatment plan quality for PACA SBRT. Standardized SIB/SIP treatment planning in multicenter clinical trials appears feasible after group consensus and training.

Stereotactic arrhythmia radioablation for ventricular tachycardia: a review of clinical trials and emerging roles of imaging

Ventricular tachycardia (VT) is a severe arrhythmia commonly treated with implantable cardioverter defibrillators, antiarrhythmic drugs and catheter ablation (CA). Although CA is effective in reducing recurrent VT, its impact on survival remains uncertain, especially in patients with extensive scarring. Stereotactic arrhythmia radioablation (STAR) has emerged as a novel treatment for VT in patients unresponsive to CA, leveraging techniques from stereotactic body radiation therapy used in cancer treatments. Recent clinical trials and case series have demonstrated the short-term efficacy and safety of STAR, although long-term outcomes remain unclear. Imaging techniques, such as electroanatomical mapping, contrast-enhanced magnetic resonance imaging and nuclear imaging, play a crucial role in treatment planning by identifying VT substrates and guiding target delineation. However, challenges persist owing to the complex anatomy and variability in target volume definitions. Advances in imaging and artificial intelligence are expected to improve the precision and efficacy of STAR. The exact mechanisms underlying the antiarrhythmic effects of STAR, including potential fibrosis and improvement in cardiac conduction, are still being explored. Despite its potential, STAR should be cautiously applied in prospective clinical trials, with a focus on optimizing dose delivery and understanding long-term outcomes. Collaborative efforts are necessary to standardize treatment strategies and enhance the quality of life for patients with refractory VT.

Refining Treatment Planning in STereotactic Arrhythmia Radioablation: Benchmark Results and Consensus Statement From the STOPSTORM.eu Consortium

PURPOSE

STereotactic Arrhythmia Radioablation (STAR) showed promising results in patients with refractory ventricular tachycardia. However, clinical data are scarce and heterogeneous. The STOPSTORM.eu consortium was established to investigate and harmonize STAR in Europe. The primary goal of this benchmark study was to investigate current treatment planning practice within the STOPSTORM project as a baseline for future harmonization.

METHODS AND MATERIALS

Planning target volumes (PTVs) overlapping extracardiac organs-at-risk and/or cardiac substructures were generated for 3 STAR cases. Participating centers were asked to create single-fraction treatment plans with 25 Gy dose prescriptions based on in-house clinical practice. All treatment plans were reviewed by an expert panel and quantitative crowd knowledge-based analysis was performed with independent software using descriptive statistics for International Commission on Radiation Units and Measurements report 91 relevant parameters and crowd dose-volume histograms. Thereafter, treatment planning consensus statements were established using a dual-stage voting process.

RESULTS

Twenty centers submitted 67 treatment plans for this study. In most plans (75%) intensity modulated arc therapy with 6 MV flattening filter free beams was used. Dose prescription was mainly based on PTV D95% (49%) or D96%-100% (19%). Many participants preferred to spare close extracardiac organs-at-risk (75%) and cardiac substructures (50%) by PTV coverage reduction. PTV D0.035cm3 ranged from 25.5 to 34.6 Gy, demonstrating a large variety of dose inhomogeneity. Estimated treatment times without motion compensation or setup ranged from 2 to 80 minutes. For the consensus statements, a strong agreement was reached for beam technique planning, dose calculation, prescription methods, and trade-offs between target and extracardiac critical structures. No agreement was reached on cardiac substructure dose limitations and on desired dose inhomogeneity in the target.

CONCLUSIONS

This STOPSTORM multicenter treatment planning benchmark study not only showed strong agreement on several aspects of STAR treatment planning, but also revealed disagreement on others. To standardize and harmonize STAR in the future, consensus statements were established; however, clinical data are urgently needed for actionable guidelines for treatment planning.

Calculating optic nerve planning organ at risk volume margins for stereotactic radiosurgery using optic nerve motion determined using MRI

OBJECTIVES

The combination of sharp dose gradients in stereotactic radiosurgery (SRS) and minute optic nerve motion may significantly increase dose to the optic nerves when treating perioptic lesions. The aim of this study was to calculate optic nerve planning organ at risk volume (PRV) margins for CyberKnife SRS treatment planning.

METHODS

MRI scans were taken of 10 healthy volunteers looking left, right, up, down, and straight ahead to measure optic nerve motion. The measured optic nerve motion and the uncertainties in the technical accuracy of CyberKnife were used to calculate optic nerve PRV margins.

RESULTS

Two optic nerve PRV margins were calculated: a non-isotropic margin of mL/R,PRV=3 mm, mSup/Inf,PRV=2 mm, and mAnt/Post,PRV=1 mm which considers the full range of motion measured in a worst case scenario; and an isotropic margin of mPRV=1 mm which considers a scenario where patients are asked to look neutrally during imaging and treatment. Applying these PRVs to 8 historical sphenoid wing meningioma CyberKnife plans showed tolerance levels may be exceeded due to optic nerve motion.

CONCLUSIONS

Optic nerve PRV margins may be needed in CyberKnife planning to reduce risk to the optic nerves. The use of a mPRV=1 mm PRV to account for organ motion, along with instructing patients to hold their gaze neutrally during imaging and treatment, may be a suitable organ sparing strategy.

ADVANCES IN KNOWLEDGE

Measured optic nerve motion and the technical accuracy of the CyberKnife system have been used to calculate optic nerve PRV margins.

Accuracy-dependent dose-constraints and dose-based safety margins for organs-at-risk in radiotherapy

Background and purpose

Geometrical uncertainties in radiotherapy are generally accounted for by margins for tumors, but their effect on organs-at-risk (OARs) is often ignored. We developed a model that incorporates dose- and geometry-based uncertainties in OAR planning using dose constraints.

Materials and methods

Radiotherapy uncertainties cause real dose-volume histograms (DVHs) to spread around the planned DVH. With a published OAR dose constraint D(Vcrit) < Dcrit such that complication probability < Y%, real differences from planned Dcrit can be described by mean- (MDDcrit) and standard deviations (SDDcrit). Assuming complications are associated with the worst DVHs, New dose constraints that maintain complication probability can be derived for new treatments: Dcrit,New = Dcrit,publ + Φ-1(1 - Y%) * (SDDcrit,publ - SDDcrit,New) + (MDDcrit,publ - MDDcrit,New), with Φ-1(x) the inverse cumulative normal distribution function. Setting SDDcrit,New = MDDcrit,New = 0 in the recipe yields the "True" critical dose, and Dcrit,True - Dcrit,publ can be considered a dose-based safety margin (DSM).As hypothetical example, we estimated MDDcrit and SDDcrit values by simulating geometric errors in our clinical treatment plans and adding dose-based uncertainty. Over 1000 OARs with 108 different regular- and hypo-fractionation constraints were simulated. We assumed accuracy SDs to change from 2.5mm/3% to 1.5mm/2%.

Results

Results varied per OAR, fractionation, and constraint-type. If our 2.5mm/3% MDDcrit and SDDcrit values approximated dose-constraint studies, on average the DSM would be 4.5 Gy (18%) and our dose constraints would increase with 1.2 Gy (5%).

Conclusions

We introduced a first model relating dose constraints and complication probabilities with treatment uncertainties and safety margins for OARs. Among other things, it quantified how higher constraints can be applied with increasing radiotherapy accuracy.

Clinical Outcomes and Relevance of Composite V12 Gy in Patients With Four or More Brain Metastases Treated With Single Fraction Stereotactic Radiosurgery

AIMS

Tissue V12Gy (total brain volume receiving 12Gy including target) can predict for late toxicity in single target benign disease treated with stereotactic radiosurgery (SRS). The value of this metric remains uncertain for multiple brain metastases. This retrospective cohort study reports the outcomes and evaluates the predictors of toxicity in patients with four or more brain metastases treated with single-fraction SRS.

MATERIALS AND METHODS

Two hundred twenty-six patients with 2160 metastases treated from 2014-21 were retrospectively studied. Symptomatic late toxicity (new/progressive neurological symptoms ≥3 months post SRS) with magnetic resonance imaging (MRI) changes suggestive of treatment effect were analysed. Kaplan-Meier and competing risk analysis was used to assess survival and toxicity respectively.

RESULTS

median number of metastases/patient was 6 (range: 4-41) and median composite tissue V12Gy (inclusive of planning target volume (PTV)) was 11.3 cc (IQR: 6.1 cc-17.1 cc). Sixteen out of the 226 patients developed symptomatic late radiation adverse event (R-AE), and the cumulative incidence was 4.9% at 1 year and 6.9% at 2 years. The total target volume was significantly predictive of the risk of late R-AE. Volume of the largest lesion, V12Gy and V15Gy did not predict for late R-AE, but plotted graphs showed suggestions of linear relationships between dosimetric parameters and late R-AE.

CONCLUSION

Within the limitations of this study, the cumulative incidence of symptomatic toxicity remains acceptable despite routinely accepting a composite tissue V12Gy in excess of 10 cc to treat multiple brain metastases.

ADVANCES IN KNOWLEDGE

V12Gy has limitations as a plan quality metric in multiple brain metastases treated with SRS. There is insufficient evidence to have a defined target limit as <10 cc.

