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Purpose: In the implementation of the use of EncompassTM partially open immobilization mask to perform SRS of multiple brain metastasis, the evaluation of patient's intrafraction motion (IM) is deemed convenient to verify that the margins applied to the GTV are able to ensure adequate dose coverage to each lesion. Methods: IM was determined by comparing the pre- and post-treatment CBCT images with respect to the simulation CT for a total of 23 fractions. The dosimetric impact on GTV coverage due to translational errors in patient positioning and rotational uncertainties of LINAC's performance was also evaluated. Results: The absolute magnitude of IM was less than 1 mm in all cases. The dosimetric difference on GTV coverage due to patient's IM was inferior to 5%. There was not found any significant correlation between the dosimetric impact of rotational uncertainties with the distance to the isocenter. Conclusions: The margins applied to the GTV are adequate when using EncompassTM immobilization device. [ABSTRACT FROM AUTHOR]

Purpose: Optimal timing of SRS after surgical resection of brain metastases (BMs) remains debated but is generally advocated to occur within 4 weeks of surgery to account for cavity remodeling. Our study assesses this recommendation by examining cavity dynamics and any downstream effects on outcome. Methods: Post-operative MRIs were used to compare target lesion volumes to target volume at time of SRS. Spearman's analysis identified a relationship between the time to SRS (ttSRS) and target remodeling. The Mann-Whitney-U test compared median remodeling between groups receiving standard (=4 weeks) and late (>4 weeks) adjuvant SRS. Kaplan Meier functions estimated probabilities of local recurrence (LR) and survival (OS). A Cox proportional hazards model (CPH) identified predictors of OS, LR, and leptomeningeal disease (LMD). Results: Median ttSRS was 32 days (3-72). A positive correlation exists when comparing ttSRS to reduction in cavity volume (0-10 weeks; p = 0.01) with no difference in median cavity remodeling between standard and late SRS groups. OS and LR rates were respectively 53.3% and 70.2% at 12 months with no difference in OS (p = 0.16) or LR (p = 0.54) between standard and late SRS groups. Subtotal resection predicted LMD (HR: 6.37; p = 0.03). No grade 3 or higher toxicity was seen in follow-up. Conclusions: Resection cavities may continue to shrink well after resection. There is no significant difference in OS or LR based on ttSRS, however, treatment factors such as the extent of resection may account for outcomes such as LMD. [ABSTRACT FROM AUTHOR]

Purpose/Objective(s): Accurate delineation of target is key to any successful radiosurgery. C-arm Dyna CT/3DCT angiography (3DCTA) has the potential of improving the accuracy of nidus delineation in intracranial arteriovenous malformations (AVM) due to high temporo-spatial resolution of vessel architecture. Here, we present a comparison of nidus delineation and dosimetric parameters between digital 3DCTA and MRI. Materials/Methods: Ten consecutive patients treated for intracranial AVMs were included in this study. All patients underwent MRI/MRA, and 3DCTA and all images were co-registered. AVM were delineated using 3DCTA (GTV3DCTA) and contrast enhanced MRI/MRA (GTVMRI). Hausdorff distance (HD) matrices and dice similarity coefficient (DSC) matrices were analysed. Stereotactic radiosurgery plans were developed for both the volumes for all patients and statistical analysis were performed with T-test. Results: Mean volumes of GTV3DCTA and GTVMRI were 1.771 cc (SD 1.794cc, range 0.124-4.191cc) and 2.183cc (SD 2.16cc, range 0.221-6.133cc), respectively. Significant deviation (p=0.018) was found when taking GTVMRI as a primary and comparing it to GTV3DCTA (MD=0.723cc±0.816cc). Similar result was observed with GTV3DCTA as primary and GTVMRI as secondary (MD=0.188cc, SD=0.193cc, p=0.024). Maximum HD was in the range of 1.71 to 7.44mm (mean=4.27mm, SD=1.56). For GTV3DCTA based plans, significant deviation was found between GTVMRI and GTV3DCTA in dose coverage and the mean difference was 22.17% (SD 16.73). In GTVMRI based plans, the mean CIRTOG deteriorated from 1.33 to 2.18 for GTVMRI and GTV3DCTA, respectively. Significant deviation was found in CIRTOG (0.005) and mean deviation was 0.86(SD=0.72) when comparing GTVMRI and GTV3DCTA. Highly significant (p=0.002) deviation was found in CIPaddick between GTVMRI and GTV3DCTA for GTVMRI based plans with mean difference of 0.26(SD=0.4, for GTVMRI=0.3, GTV3DCTA=0.46). Conclusion: Nidus volume was significantly altered with the use of 3DCTA compared to that of MRA/MRI images. Multimodality imaging is crucial for accurate target delineation, and successful radiosurgical obliteration of nidus. [ABSTRACT FROM AUTHOR]