Dosimetric investigation of couch rotation angles in non-coplanar VMAT plans for lung cancer SBRT

Background

This study aimed to investigate the effect of couch rotation angles on non-coplanar volumetric modulated arc therapy (ncVMAT) plan for stereotactic body radiotherapy (SBRT) in lung cancer patients and to evaluate the feasibility of clinically applying ncVMAT for SBRT.

Methods

Twenty-four lung cancer patients with a single lesion eligible for SBRT were enrolled in the study. Seven dual partial-arc VMAT plans with varying couch angles were designed for every patient. These plans utilized two partial arcs, with the same first arc set at a fixed 0° couch angle in all plans. The second arc's couch angle varies at 15° intervals, ranging from 0° to 90°. The plans are designated as C0, NC15, NC30, NC45, NC60, NC75, and NC90, respectively. Plan evaluation included assessment of the maximum dose (Dmax), the mean dose (Dmean), homogeneity index (HI), conformity index (CI), and the ratio of the 50% isodose volume to the planning target volume (R50%). Dosimetric parameters for organs at risk such as the ipsilateral lung, contralateral lung, bilateral lungs, esophagus, trachea, chest wall, heart, and spinal cord were analyzed. Additionally, plan complexity-related metrics included modulation degree (MD), delivery time (DT), and monitor unit (MU) were assessed.

Results

As the couch rotation angle increased, parameters such as Dmax, Dmean, HI, CI, R50%, V20Gy, V25.75Gy and V30Gy of the ipsilateral lung and bilateral lungs, V10Gy of the contralateral lung and Dmean of the chest wall varied, while MD, MU, and DT increased. Compared to C0, the Dmax, Dmean, and HI of the planning target volume (PTV) decreased from 6728.35 ± 209.56cGy, 5743.04 ± 93.45cGy, and 0.281 ± 0.032 to 6500.48 ± 225.26cGy, 5654.81 ± 109.23cGy, and 0.245 ± 0.031, respectively, when the couch was rotated to 90°. The CI increased from 0.859 ± 0.031 to 0.876 ± 0.024. Decreases in R50% were 1.4%, 4.9%, 9%, 13.5%, 16.8%, and 18.4% for NC15, NC30, NC45, NC60, NC75, and NC90, respectively.

Conclusions

In the treatment of lung cancer using SBRT, ncVMAT plans demonstrate superior dose distribution and deliver lower doses to certain OARs compared to cVMAT plans. This advantage becomes more pronounced with increasing couch rotation angles. Our study offers theoretical support for the preferential use of ncVMAT plans in lung cancer SBRT and provides empirical evidence to guide the selection of optimal couch rotation angles.

Multi-institutional study using sbrt to treat mediastinal and hilar lymphadenopathy

Mediastinal and hilar lymphadenopathy (MHL) is a common pattern of cancer spread, particularly in lung disease. Recently, there has been interest in the use of SBRT for MHL, especially in the oligometastatic setting. The goal is to improve local control (LC) and to achieve shorter treatment durations to minimize systemic treatment interruptions. The primary endpoint of this study was local control (LC). The secondary endpoints were distant metastasis-free survival (DMFS), progression-free survival (PFS), and overall survival (OS) and predictive factors of response. This is a retrospective study. It analyses a group of patients treated with SBRT for MHL with different primary tumours and histologies. From November 2007 to June 2023, we treated 159 MHL in 128 patients. The primary most represented was lung cancer. A single fraction was used in 16% of cases and multiple fractions in 84% of cases. The medium BED 10 was 75.06 Gy (range: 37-120 Gy). Actuarial LC rates at 1, 2 and 5 years were 80.0%, 78.8% and 75.2%. The actuarial DMFS rates at 1, 2 and 5 years were 43.9%, 34.1% and 14.1%, respectively. Actuarial PFS rates at 1, 2 and 5 years were 37.2%, 23.9% and 8.3%, respectively. Actuarial OS rates at 1, 2 and 5 years were 68.8%, 52.7% and 26.9%, respectively. SBRT may be an option for the treatment of MHL. In addition, achieving a complete response is one of the most important predictors of our endpoints, in addition to tumour burden and volume.

Brachial plexopathy following stereotactic body radiation therapy in apical lung malignancies: A dosimetric pooled analysis of individual patient data

BACKGROUND AND OBJECTIVES

The aim of this study is to establish dosimetric constraints for the brachial plexus at risk of developing grade ≥ 2 brachial plexopathy in the context of stereotactic body radiation therapy (SBRT).

PATIENTS AND METHODS

Individual patient data from 349 patients with 356 apical lung malignancies who underwent SBRT were extracted from 5 articles. The anatomical brachial plexus was delineated following the guidelines provided in the atlases developed by Hall, et al. and Kong, et al.. Patient characteristics, pertinent SBRT dosimetric parameters, and brachial plexopathy grades (according to CTCAE 4.0 or 5.0) were obtained. Normal tissue complication probability (NTCP) models were used to estimate the risk of developing grade ≥ 2 brachial plexopathy through maximum likelihood parameter fitting.

RESULTS

The prescription dose/fractionation schedules for SBRT ranged from 27 to 60 Gy in 1 to 8 fractions. During a follow-up period spanning from 6 to 113 months, 22 patients (6.3 %) developed grade ≥2 brachial plexopathy (4.3 % grade 2, 2.0 % grade 3); the median time to symptoms onset after SBRT was 8 months (ranged, 3-54 months). NTCP models estimated a 10 % risk of grade ≥2 brachial plexopathy with an anatomic brachial plexus maximum dose (Dmax) of 20.7 Gy, 34.2 Gy, and 42.7 Gy in one, three, and five fractions, respectively. Similarly, the NTCP model estimates the risks of grade ≥2 brachial plexopathy as 10 % for BED Dmax at 192.3 Gy and EQD2 Dmax at 115.4 Gy with an α/β ratio of 3, respectively. Symptom persisted after treatment in nearly half of patients diagnosed with grade ≥2 brachial plexopathy (11/22, 50 %).

CONCLUSIONS

This study establishes dosimetric constraints ranging from 20.7 to 42.7 Gy across 1-5 fractions, aimed at mitigating the risk of developing grade ≥2 brachial plexopathy following SBRT. These findings provide valuable guidance for future ablative SBRT in apical lung malignancies.

ACROPath Oligometastases: The American College of Radiation Oncology Clinical Pathway

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

Feasibility of using contrast-free quantitative magnetic resonance imaging for liver sparing stereotactic ablative body radiotherapy

Background and purpose

Tumours in the liver often develop on a background of liver cirrhosis and impaired liver function. As a result, radiotherapy treatments are limited by radiation-induced liver disease, parameterised by the liver mean dose (LMD). Liver function is highly heterogeneous, especially in liver cancer, but the use of LMD does not take this into account. One possible way to improve liver treatments is to use quantitative imaging techniques to assess liver health and prioritise the sparing of healthy liver tissue.

Materials and methods

Anatomical T2 and quantitative iron-corrected T1 (cT1) images were made available for 10 patients with liver metastases. Functional liver volumes were automatically segmented on the quantitative images using a threshold. Liver stereotactic ablative body radiotherapy (SABR) plans were made using a departmental protocol. Liver-sparing plans were then made by reducing the dose to the functional sub-volume.

Results

The sparing plans achieved a statistically significant ( p = 0.002 ) reduction in the functional liver mean dose, with a mean reduction of 1.4 Gy. The LMD was also significantly different ( p = 0.002 ) but had a smaller magnitude with a mean reduction of 0.7 Gy. There were some differences in the planning target volume D99% ( p = 0.04 ) but the sparing plans remained within the optimal tolerance and the D95% was not significantly different ( p = 0.2 ).

Conclusions

This study has, for the first time, demonstrated the use of cT1 maps in radiotherapy showing significant reductions in dose to the healthy liver. Further work is needed to validate this in liver cancer patients, who would likely benefit most.

Stereotactic radiotherapy for liver oligometastases: a pooled analysis following the estro/eortc consensus recommendations

A large pooled analysis of liver oligometastases, classified accordingly to the ESTRO/EORTC recommendations, treated by stereotactic radiotherapy (SBRT) and Radiosurgery (SRS) was carried out. The clinical and dosimetric data of patients who underwent SBRT/SRS for liver metastases were analysed in terms of efficacy and toxicity profile. In particular, the Local Control (LC), the Distant Metastases Free Survival (DMFS), the Disease-Free Survival (DFS), the Overall Survival (OS), and the Next Systemic Therapy Free Survival (NEST-FS) rates were analysed. 113 patients (M/F: 49/64), accounting for a total of 150 hepatic lesions (March 2006-February 2023) in two Italian radiotherapy Institutions were evaluated. Median age was 67 years old (36-92) and 48 (42.5%) patients had at least one comorbidity. The majority of the lesions were induced (30.7%) or repeated oligoprogressive (12.7%) metastases. 98 lesions were treated with more than one daily fraction (mainly 50 Gy in 5 fractions), while 52 were radiosurgery treatments (mainly 32 Gy). The treatment response at 3-4 months was evaluable in 147 lesions: complete response was 32.0%, partial response 17.0%, and stable disease 32.0%. Actuarial LC, DMFS, DFS, OS, and NEST-FS at 1 year were 75.8%, 37.7%, 34.9%, 78.7%, and 59.4% respectively; while actuarial LC, DMFS, DFS, OS, and NEST-FS at 2 years were 52.1%, 24.9%, 21.9%, 51.3%, and 36.8%, respectively. The achievement of complete response, synchronous oligometastases, and no treatment interruptions correlated with a more favorable outcomes. As per the toxicity profile, we registered only two acute and one late toxicity cases higher than grade 2. Stereotactic treatment for liver metastases seems to be a safe and promising option in terms of local control. The best results in term of outcomes have been obtained in patients with complete response, synchronous oligometastases, favorable histology, and no treatment interruptions.

Dosimetric impact of the respiratory motion of the liver dome in stereotactic body radiotherapy for spine metastasis: A planning study

PURPOSE

This study aimed to clarify the dosimetric impact of the respiratory motion of the liver on stereotactic body radiation therapy (SBRT) for spine metastasis and examine the utility of introducing beam avoidance (beam-off at specific gantry angles).

METHODS

A total of 112 consecutive patients who underwent SBRT for spine metastasis between 2018 and 2024 were examined. Overall, 15 patients who had lesions near the liver dome were included in this study. Retrospective treatment plans were generated using computed tomography (CT) images acquired during inhalation and exhalation to evaluate the dosimetric impact of respiratory motion of the liver. The dose difference (DD) and relative value (DD%) were evaluated using the dose-volume histogram (DVH) metrics, planning target volume Dmax, D95%, spinal cord D0.035 cc, and esophagus D2.5 cc. The magnitude of the liver movements was evaluated based on differences of liver size Lave at the isocentric axial plane between the inspiratory and expiratory CT images.

RESULTS

The DD in almost all DVH metrics tended to increase when the liver moved away from the target during inhalation: For example, Mean ± $ \pm $ a standard deviation (SD) DD in PTV D95% for the treatment plan incorporating beam avoidance and those without beam avoidance was 0.5 ± $\pm$ 0.3 and 0.9 ± $ \pm $ 0.6 Gy, respectively. The spinal cord D0.035 cc for those shows 0.4 ± $ \pm $ 0.2 and 0.7 ± $ \pm $ 0.7 Gy, respectively. The treatment plans without beam avoidance also showed moderate or strong correlations between Lave and DD for almost all DVH metrics. No correlation was seen in the beam avoidance plan. The spinal cord D0.035 cc revealed approximately 1 Gy or +4% in DD when Lave was < -4 cm.

CONCLUSIONS

Respiratory motion of the liver dome can cause substantial dosimetric discrepancies in the dose delivered to the spinal cord, although the extent depends on patient variables. Dose assessment should be performed for determining the appropriate means of respiratory management, such as breath-hold. Alternatively, beam avoidance effectively mitigates the impact.

Lung and Liver Stereotactic Body Radiation Therapy During Mechanically Assisted Deep Inspiration Breath-Holds: A Prospective Feasibility Trial

Purpose

Radiation therapy for tumors subject to breathing-related motion during breath-holds (BHs) has the potential to substantially reduce the irradiated volume. Mechanically assisted and noninvasive ventilation (MANIV) could ensure the target repositioning accuracy during each BH while facilitating treatment feasibility through oxygen supplementation and a perfectly replicated mechanical support. However, there is currently no clinical evidence substantiating the use of MANIV-induced BH for moving tumors. The aim of this work was, therefore, to evaluate the technique's performance under real treatment conditions.

Methods and Materials

Patients eligible for lung or liver stereotactic body radiation therapy were prospectively included in a single-arm trial. The primary endpoint corresponded to the treatment feasibility with MANIV. Secondary outcomes comprised intrafraction geometric uncertainties extracted from real-time imaging, tolerance to BH, and treatment time.

Results

Treatment was successfully delivered in 92.9% (13/14) of patients: 1 patient with a liver tumor was excluded because of a mechanically induced gastric insufflation displacing the liver cranially by more than 1 cm. In the left-right/anteroposterior/craniocaudal directions, the recalculated safety margins based on intrafraction positional data were 4.6 mm/5.1 mm/5.6 mm and 4.7 mm/7.3 mm/5.9 mm for lung and liver lesions, respectively. Compared with the free-breathing internal target volume and midposition approaches, the average reduction in the planning target volume with MANIV reached -47.2% ± 15.3%, P < .001, and -29.4% ± 19.2%, P = .007, for intrathoracic tumors and -23.3% ± 12.4%, P < .001, and -9.3% ± 15.3%, P = .073, for upper abdominal tumors, respectively. For 1 liver lesion, large caudal drifts of occasionally more than 1 cm were measured. The total slot time was 53.1 ± 10.6 minutes with a BH comfort level of 80.1% ± 10.6%.

Conclusions

MANIV enables high treatment feasibility within a nonselected population. Accurate intrafraction tumor repositioning is achieved for lung tumors. Because of occasional intra-BH caudal drifts, pretreatment assessment of BH stability for liver lesions is, however, recommended.

Dose prescription for stereotactic body radiotherapy: general and organ-specific consensus statement from the DEGRO/DGMP Working Group Stereotactic Radiotherapy and Radiosurgery

PURPOSE AND OBJECTIVE

To develop expert consensus statements on multiparametric dose prescriptions for stereotactic body radiotherapy (SBRT) aligning with ICRU report 91. These statements serve as a foundational step towards harmonizing current SBRT practices and refining dose prescription and documentation requirements for clinical trial designs.

MATERIALS AND METHODS

Based on the results of a literature review by the working group, a two-tier Delphi consensus process was conducted among 24 physicians and physics experts from three European countries. The degree of consensus was predefined for overarching (OA) and organ-specific (OS) statements (≥ 80%, 60-79%, < 60% for high, intermediate, and poor consensus, respectively). Post-first round statements were refined in a live discussion for the second round of the Delphi process.

RESULTS

Experts consented on a total of 14 OA and 17 OS statements regarding SBRT of primary and secondary lung, liver, pancreatic, adrenal, and kidney tumors regarding dose prescription, target coverage, and organ at risk dose limitations. Degree of consent was ≥ 80% in 79% and 41% of OA and OS statements, respectively, with higher consensus for lung compared to the upper abdomen. In round 2, the degree of consent was ≥ 80 to 100% for OA and 88% in OS statements. No consensus was reached for dose escalation to liver metastases after chemotherapy (47%) or single-fraction SBRT for kidney primaries (13%). In round 2, no statement had 60-79% consensus.

CONCLUSION

In 29 of 31 statements a high consensus was achieved after a two-tier Delphi process and one statement (kidney) was clearly refused. The Delphi process was able to achieve a high degree of consensus for SBRT dose prescription. In summary, clear recommendations for both OA and OS could be defined. This contributes significantly to harmonization of SBRT practice and facilitates dose prescription and reporting in clinical trials investigating SBRT.

CT-guided online adaptive stereotactic body radiotherapy for pancreas ductal adenocarcinoma: Dosimetric and initial clinical experience

Purpose/Objectives

Retrospective analysis suggests that dose escalation to a biologically effective dose of more than 70 Gy may improve overall survival in patients with pancreatic ductal adenocarcinoma (PDAC), but such treatments in practice are limited by proximity of organs at risk (OARs). We hypothesized that CT-guided online adaptive radiotherapy (OART) can account for interfraction movement of OARs and allow for safe delivery of ablative doses.

Materials/Methods

This is a single institution retrospective analysis of patients with PDAC treated with OART on the Ethos platform (Varian Medical Systems, a Siemens Healthineers Company, Palo Alto). All patients were treated to 40 Gy in 5 fractions. PTV overlapping with a 5 mm planning risk volume expansion on the stomach, duodenum and bowel received 25 Gy. Initial treatment plans were created conventionally. For each fraction, PTV and OAR volumes were recontoured with AI assistance after initial cone beam CT (CBCT). The adapted plan was calculated, underwent QA, and then compared to the scheduled plan. A second CBCT was obtained prior to delivery of the selected plan. Total treatment time (first CBCT to end of radiation delivery) and active physician time (first to second CBCT) were recorded. PTV_4000 V95 %, PTV_2500 V9 5%, and D0.03 cc to stomach, duodenum and bowel were reported for scheduled (S) and adapted (A) plans. CTCAEv5.0 toxicities were recorded. Statistical analysis was performed using a two-sided T test and α of 0.05.

Results

21 patients with unresectable or locally-recurrent PDAC were analyzed, with a total of 105 fractions. Average total time was 29 min and 16 s (16:36-49:40) and average active physician time was 19:41 min (9:25-39:34). All fractions were treated with adapted plans. 97 % of adapted plans met PTV_4000 V95.0 % >95.0 % coverage goal and 100 % of adapted plans met OAR dose constraints. Median follow up was 6.6 months. Only 1 patient experienced acute grade 3+ toxicity directly attributable to radiation. Only 1 patient experienced late grade 3+ toxicity directly attributable to radiation.