Objectives: Stereotactic radiosurgery (SRS) is part of the multimodality treatment for patients with cancer. The objective of this study is to determine factors which influence overall survival (OS) of Filipino patients who underwent SRS for metastatic tumors of the spine. Methods: This is a retrospective analysis of a cohort of Filipino patients treated with spine SRS for metastatic tumors in a single institution. Putative predictors were determined by the institution's spine SRS team and described in the cohort. A Cox proportional hazards regression model was utilized to construct a model based on the predictors determined by the institution's spine SRS team. Results: A total of 51 consecutive patients with 68 spine metastases were treated with SRS at our institution. The median OS was 13.1 months (95% CI of 7.1 to 19.1). On multivariate analysis, significant predictors that are associated with OS were visceral tumor origin (adjusted HR: 3.08, 95% CI of 1.24 to 7.64, p = 0.015) and cardiovascular disease (adjusted HR: 2.50, 95% CI of 1.04 to 5.94, p = 0.039) with dose and number of fractions as co-variates [Model Wald X2 (5, N = 51) = 11.11 (p = 0.049)]. Conclusion: The presence of visceral tumor origins and cardiovascular disease are independent factors that are associated with lower overall survival in Filipino patients with spine metastasis treated with SRS. [ABSTRACT FROM AUTHOR]

In Gamma Knife (GK) radiosurgery, dose rate decreases during the life cycle of its radiation source, extending treatment times. Prolonged treatments influence the amount of sublethal radiation injury that is repaired during exposure, and is associated with decreased biologically-equivalent dose (BED). We assessed the impact of treatment times on clinical outcomes following GK of the trigeminal nerve - a rare clinical model to isolate the effects of treatment times. This is a retrospective analysis of 192 patients with facial pain treated across three source exchanges. All patients were treated to 80 Gy with a single isocenter. Treatment time was analyzed in terms of patient anatomy-specific dose rate, as well as BED calculated from individual patient beam-on times. An outcome tool measuring pain in three distinct domains (pain intensity, interference with general and oro-facial activities of daily living), was administered before and after intervention. Multivariate linear regression was performed with dose rate/BED, brainstem dose, sex, age, diagnosis, and prior intervention as predictors. BED was an independent predictor of the degree of improvement in all three dimensions of pain severity. A decrease in dose rate by 1.5 Gy/min corresponded to 31.8% less improvement in the overall severity of pain. Post-radiosurgery incidence of facial numbness was increased for BEDs in the highest quartile. Treatment time is an independent predictor of pain outcomes, suggesting that prescription dose should be customized to ensure iso-effective treatments, while accounting for the possible increase in adverse effects at the highest BEDs. [ABSTRACT FROM AUTHOR]

Objectives: Patients undergoing stereotactic radiosurgery (SRS) for brain metastases require additional radiation for relapse. Our objective is to determine the factors associated with salvage SRS versus whole brain radiation therapy (WBRT) for salvage of first intracranial failure (ICF) after upfront SRS. Methods: We identified a cohort of 110 patients with brain metastases treated with SRS in the definitive or postoperative setting followed by subsequent salvage WBRT or SRS at least one month after initial SRS. Clinical and demographic characteristics were retrospectively recorded. Results: 78 Patients received SRS and 32 patients received WBRT at the time of first ICF. On multivariate analysis (MVA) factors associated with decreased use of salvage SRS were male gender (p=0.044) and local progression (p<0.001). Conclusions: Local progression and male gender were the strongest factors associated with selection of salvage WBRT. Possible etiologies of this difference could be provider or patient driven, but warrant further exploration. [ABSTRACT FROM AUTHOR]