Conclusions

Daily CT-based OART was associated with significantly reduced dose OARs while achieving superior PTV coverage. Given the relatively quick total treatment time, radiation delivery was generally well tolerated and easily incorporated into the clinic workflow. Our initial clinical experience demonstrates OART allows for safe dose escalation in the treatment of PDAC.

Technical note: MR image-based synthesis CT for CyberKnife robotic stereotactic radiosurgery

The purpose of this study is to investigate whether deep learning-based sCT images enable accurate dose calculation in CK robotic stereotactic radiosurgery. A U-net convolutional neural network was trained using 2446 MR-CT pairs and used it to translate 551 MR images to sCT images for testing. The sCT of CK patient was encapsulated into a quality assurance (QA) validation phantom for dose verification. The CT value difference between CT and sCT was evaluated using mean absolute error (MAE) and the statistical significance of dose differences between CT and sCT was tested using the Wilcoxon signed rank test. For all CK patients, the MAE value of the whole brain region did not exceed 25 HU. The percentage dose difference between CT and sCT was less than ±0.4% on GTV (D2(Gy), -0.29%, D95(Gy), -0.09%), PTV (D2(Gy), -0.25%, D95(Gy), -0.10%), and brainstem (max dose(Gy), 0.31%). The percentage dose difference between CT and sCT for most regions of interest (ROIs) was no more than ±0.04%. This study extended MR-based sCT prediction to CK robotic stereotactic radiosurgery, expanding the application scenarios of MR-only radiation therapy. The results demonstrated the remarkable accuracy of dose calculation on sCT for patients treated with CK robotic stereotactic radiosurgery.

Improving the Efficiency of Single-Isocenter Multiple Metastases Stereotactic Radiosurgery Treatment

Purpose

Multiple brain metastases can be treated efficiently with stereotactic radiosurgery (SRS) using a single-isocenter dynamic conformal arc (SIDCA) technique. Currently, plans are manually optimized, which may lead to unnecessary table angles and arcs being used. This study aimed to evaluate an automatic 4π optimization SIDCA algorithm for treatment efficiency and plan quality.

Methods and Materials

Automatic 4π-optimized SIDCA plans were created and compared with the manually optimized clinical plans for 54 patients who underwent single-fraction SRS for 2 to 10 metastases. The number of table angles and number of arcs were compared with a paired t test using a Bonferroni-corrected significance level of P < .05/4 = .0125. The reduction in treatment time was estimated from the difference in the number of table angles and arcs. Plan quality was assessed through the volume-averaged inverse Paddick Conformity Index (CI) and Gradient Index (GI) and the volume of normal brain surrounding each metastasis receiving 12 Gy (local V12 Gy). For a 5-patient subset, the automatic plans were manually adjusted further. CI and GI were assessed for noninferiority using a 1-sided t test with the noninferiority limit equal to the 95% interobserver reproducibility limit from a separate planning study (corrected significance level P < .05/[4 - 1] = .017).

Results

The automatic plans significantly improved treatment efficiency with a mean reduction in the number of table angles and arcs of -0.5 ± 0.1 and -1.3 ± 0.2, respectively (±SE; both P < .001). Estimated treatment time saving was -2.7 ± 0.5 minutes, 14% of the total treatment time. The volume-averaged CI and GI were noninferior to the clinical plans (both P < .001), although there was a small systematic shift in CI of 0.07 ± 0.01. The resulting difference in local V12 Gy, 0.25 ± 0.04 cm3, was not clinically significant. Minor manual adjustment of the automatic plans removed these slight differences while preserving the improved treatment efficiency.

Conclusions

Automatic 4π optimization can generate SIDCA SRS plans with improved treatment efficiency and noninferior plan quality.

Dosimetric comparison of IMPT vs VMAT for multiple lung lesions: an NTCP model-based decision-making strategy

To compare the dosimetric differences in volumetric modulated arc therapy (VMAT) and intensity modulated proton therapy (IMPT) in stereotactic body radiation therapy (SBRT) of multiple lung lesions and determine a normal tissue complication probability (NTCP) model-based decision strategy that determines which treatment modality the patient will use. A total of 41 patients were retrospectively selected for this study. The number of patients with 1-6 lesions was 5, 16, 7, 6, 3, and 4, respectively. A prescription dose of 70 GyRBE in 10 fractions was given to each lesion. SBRT plans were generated using VMAT and IMPT. All the IMPT plans used robustness optimization with ± 3.5% range uncertainties and 5 mm setup uncertainties. Dosimetric metrics and the predicted NTCP value of radiation pneumonitis (RP), esophagitis, and pericarditis were analyzed to evaluate the potential clinical benefits between different planning groups. In addition, a threshold for the ratio of PTV to lungs (%) to determine whether a patient would benefit highly from IMPT was determined using receiver operating characteristic curves. All plans reached target coverage (V70GyRBE ≥ 95%). Compared with VMAT, IMPT resulted in a significantly lower dose of most thoracic normal tissues. For the 1-2, 3-4 and 5-6 lesion groups, the lung V5 was 29.90 ± 9.44%, 58.33 ± 13.35%, and 81.02 ± 5.91% for VMAT and 11.34 ± 3.11% (p < 0.001), 21.45 ± 3.80% (p < 0.001), and 32.48 ± 4.90% (p < 0.001) for IMPT, respectively. The lung V20 was 12.07 ± 4.94%, 25.57 ± 6.54%, and 43.99 ± 11.83% for VMAT and 6.76 ± 1.80% (p < 0.001), 13.14 ± 2.27% (p < 0.01), and 19.62 ± 3.48% (p < 0.01) for IMPT. The Dmean of the total lung was 7.65 ± 2.47 GyRBE, 14.78 ± 2.75 GyRBE, and 21.64 ± 4.07 GyRBE for VMAT and 3.69 ± 1.04 GyRBE (p < 0.001), 7.13 ± 1.41 GyRBE (p < 0.001), and 10.69 ± 1.81 GyRBE (p < 0.001) for IMPT. Additionally, in the VMAT group, the maximum NTCP value of radiation pneumonitis was 73.91%, whereas it was significantly lower in the IMPT group at 10.73%. The accuracy of our NTCP model-based decision model, which combines the number of lesions and PTV/Lungs (%), was 97.6%. The study demonstrated that the IMPT SBRT for multiple lung lesions had satisfactory dosimetry results, even when the number of lesions reached 6. The NTCP model-based decision strategy presented in our study could serve as an effective tool in clinical practice, aiding in the selection of the optimal treatment modality between VMAT and IMPT.

Clinical impact of DVH uncertainties

Dose-volume histograms (DVH), along with dose and volume metrics, are central to radiotherapy planning. As such, errors have the potential to significantly impact the selection of appropriate treatment plans. Dose distributions that pass tests in one TPS may fail the same tests when transferred to another, even if using identical structures and dose grid information. This work shows the design and implementation of methods for assessing the accuracy of dose and volume computations performed by treatment planning systems (TPS), and other analytical tools. We demonstrate examples where differences in calculations between systems can change the assessment of a plan's clinical acceptability. Our work also provides a more detailed DVH analysis of single targets than earlier published studies. This is relevant for SRS plans and small structure dose assessments. Very small structures are a particular problem because of their coarse digital representation, and the impact of this is thoroughly examined. Reference DVH curves were derived mathematically, based on Gaussian dose distributions centered on spherical structures. The structures and dose distributions were generated synthetically, and imported into RayStation, MasterPlan, and ProKnow. Corresponding DVHs were analytically derived and taken as ground truth references, for comparison with the commercial DVH calculations. Two commonly used dose metrics PCI and MGI were used to determine the limit of calculation accuracy for small structures. In addition, to measure the DVH differences between a larger range of commercial DVH calculators, the D95 metric from a set of real clinical plans was compared across both the 3 DVH calculators under test, and across a further six TPSs from other hospitals. We show that even slight deviations between the results of DVH calculators can lead to plan check failures, and we illustrate this with the commonly used D95 planning metric. We present clinical data across eight planning systems that highlight instances where plan checks would pass in one software and fail in another due to DVH calculation differences. For the smallest volumes tested, errors of up to 20% were observed in the DVHs. RayStation was tested down to a 3 mm radius sphere (≈0.1 cc) and this showed close to 10% error, reducing to 1% for 10 mm radius (≈4.0 cc) and 0.1% for 20 mm radius (≈33 cc). In clinical plans, the variation in D95 was up to 9% for the smallest volumes, and typically around 2% in the range 0.5 cc-20 cc, and 1% in 20 cc-70 cc, falling to <0.1% for large volumes. Paddick Conformity Index (PCI) and Modified Gradient Index (MGI) are commonly used plan quality indicators for very small volumes. For volumes ≈0.1 cc we observed errors of up to 40% in PCI, and up to 75% in MGI. Our study extends the range of tested DVH calculators in published work, and shows their performance over a wider range of volume sizes. We provide quantitative evidence of the critical need to test the accuracy of DVH calculators in the TPS before clinical use. This work is particularly relevant for both stereotactic plan evaluation and for assessment of small volume doses in published dose constraint recommendations. We demonstrate that significant errors can occur in DVHs for volumes less than 1 cc, even if the volumes themselves are calculated accurately. Even for large structures, deviations between the outputs of DVH calculators can lead to indicated or reported plan check failures if they do not include appropriate tolerances. We urge caution in the use of DVH metrics for these very small volumes and recommend that appropriate DVH uncertainty tolerances are set in organ dose constraints when using them to evaluate clinical plans.

Treatment planning and delivery practice of lung SBRT: Results of the 2022 ESTRO physics survey

BACKGROUND AND PURPOSE

The use of Stereotactic Body Radiation Therapy (SBRT) in lung cancer is increasing. However, there is no consensus on the most appropriate treatment planning and delivery practice for lung SBRT. To gauge the range of practice, quantify its variability and identify where consensus might be achieved, ESTRO surveyed the medical physics community.

MATERIALS AND METHODS

An online survey was distributed to ESTRO's physicist membership in 2022, covering experience, dose and fractionation, target delineation, dose calculation and planning practice, imaging protocols, and quality assurance.

RESULTS

Two-hundred and forty-four unique answers were collected after data cleaning. Most respondents were from Europe the majority of which had more than 5 years' experience in SBRT. The large majority of respondents deliver lung SBRT with the VMAT technique on C-arm Linear Accelerators (Linacs) employing daily pre-treatment CBCT imaging. A broad spectrum of fractionation schemes were reported, alongside an equally wide range of dose prescription protocols. A clear preference was noted for prescribing to 95% or greater of the PTV. Several issues emerged regarding the dose calculation algorithm: 22% did not state it while 24% neglected to specify the conditions under which the dose was calculated. Contouring was usually performed on Maximum or Average Intensity Projection images while dose was mainly computed on the latter. No clear indications emerged for plan homogeneity, complexity, and conformity assessment. Approximately 40% of the responders participated in inter-centre credentialing of SBRT in the last five years. Substantial differences emerged between high and low experience centres, with the latter employing less accurate algorithms and older equipment.

CONCLUSION

The survey revealed an evident heterogeneity in numerous aspects of the clinical implementation of lung SBRT treatments. International guidelines and codes of practice might promote harmonisation.

Application and dosimetric comparison of surface-guided deep inspiration breath-hold for lung stereotactic body radiotherapy

Respiratory motion management is the crucial challenge for safe and effective application of lung stereotactic body radiotherapy (SBRT). The present study implemented lung SBRT treatment in voluntary deep inspiration breath-hold (DIBH) with surface-guided radiotherapy (SGRT) system and evaluated the geometric and dosimetric benefits of DIBH to organs-at-risk (OARs), aiming to advising the choice between DIBH technology and conventional free breathing 4 dimensions (FB-4D) technology. Five patients of lung SBRT treated in DIBH with SGRT at our institution were retrospectively analyzed. CT scans were acquired in DIBH and FB-4D, treatment plans were generated for both respiratory phases. The geometric and dosimetry of tumor, ipsilateral lung, double lungs and heart were compared between the DIBH and FB-4D treatment plans. In terms of target coverage, utilizing DIBH significantly reduced the mean plan target volume (PTV) by 21.9% (p = 0.09) compared to FB-4D, the conformity index (CI) of DIBH and FB-4D were comparable, but the dose gradient index (DGI) of DIBH was higher. With DIBH expanding lung, the volumes of ipsilateral lung and double lungs were 2535.1 ± 403.0cm3 and 4864.3 ± 900.2cm3, separately, 62.2% (p = 0.009) and 73.1% (p = 0.009) more than volumes of ipsilateral lung (1460.03 ± 146.60cm3) and double lungs (2811.25 ± 603.64cm3) in FB-4D. The heart volume in DIBH was 700.0 ± 146.1cm3, 11.6% (p = 0.021) less than that in FB-4D. As for OARs protection, the mean dose, percent of volume receiving > 20Gy (V20) and percent of volume receiving > 5Gy (V5) of ipsilateral lung in DIBH were significantly lower by 33.2% (p = 0.020), 44.0% (p = 0.022) and 24.5% (p = 0.037) on average, separately. Double lungs also showed significant decrease by 31.1% (p = 0.019), 45.5% (p = 0.024) and 20.9% (p = 0.048) on average for mean dose, V20 and V5 in DIBH. Different from the lung, the mean dose and V5 of heart showed no consistency between DIBH and FB-4D, but lower maximum dose of heart was achieved in DIBH for all patients in this study. Appling lung SBRT in DIBH with SGRT was feasibly performed with high patient compliance. DIBH brought significant dosimetric benefits to lung, however, it caused more or less irradiated heart dose that depend on the patients' individual differences which were unpredictable.

Clinical Outcomes of Online Adaptive Magnetic Resonance-Guided Stereotactic Body Radiotherapy of Adrenal Metastases from a Single Institution

(1) Background: Recent publications foster stereotactic body radiotherapy (SBRT) in patients with adrenal oligometastases or oligoprogression. However, local control (LC) after non-adaptive SBRT shows the potential for improvement. Online adaptive MR-guided SBRT (MRgSBRT) improves tumor coverage and organ-at-risk (OAR) sparing. Long-term results of adaptive MRgSBRT are still sparse. (2) Methods: Adaptive MRgSBRT was performed on a 0.35 T MR-Linac. LC, overall survival (OS), progression-free survival (PFS), overall response rate (ORR), and toxicity were assessed. (3) Results: 35 patients with 40 adrenal metastases were analyzed. The median gross tumor volume was 30.6 cc. The most common regimen was 10 fractions at 5 Gy. The median biologically effective dose (BED10) was 75.0 Gy. Plan adaptation was performed in 98% of all fractions. The median follow-up was 7.9 months. One local failure occurred after 16.6 months, resulting in estimated LC rates of 100% at one year and 90% at two years. ORR was 67.5%. The median OS was 22.4 months, and the median PFS was 5.1 months. No toxicity > CTCAE grade 2 occurred. (4) Conclusions: LC and ORR after adrenal adaptive MRgSBRT were excellent, even in a cohort with comparably large metastases. A BED10 of 75 Gy seems sufficient for improved LC in comparison to non-adaptive SBRT.

Radiation-Induced Sensorineural Hearing Loss and Potential Management

The cochlear apparatus is one of the major organs at risk when considering radiation therapy (RT) for brain, head, and neck tumors. Radiation oncologists currently consider mean dose constraints of <35 Gy for conventionally fractioned radiation therapy (RT), <4 Gy for single fraction stereotactic radiosurgery, and <17.1 or 25 Gy for 3- or 5-fraction stereotactic radiosurgery, respectively, as the standard of care. Indeed, dose adjustments are made in the setting of concurrent platinum-based chemotherapy or when prioritizing tumor coverage during treatment planning. Despite guidelines, in many patients, RT to the cochlea may still cause sensorineural hearing loss through progressive degeneration and ossification of the inner ear. There are several audiologic and otolaryngologic interventions for incident RT-induced hearing loss, including hearing aids, cochlear implants, or, in the context of vestibular schwannoma due to neurofibromatosis type 2, auditory brain stem implantation. Cochlear implants are the most effective at restoring hearing and improving quality of life for those with an intact cochlear nerve. An early multidisciplinary approach is essential to optimally manage RT-induced hearing loss, and this topic discussion serves as a guide for radiation oncologists on cochlear dosimetric considerations as well as how to address potential RT-induced adverse effects.

REPeated mAgnetic resonance Image-guided stereotactic body Radiotherapy (MRIg-reSBRT) for oligometastatic patients: REPAIR, a mono-institutional retrospective study

BACKGROUND

Oligo-progression or further recurrence is an open issue in the multi-integrated management of oligometastatic disease (OMD). Re-irradiation with stereotactic body radiotherapy (re-SBRT) technique could represent a valuable treatment option to improve OMD clinical outcomes. MRI-guided allows real-time visualization of the target volumes and online adaptive radiotherapy (oART). The aim of this retrospective study is to evaluate the efficacy and toxicity profile of MRI-guided repeated SBRT (MRIg-reSBRT) in the OMD setting and propose a re-SBRT classification.

METHODS

We retrospectively analyzed patients (pts) with recurrent liver metastases or abdominal metastatic lesions between 1 and 5 centimeters from liver candidate to MRIg-reSBRT showing geometric overlap between the different SBRT courses and assessing whether they were in field (type 1) or not (type 2).

RESULTS

Eighteen pts completed MRIg-reSBRT course for 25 metastatic hepatic/perihepatic lesions from July 2019 to January 2020. A total of 20 SBRT courses: 15 Type 1 re-SBRT (75%) and 5 Type 2 re-SBRT (25%) was delivered. Mean interval between the first SBRT and MRIg-reSBRT was 8,6 months. Mean prescribed dose for the first treatment was 43 Gy (range 24-50 Gy, mean BEDα/β10=93), while 41 Gy (range 16-50 Gy, mean BEDα/β10=92) for MRIg-reSBRT. Average liver dose was 3,9 Gy (range 1-10 Gy) and 3,7 Gy (range 1,6-8 Gy) for the first SBRT and MRIg-reSBRT, respectively. No acute or late toxicities were reported at a median follow-up of 10,7 months. The 1-year OS and PFS was 73,08% and 50%, respectively. Overall Clinical Benefit was 54%.