Background: While immunotherapy has been shown to improve survival and decrease neurologic death in patients with brain metastases, it remains unclear whether this improvement is due to prevention of new metastasis to the brain. Methods: We performed a retrospective review of patients presenting with brain metastases simultaneously with the first diagnosis of metastatic disease and were treated with upfront immunotherapy as part of their treatment regimen and stereotactic radiosurgery (SRS) to the brain metastases. We compared this cohort with a historical control population (prior to the immunotherapy era) who were treated with pre-immunotherapy standard of care systemic therapy and with SRS to the brain metastases. Results: Median overall survival time was improved in the patients receiving upfront immunotherapy compared to the historical cohort (48 months vs 8.4 months, p=0.001). Median time to distant brain failure was statistically equivalent (p=0.3) between the upfront immunotherapy cohort and historical control cohort (10.3 vs 12.6 months). Brain metastasis velocity was lower in the upfront immunotherapy cohort (median 3.72 metastases per year) than in the historical controls (median 9.48 metastases per year, p=0.001). Cumulative incidence of neurologic death at one year was 12% in the upfront immunotherapy cohort and 28% in the historical control cohort (p=0.1). Conclusion: Upfront immunotherapy appears to improve overall survival and decrease BMV compared to historical controls. While these data remain to be validated, they suggest that brain metastasis patients may benefit from concurrent immunotherapy with SRS. [ABSTRACT FROM AUTHOR]

The aim of this work is to verify the potential use of GAFchromic™ EBT3 and FILMQA™ pro software for patient specific quality assurance (QA) for stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT) treatment plans in clinical routine use. In particular, encephalic, pulmonary and lymph node treatments plans were selected for this study. The agreement between the calculated and measured dose distributions were evaluated in terms of ɣ index with 3%3mm, 2%2mm, 1.5%1.5mm and 3%1.5mm criteria. The obtained results were then compared to the routine pretreatment verification method which uses electronic portal imaging device (EPID) and EPIQA analysis software. EBT3-FilmQA method results show a mean ɣ index passing rate >95% with 2%1.5mm analysis criteria and an improvement of about 7% compared with EPID-EPIQA method results. [ABSTRACT FROM AUTHOR]

Purpose: Competing radiosurgery plans are compared based on their conformity and gradient of dose distribution to the target volume (TV). Most widely used quality metrics such as new conformity index (NCI) and gradient index (GI) are known to have strong volume dependency on the TV of interest. A simple quality measure without the volume dependency is presented for evaluating stereotactic radiosurgery plans, expressed in distance dimension compared to the unit-less volume ratio used in NCI and GI. Methods and Materials: The conformity distance measure (CDM) is defined as the effective radius of the union volume subtracted by that of the intersection volume, where volume operations are on TV and prescription isodose volume (PIV). Gradient distance measure (GDM) is defined as the effective radius of 50% PIV (low dose volume of the plan) subtracted by that of corresponding ideal low dose volume (iLDV). Volume independency and consistent sensitivity of CDM and GDM on PIV displacement and dose spillage are analyzed using a simple two-sphere model. 2429 cases of Gamma Knife and 76 cases of Linac based radiosurgery plans for brain metastasis were retrospectively studied to demonstrate volume independency of the new measures and their implication on target coverage. Results: The sensitivity of NCI on PIV displacement and dose spillage was inversely proportional to the effective radius of the target volume, while the sensitivity of CDM on target motion and dose spillage was constant regardless the target volume. The iLDV for 50% PIV was approximately 2.4 times of PIV based on previous Linac based radiosurgery/IMRT/VMAT plans and single shot analysis from Gamma Knife (GK), ICON. Although NCI ranged from 1 to 14.7 for GK plans and from 1.2 to 20.8 for VMAT plans showing strong volume dependency, CDM showed negligible volume dependency of less than 2.1 mm for more than 90% cases and peak frequency was at 0.8 mm. CDM was correlated well with target coverage as a function of PIV displacement regardless of target volume. Target coverage, V100, was larger than 95% when PIV displacement is less than CDM. Conclusion: The new conformity and gradient measure, CDM and GDM are proposed in this paper. The new measures are volume independent which is preferred for reliable evaluation of the radiosurgery plan quality over wide range of radiosurgery targets. As represented by distance dimension similar to PTV margin, the new measures may be more adequate for image guided radiosurgery applications. [ABSTRACT FROM AUTHOR]