CONCLUSIONS

MRIg-reSBRT could be considered an effective and safe option in the multi-integrated treatment of OMD.

An in-silico planning study of stereotactic body radiation therapy for polymetastatic patients with more than ten extra-cranial lesions

Background and purpose

Limited data is available about the feasibility of stereotactic body radiation therapy (SBRT) for treating more than five extra-cranial metastases, and almost no data for treating more than ten. The aim of this study was to investigate the feasibility of SBRT in this polymetatstatic setting.

Materials and methods

Consecutive metastatic melanoma patients with more than ten extra-cranial metastases and a maximum lesion diameter below 11 cm were selected from a single-center prospective registry for this in-silico planning study. For each patient, SBRT plans were generated to treat all metastases with a prescribed dose of 5x7Gy, and dose-limiting organs (OARs) were analyzed. A cell-kill based inverse planning approach was used to automatically determine the maximum deliverable dose to each lesion individually, while respecting all OARs constraints.

Results

A total of 23 polymetastatic patients with a medium of 17 metastases (range, 11-51) per patient were selected. SBRT plans with sufficient target coverage and respected OARs dose constraints were achieved in 16 out of 23 patients. In the remaining seven patients, the lungs V5Gy < 80 % and the liver D700 cm3 < 15Gy were most frequently the dose-limiting constraints. The cell-kill based planning approach allowed optimizing the dose administration depending on metastases total volume and location.

Conclusion

This retrospective planning study shows the feasibility of definitive SBRT for 70% of polymetastatic patients with more than ten extra-cranial lesions and proposes the cell-killing planning approach as an approach to individualize treatment planning in polymetastatic patients'.

Biochemical Safety of SBRT to Multiple Intrahepatic Lesions for Hepatocellular Carcinoma

Background

We aim to better characterize stereotactic body radiation therapy (SBRT)-related hepatic biochemical toxicity in patients with multiple intrahepatic lesions from hepatocellular carcinoma (HCC).

Methods

We conducted a retrospective analysis of patients with HCC who underwent SBRT for 2 or more synchronous or metachronous liver lesions. We collected patient characteristics and dosimetric data (mean liver dose [MLD], cumulative effective volume [Veff], cumulative volume of liver receiving 15 Gy [V15Gy], and cumulative planning target volume [PTV]) along with liver-related toxicity (measured by albumin-bilirubin [ALBI] and Child-Pugh [CP] scores). A linear mixed-effects model was used to assess the effect of multi-target SBRT on changes in ALBI.

Results

There were 25 patients and 56 lesions with median follow-up of 29 months. Eleven patients had synchronous lesions, and 14 had recurrent lesions treated with separate SBRT courses. Among those receiving multiple SBRT courses, there were 7 lesions with overlap of V15Gy (median V15Gy overlap: 35 mL, range: 0.5-388 mL). There was no association between cumulative MLD, Veff, V15Gy, or PTV and change in ALBI. Four of 25 patients experienced non-classic radiation-induced liver disease (RILD), due to an increase of CP score by ≥2 points 3 to 6 months after SBRT. Sixteen of 25 patients experienced an increase in ALBI grade by 1 or more points 3 to 6 months after SBRT. Comparing the groups that received SBRT in a single course versus multiple courses revealed no statistically significant differences in liver toxicity.

Conclusion

Liver SBRT for multiple lesions in a single or in separate courses is feasible and with acceptable risk of hepatotoxicity. Prospective studies with a larger cohort are needed to better characterize safety in this population.

Hyperfractionated Accelerated Radiotherapy Versus Stereotactic Body Radiotherapy in the Treatment of Limited-Stage Small Cell Lung Cancer: A Matched-Pair Analysis

BACKGROUND

Concurrent chemoradiotherapy based on hyperfractionated accelerated radiotherapy (HART) is the first-line recommended regimen for the treatment of small-cell lung cancer (SCLC). However, Stereotactic Body Radiotherapy (SBRT) is also regarded as an effective treatment for limited-stage (LS) SCLC, and the efficacy and safety of HART versus SBRT stay controversial.

METHODS

In this study, 188 LS-SCLC patients were retrospectively divided into two groups receiving chemotherapy combined with either HART or SBRT. In HART group, patients received 4500 cGy in 30 fractions, administered twice daily for 3 weeks. Whereas in the SBRT group, a total radiation dose of 4000-4500 cGy was delivered in 10 fractions over 2 weeks. Thirty-three pairs of patients were finally included for next analysis.

RESULTS

The estimated objective response rates were 63.6 % (21/33) and 78.8 % (26/33) in HART group and SBRT group, respectively (P = 0.269). Furthermore, there was no significant difference between HART and SBRT groups in overall survival (26 months vs. 29 months, P = 0.362) and progression free survival (11 months vs. 15 months, P = 0.223). As for the adverse events, toxicity of both groups is similar and slight that no grade 4 event was observed. Grade 3 pneumonitis cases were all occurred in the HART group (9.1%, 3/33, P = 0.238), and grade 3 esophagitis cases were all occurred in the SBRT group (6.1%, 2/33, P = 0.492).

CONCLUSION

Compared with HART, SBRT could be another effective treatment with satisfactory safety for the concurrent chemoradiotherapy in patients with LS-SCLC.

4D-MRI assisted stereotactic body radiation therapy for unresectable colorectal cancer liver metastases

This study evaluated the feasibilities and outcomes following four-dimensional magnetic resonance imaging (4D-MRI) assisted stereotactic body radiation therapy (SBRT) for unresectable colorectal liver metastases (CRLMs). From March 2018 to January 2022, we identified 76 unresectable CRLMs patients with 123 lesions who received 4D-MRI guided SBRT in our institution. 4D-MRI simulation with or without abdominal compression was conducted for all patients. The prescription dose was 50-65 Gy in 5-12 fractions. The image quality of computed tomography (CT) and MRI were compared using the Clarity Score. Clinical outcomes and toxicity profiles were evaluated. 4D-MRI improved the image quality compared with CT images (mean Clarity Score: 1.67 vs 2.88, P < 0.001). The abdominal compression reduced motions in cranial-caudal direction (P = 0.03) with two phase T2 weighted images assessing tumor motion. The median follow-up time was 12.5 months. For 98 lesions assessed for best response, the complete response, partial response and stable disease rate were 57.1 %, 30.6 % and 12.2 %, respectively. The local control (LC) rate at 1 year was 97.3 %. 46.1 % of patients experienced grade 1-2 toxicities and only 2.6 % patients experienced grade 3 hematologic toxicities. The 4D-MRI technique allowed accurate target delineation and motion tracking in unresectable CRLMs patients. Favorable LC rate and mild toxicities were achieved. This study provided evidence for using 4D-MRI assisted SBRT as an alternative treatment in unresectable CRLMs.

Predictive clinical and dosimetric parameters for risk of relapse in early-stage non-small cell lung cancer treated by SBRT: A large single institution experience

Purpose

To evaluate the impact of dosimetric parameters on efficacy of stereotactic body radiation therapy (SBRT) in early-stage non-small cell lung cancer (ES-NSCLC), using Hypofractionated Treatment Effects in the Clinic (HyTEC) reporting standards.

Methods

From April 2010 to December 2020, 497 patients who received SBRT for ES-NSCLC at the University Hospital of Liège were retrospectively enrolled. A total dose of 40 to 60 Gy in 3-5 fractions (72-180 Gy biologically effective dose with an α/β ratio of 10 (BED10)) was prescribed to the 80 % isodose line of the PTV. Potential clinical and dosimetric predictors of recurrence, overall survival (OS) and disease specific survival (DSS) were evaluated using univariate and multivariate analyses.

Results

After a median follow-up of 32 months (range 3-143 months), the local control and disease-free survival (DFS) rates at 3 years were 91 % (95 % CI: 90 %-93 %) and 75 % (95 % CI: 73 %-77 %), respectively. The median OS was 41.6 months and the median DSS was not reached. On multivariate analysis, a higher gross tumor volume (GTV) Dmax (BED10) (cut-off 198 Gy) and a larger percent of the GTV receiving ≥110 % of the prescribed dose were predictive of a better local control, only GTV volume was correlated with DSS and no parameter was correlated with OS and regional or distant recurrences.

Conclusion

Lung SBRT for ES-NSCLC in 3 to 5 fractions resulted in high local control rates. A higher percent of GTV receiving ≥110 % of the prescribed dose and a higher GTV Dmax (BED10) seem to allow a better local control.

Stereotactic body radiotherapy in lung cancer: a contemporary review

The treatment of early stage non-small cell lung cancer (NSCLC) has improved enormously in the last two decades. Although surgery is not the only choice, lobectomy is still the gold standard treatment type for operable patients. For inoperable patients stereotactic body radiotherapy (SBRT) should be offered, reaching very high local control and overall survival rates. With SBRT we can precisely irradiate small, well-defined lesions with high doses. To select the appropriate fractionation schedule it is important to determine the size, localization and extent of the lung tumor. The introduction of novel and further developed planning (contouring guidelines, diagnostic image application, planning systems) and delivery techniques (motion management, image guided radiotherapy) led to lower rates of side effects and more conformal target volume coverage. The purpose of this study is to summarize the current developments, randomised studies, guidelines about lung SBRT, with emphasis on the possibility of increasing local control and overall rates in "fit," operable patients as well, so SBRT would be eligible in place of surgery.