Two automated treatment planning techniques were evaluated for multiple brain metastases using a single isocenter. One technique is knowledge-based planning (KBP) using a stereotactic radiosurgery (SRS) model in Eclipse treatment planning system (TPS); and the other is the Multiple Brain Mets (MBM) SRS technique in Brainlab Elements TPS. Eighteen plans each with 3-10 lesions were used for the study. Plan evaluation metrics included the planning target volume (PTV) coverage, conformity index (CI), total monitor units (MUs), plan optimization time, brain V12Gy, V8Gy, and V5Gy. Both the KBP and MBM planning techniques produced comparable plans to the manually generated clinical plans in terms of PTV coverage and CI. For irregularly shaped lesions, the KBP plans provided more conformal dose distribution to the PTV than the MBM plans. The KBP plans took significantly longer time to plan but have fewer MUs than the MBM plans. The MBM plans spared normal brain tissues better than the KBP plans in terms of V5Gy. [ABSTRACT FROM AUTHOR]

Purpose: The epidural space is a frequent site of cancer recurrence after spine stereotactic radiosurgery (SSRS). This may be due to microscopic disease in the epidural space which is underdosed to obey strict spinal cord dose constraints. We hypothesized that the epidural space could be purposefully irradiated to prescription dose levels, potentially reducing the risk of recurrence in the epidural space without increasing toxicity. Methods and materials: SSRS clinical treatment plans with spinal cord contours, spinal planning target volumes (PTVspine), and delivered dose distributions were retrospectively identified. An epidural space PTV (PTVepidural) was contoured to avoid the spinal cord and focus on regions near the PTVspine. Clinical plan constraints included PTVspine constraints (D95% and D5%, based on prescription dose) and spinal cord constraints (Dmax < 1300 cGy, D10% < 1000 cGy). Plans were revised with three prescriptions of 1800, 2000 and 2400 cGy in two sets, with one set of revisions (subplemented plans) designed to additionally target the PTVepidural by optimizing PTVepidural D95% in addition to meeting every clinical plan constraint. Clinical and revised plans were compared according to their PTVepidural DVH distributions, and D95% distributions. Results: Seventeen SSRS plans meeting the above criteria were identified. Supplemented plans had higher doses to the epidural low-dose regions at all prescription levels. Epidural PTV D95% values for the supplemented plans were all statistically significantly different from the values of the base plans (p < 10-4). The epidural PTV D95% increases depended on the initial prescription, increasing from 11.52 to 16.90 Gy, 12.23 to 18.85 Gy, and 13.87 to 19.54 Gy for target prescriptions of 1800, 2000 and 2400 cGy, respectively. Conclusion: Purposefully targeting the epidural space in SSRS may increase control in the epidural space without significantly increasing the risk of spinal cord toxicity. A clinical trial of this approach should be considered. [ABSTRACT FROM AUTHOR]

Objectives: To perform a systematic review and meta-analysis of outcomes for patients with locally recurrent brain metastases treated with a repeat course of stereotactic radiosurgery (rSRS). Method: Primary outcomes were 1-year local control(LC) and radionecrosis (RN). Secondary outcomes were 1-year overall survival (OS) and 1-year distant brain control (DBC). Weighted random effects meta-analyses utilizing the DerSimonian and Laird methods were conducted to characterize summary effect sizes. Mixed effects regression models were utilized to analyze potential correlations between prognostic factors and outcomes. Results: In total, 347 patients with 462 brain metastases treated with rSRS were included. Estimated 1-year LC, OS, and DBC rates were 69.0% (95% CI: 61.0-77.0%), 49.7% (95% CI: 28.9-70.6%), and 41.6% (95% CI: 33.0-50.4%), respectively. The estimated RN rate was 16.1% (95% CI: 6.3-25.9%). Every 1 Gy increase in prescription dose was estimated to result in roughly 5% increase in 1-year LC (p = 0.14). Conclusions: rSRS was well-tolerated with reasonable 1-year LC and OS. Dose escalation may result in improved LC. [ABSTRACT FROM AUTHOR]