Evaluating dose coverage and conformity in stereotactic ablative body radiotherapy (SABR) plans

PURPOSE

Accepted conformity metrics in stereotactic ablative body radiotherapy (SABR) have significant limitations. This work aimed to develop a spatial assessment methodology that improves and automates checks of dose prescription and dose gradient from planning target volume (PTV) edge.

METHODS

A Python-based script was developed to determine linear distances from the PTV edge to specified isodose, every 15 degrees on all axial slices and along the central axis in the coronal plane. A new "Internal PTV contour" distance metric is introduced as a size and shape indicator. 134 previously treated SABR patients stratified by anatomical site and PTV volume were analysed to establish baselines and tolerances for automation acceptability.

RESULTS

In the axial plane, median distance (MD) from PTV edge to the 100 % isodose was 0.13 mm (range: -0.67 to 0.53 mm), and for the 90 % isodose was 2.37 mm (1.36 to 3.40 mm). Lung and non-Lung dose gradient criteria was established by fitting a second order polynomial to the MD as a function of "Internal PTV contour". This resulted in acceptability criteria of MD + 1 mm for 80 % isodose and MD + 2 mm for the 50 % isodose. For the coronal plane, MD to the 100 % isodose was 0.49 mm (-1.24 to 2.14 mm) and for the 90 % was 1.73 mm (-0.49 to 4.13 mm).

CONCLUSIONS

Our in-house script enables a high-quality spatial assessment of PTV dose coverage and gradient, with the new 'Internal PTV contour' distance metric correlating well with dose gradient.

Stereotactic body radiation therapy for liver metastases in oligometastatic disease

Oligometastatic cancers designate cancers in which the number of metastases is less than five, corresponding to a particular biological entity whose prognosis is situated between a localized and metastatic disease. The liver is one of the main sites of metastases. When patients are not suitable for surgery, stereotactic body radiotherapy provides high local control rate, although these data come mainly from retrospective studies, with no phase III study results. The need for a high therapeutic dose (biologically effective dose greater than 100Gy) while respecting the constraints on the organs at risk, and the management of respiratory movements require expertise and sufficient technical prerequisites. The emergence of new techniques such as MRI-guided radiotherapy could further increase the effectiveness of stereotactic radiotherapy of liver metastases, and thus improve the prognosis of these oligometastatic cancers.

Dosimetric verification of four dose calculation algorithms for spine stereotactic body radiotherapy

The applications of Type B [anisotropic analytical algorithm (AAA) and collapsed cone (CC)] and Type C [Acuros XB (AXB) and photon Monte Carlo (PMC)] dose calculation algorithms in spine stereotactic body radiotherapy (SBRT) were evaluated. Water- and bone-equivalent phantoms were combined to evaluate the percentage depth dose and dose profile. Subsequently, 48 consecutive patients with clinical spine SBRT plans were evaluated. All treatment plans were created using AXB in Eclipse. The prescription dose was 24 Gy in two fractions at a 10 MV FFF on TrueBeam. The doses were then recalculated with AAA, CC and PMC while maintaining the AXB-calculated monitor units and beam arrangement. The dose index values obtained using the four dose calculation algorithms were then compared. The AXB and PMC dose distributions agreed with the bone-equivalent phantom measurements (within ±2.0%); the AAA and CC values were higher than those in the bone-equivalent phantom region. For the spine SBRT plans, PMC, AAA and CC were overestimated compared with AXB in terms of the near minimum and maximum doses of the target and organ at risk, respectively; the mean dose difference was within 4.2%, which is equivalent with within 1 Gy. The phantom study showed that the results from AXB and PMC agreed with the measurements within ±2.0%. However, the mean dose difference ranged from 0.5 to 1 Gy in the spine SBRT planning study when the dose calculation algorithms changed. Users should incorporate a clinical introduction that includes an awareness of these differences.

Small Bowel Dose Constraints in Radiation Therapy—Where Omics-Driven Biomarkers and Bioinformatics Can Take Us in the Future

Radiation-induced gastrointestinal (GI) dose constraints are still a matter of concern with the ongoing evolution of patient outcomes and treatment-related toxicity in the era of image-guided intensity-modulated radiation therapy (IMRT), stereotactic ablative radiotherapy (SABR), and novel systemic agents. Small bowel (SB) dose constraints in pelvic radiotherapy (RT) are a critical aspect of treatment planning, and prospective data to support them are scarce. Previous and current guidelines are based on retrospective data and experts’ opinions. Patient-related factors, including genetic, biological, and clinical features and systemic management, modulate toxicity. Omic and microbiome alterations between patients receiving RT to the SB may aid in the identification of patients at risk and real-time identification of acute and late toxicity. Actionable biomarkers may represent a pragmatic approach to translating findings into personalized treatment with biologically optimized dose escalation, given the mitigation of the understood risk. Biomarkers grounded in the genome, transcriptome, proteome, and microbiome should undergo analysis in trials that employ, R.T. Bioinformatic templates will be needed to help advance data collection, aggregation, and analysis, and eventually, decision making with respect to dose constraints in the modern RT era.

Short-term pain control after palliative radiotherapy for uncomplicated bone metastases: a prospective cohort study

This study aimed at evaluating the efficacy of different radiotherapy (RT) fractionation regimens in managing uncomplicated painful bone metastases (BM) and identifying predictive factors for pain control. Patients with 1 to 4 symptomatic BM from any primary solid tumors and a life expectancy exceeding 3 months were included in the study and received palliative RT, with SBRT restricted in the context of oligometastatic disease or in patients with good prognosis. Pain analysis using the Brief Pain Inventory (BPI) tool was conducted at baseline, 1 and 3 months after RT. Analgesic intake was recorded as morphine-equivalent doses (OME). Pain response was assessed using the International Consensus on Palliative Radiotherapy Endpoint (ICPRE). Multivariate logistic regression analyzed patient-related, tumor-related, and treatment-related factors predicting BM pain control at 3 months post-RT. From Feb 2022 to Feb 2023, 44 patients with 65 symptomatic BM were investigated. Breast (32%) and lung (24%) tumors were the most common primary tumors. Treatment plans included 3DCRT (60%) and VMAT (40%), with a median biological effective dose for tumors (BED) of 29 Gy [14-108]. All patients completed the 3-month follow-up. Pain response rates were 62% at 1 month and 60% at 3 months. Responders had better PS ECOG scores (67%; P = 0.008) and received active systemic therapies (67%: P = 0.036). Non-responders had lower pretreatment BPI (mean: 13.7 vs. 58.2; P = 0.032), with significantly higher values after 1 month (mean: 9.1 vs. 5.3, P = 0.033). Baseline BPI (OR: 1.17; 95% CI: 1.032-1.327; P = 0.014) and BPI at 1 month (OR: 0.83; 95% CI: 0.698-0.976; P = 0.025) were independent predictors of pain response at 3 months. Our findings show that palliative RT ensured short-term pain control in patients with BM, regardless of tumor type and dose-fractionation regimen. A larger sample size and a longer follow-up could potentially identify which patients are likely to benefit most from RT, and which fractionation might be indicated for achieving a durable pain relief. A multidisciplinary approach is paramount to provide a better care to BM patients.

Stereotactic Body Radiotherapy for Spine Oligometastases: A Multicentre Retrospective Study From the Italian Association of Radiotherapy and Clinical Oncology (AIRO)

AIM

To evaluate the efficacy of stereotactic body radiotherapy (SBRT) for spine oligometastases.

MATERIALS AND METHODS

This was a multicentre retrospective study of a series of patients who received SBRT for spine oligometastases. The efficacy of SBRT was evaluated in terms of local control as the primary endpoint. Survival outcomes were also analysed to identify predictive factors for clinical outcomes. Toxicity was assessed according to CTCAE v4.0.

RESULTS

Between March 2018 and July 2022, 183 lesions in 177 patients were analysed. In most patients, SBRT was delivered to a single spine metastasis (82%) for a median total dose of 21 Gy (14-35 Gy) in three fractions (one to five fractions) and a median BED10 = 119 Gy (57.7-152 Gy). Local control rates were 90.3% at 1 year, 84.3% at 2 years and 84.3% at 3 years. Distant progression-free survival rates were 33.1%, 18.5% and 12.4% at 1, 2 and 3 years, with prostate histology (P = 0.023), oligorecurrent disease (P = 0.04) and BED10 > 100 Gy (P = 0.04) found to be predictive on univariate analysis. A further oligometastatic progression was observed in 33 patients (18.6%) treated with a second course of SBRT, reporting at univariate analysis improved overall survival rates (P = 0.01). Polymetastases-free survival rates were 57.8%, 43.4% and 32.4%; concurrent therapy was related to improved outcomes at multivariate analysis (P = 0.009). Overall survival rates were 91.8%, 79.6% and 65.9%, with prostate histology and non-cervical metastases related to better overall survival at multivariate analysis. Pain-flare after SBRT was recorded in 3.3%; five patients underwent surgical decompression after SBRT; there were no grade ≥3 adverse events.

CONCLUSIONS

In our experience of only oligometastatic patients, spine SBRT gave excellent results in terms of safety and efficacy. Prostate histology and oligorecurrent disease were predictive factors for improved clinical outcomes; also, patients who experienced a further oligoprogression after SBRT maintained a survival advantage compared with polymetastatic progression. No severe adverse events were reported.

Five-Fraction Proton Therapy for the Treatment of Skull Base Chordomas and Chondrosarcomas: Early Results of a Prospective Series and Description of a Clinical Trial

(1) Background: Our purpose is to describe the design of a phase II clinical trial on 5-fraction proton therapy for chordomas and chondrosarcomas of the skull base and to present early results in terms of local control and clinical tolerance of the first prospective series. (2) Methods: A dose of 37.5 GyRBE in five fractions was proposed for chordomas and 35 GyRBE in five fractions for chondrosarcomas. The established inclusion criteria are age ≥ 18 years, Karnofsky Performance Status ≥ 70%, clinical target volume up to 50 cc, and compliance with dose restrictions to the critical organs. Pencil beam scanning was used for treatment planning, employing four to six beams. (3) Results: A total of 11 patients (6 chordomas and 5 chondrosarcomas) were included. The median follow-up was 12 months (9-15 months) with 100% local control. Acute grade I-II headache (64%), grade I asthenia and alopecia (45%), grade I nausea (27%), and grade I dysphagia (18%) were described. Late toxicity was present in two patients with grade 3 temporal lobe necrosis. (4) Conclusions: Hypofractionated proton therapy is showing encouraging preliminary results. However, to fully assess the efficacy of this therapeutic approach, future trials with adequate sample sizes and extended follow-ups are necessary.

Automated treatment planning for liver cancer stereotactic body radiotherapy

PURPOSE

To evaluate the quality of fully automated stereotactic body radiation therapy (SBRT) planning based on volumetric modulated arc therapy, which can reduce the reliance on historical plans and the experience of dosimetrists.

METHODS

Fully automated re-planning was performed on twenty liver cancer patients, automated plans based on automated SBRT planning (ASP) program and manual plans were conducted and compared. One patient was randomly selected and evaluate the repeatability of ASP, ten automated and ten manual SBRT plans were generated based on the same initial optimization objectives. Then, ten SBRT plans were generated for another selected randomly patient with different initial optimization objectives to assess the reproducibility. All plans were clinically evaluated in a double-blinded manner by five experienced radiation oncologists.

RESULTS

Fully automated plans provided similar planning target volume dose coverage and statistically better organ at risk sparing compared to the manual plans. Notably, automated plans achieved significant dose reduction in spinal cord, stomach, kidney, duodenum, and colon, with a median dose of D2% reduction ranging from 0.64 to 2.85 Gy. R50% and Dmean of ten rings for automated plans were significantly lower than those of manual plans. The average planning time for automated and manual plans was 59.8 ± 7.9 min vs. 127.1 ± 16.8 min (- 67.3 min).

CONCLUSION

Automated planning for SBRT, without relying on historical data, can generate comparable or even better plan quality for liver cancer compared with manual planning, along with better reproducibility, and less clinically planning time.

Influence and optimization strategy of the magnetic field in 1.5 T MR-linac liver stereotactic radiotherapy

OBJECTIVE

To compare intensity reduction plans for liver cancer with or without a magnetic field and optimize field and subfield numbers in the intensity-modulated radiotherapy (IMRT) plans designed for liver masses in different regions.

METHODS

This retrospective study included 62 patients who received radiotherapy for liver cancer at Shandong Cancer Hospital. Based on each patient's original individualized intensity-modulated plan (plan1.5 T), a magnetic field-free plan (plan0 T) and static intensity-modulated plan with four different optimization schemes were redesigned for each patient. The differences in dosimetric parameters among plans were compared.

RESULTS

In the absence of a magnetic field in the first quadrant, PTV Dmin increased (97.75 ± 17.55 vs. 100.96 ± 22.78)%, Dmax decreased (121.48 ± 29.68 vs. 119.06 ± 28.52)%, D98 increased (101.35 ± 7.42 vs. 109.35 ± 26.52)% and HI decreased (1.14 ± 0.14 vs. 1.05 ± 0.01). In the absence of a magnetic field in the second quadrant, PTV Dmin increased (84.33 ± 19.74 vs. 89.96 ± 21.23)%, Dmax decreased (105 ± 25.08 vs. 104.05 ± 24.86)%, and HI decreased (1.04 ± 0.25 vs. 0.99 ± 0.24). In the absence of a magnetic field in the third quadrant, PTV Dmax decreased (110.21 ± 2.22 vs. 102.31 ± 26)%, L-P V30 decreased (10.66 ± 9.19 vs. 5.81 ± 3.22)%, HI decreased (1.09 ± 0.02 vs. 0.98 ± 0.25), and PTV Dmin decreased (92.12 ± 4.92 vs. 89.1 ± 22.35)%. In the absence of a magnetic field in the fourth quadrant, PTV Dmin increased (89.78 ± 6.72 vs. 93.04 ± 4.86)%, HI decreased (1.09 ± 0.01 vs. 1.05 ± 0.01) and D98 increased (99.82 ± 0.82 vs. 100.54 ± 0.84)%. These were all significant differences. In designing plans for tumors in each liver region, a total number of subfields in the first area of 60, total subfields in the second zone of 80, and total subfields in the third and fourth zones of 60 or 80 can achieve the dose effect without a magnetic field.

CONCLUSION

In patients with liver cancer, the effect of a magnetic field on the target dose is more significant than that on doses to organs at risk. By controlling the max total number of subfields in different quadrants, the effect of the magnetic field can be greatly reduced or even eliminated.

Modern Stereotactic Radiotherapy for Brain Metastases from Lung Cancer: Current Trends and Future Perspectives Based on Integrated Translational Approaches

Brain metastases (BMs) represent the most frequent metastatic event in the course of lung cancer patients, occurring in approximately 50% of patients with non-small-cell lung cancer (NSCLC) and in up to 70% in patients with small-cell lung cancer (SCLC). Thus far, many advances have been made in the diagnostic and therapeutic procedures, allowing improvements in the prognosis of these patients. The modern approach relies on the integration of several factors, such as accurate histological and molecular profiling, comprehensive assessment of clinical parameters and precise definition of the extent of intracranial and extracranial disease involvement. The combination of these factors is pivotal to guide the multidisciplinary discussion and to offer the most appropriate treatment to these patients based on a personalized approach. Focal radiotherapy (RT), in all its modalities (radiosurgery (SRS), fractionated stereotactic radiotherapy (SRT), adjuvant stereotactic radiotherapy (aSRT)), is the cornerstone of BM management, either alone or in combination with surgery and systemic therapies. We review the modern therapeutic strategies available to treat lung cancer patients with brain involvement. This includes an accurate review of the different technical solutions which can be exploited to provide a "state-of-art" focal RT and also a detailed description of the systemic agents available as effective alternatives to SRS/SRT when a targetable molecular driver is present. In addition to the validated treatment options, we also discuss the future perspective for focal RT, based on emerging clinical reports (e.g., SRS for patients with many BMs from NSCLC or SRS for BMs from SCLC), together with a presentation of innovative and promising findings in translational research and the combination of novel targeted agents with SRS/SRT.

Stereotactic Body Radiation Therapy for Spine Metastases-Findings from an Australian Population-Based Study

Background: To evaluate the use of stereotactic body radiation therapy (SBRT) for spine metastases and the associated factors in Australia. Methods: The Victorian Radiotherapy Minimum Dataset, which captures all episodes of radiotherapy delivered in the state of Victoria, was accessed to evaluate the patterns and trends of SBRT for spine metastases. The primary outcome was SBRT use and associated factors. Results: There were 6244 patients who received 8861 courses of radiotherapy for spine metastases between 2012 and 2017. Of these, 277 (3%) courses were SBRT, which increased from 0.4% in 2012 to 5% in 2017 (P-trend < 0.001). There was a higher proportion of SBRT use in patients with prostate cancer (6%) and melanoma (4%) compared to other cancers (2-3%) (p < 0.001). Patients from the highest socioeconomic quintiles (5%) were more likely to be treated with SBRT compared to patients from the lowest socioeconomic quintiles (3%) (p < 0.001). There was a higher proportion of SBRT use in private radiotherapy centres (6%) compared to public radiotherapy centres (1%) (p < 0.001). No spine SBRT was delivered in regional centres. In multivariate analyses, the year of treatment, age, primary cancers and radiotherapy centres were independently associated with SBRT use. Conclusion: This is the first Australian population-based study quantifying the increasing use of spine SBRT; however, the overall use of spine SBRT remains low. We anticipate an ongoing increase in spine SBRT, as spine SBRT gradually becomes the standard-of-care treatment for painful spine metastases.