Purpose: To investigate whether there is a volume threshold in target volume of brain metastases below which a small cone size and sharp penumbra in Gamma Knife (GK) may provide improved plan quality when compared to Volumetric Modulated Arc Therapy (VMAT)-based stereotactic radiosurgery (SRS). Methods: For patients treated on GK SRS for brain metastases in 2018-2019 in our institution, 121 patients with two and three targets were identified. Twenty-six patients with two or three brain metastases (total of 76 lesions) were selected for this study. Two VMAT plans, SmartArc (Pinnacle) and HyperArc (Eclipse), were generated retrospectively for each patient. Plan quality was evaluated based on RTOG conformity index (CI), Paddick gradient index (GI), normal tissue (NT) V12Gy and V4.5Gy. By using the receiver operating characteristic (ROC) curve for both VMAT plans (SmartArc and HyperArc) and metrics of RTOG CI and NT V12Gy, we compared GK plans to SmartArc and HyperArc plans separately to determine the threshold volume. Results: For SmartArc plans, both ROC curve analyses showed a threshold volume of 0.4 cc for both CI and NT V12Gy. For HyperArc plans, the threshold volumes were 0.2 cc for the CI and 0.5 cc for NT V12Gy. GK plans produced improved dose distribution compared to VMAT for targets =0.4 cc, but HyperArc was found to have competing results with GK in terms of CI and NT V12Gy. For targets > 0.4 cc, both SmartArc and HyperArc showed better plan quality when compared to the GK plans. Conclusions: Target volumes =0.4 cc may require a small cone size and sharp penumbra in GK while for target volumes >0.4 cc, VMAT-based SRS can provide improved overall plan quality and faster treatment delivery. [ABSTRACT FROM AUTHOR]

The purpose of this study is to compare patient-specific quality assurance (PSQA) results between two dimensional (2D) diode (SRS MapCHECK®) and 3D diode (ArcCHECK®) arrays. Twenty-eight intracranial stereotactic radiosurgery (SRS) and 26 lung stereotactic body radiation therapy (SBRT) clinical plans with a single lesion were selected and categorized into 4 groups: 20 SRS dynamic conformal arc therapy (DCAT) plans (Group A), 8 SRS volumetric modulated arc therapy (VMAT) plans (Group B), 6 SBRT DCAT plans (Group C) and 20 SBRT VMAT plans (Group D). An individual field of each plan was delivered on SRS MapCHECK and ArcCHECK and QA analysis was performed using 4 gamma criteria of dose difference/distance-to-agreement of 3%/3 mm, 3%/2 mm, 2%/2 mm and 2%/1 mm. Statistical analysis was performed to compare PSQA results between the 2 QA devices. For all 4 groups and all 4 gamma criteria, average gamma passing rates were higher with SRS MapCHECK. [ABSTRACT FROM AUTHOR]

Purpose/objective: Linear accelerator (LINAC) based stereotactic radiosurgery (SRS) for arteriovenous malformations (AVMs) is delivered with cone or multileaf collimators (MLCs), and favorable dosimetry is associated with reduced radionecrosis in normal brain tissue. This study aims to determine whether cones or MLCs has better dosimetric characteristics, to predict differences in toxicity. Methods: All patients treated for AVMs using LINAC SRS from 2003-2017 were examined retrospectively. Demographic data, volumes of normal tissue exposed to 12Gy (V12Gy[cc]) and 4Gy (V4Gy[cc]), maximal dose, and dose gradient were analyzed. Univariate and multivariate analyses were used to evaluate relationships between collimator type, dosimetric parameters, and toxicity. Propensity score matching was used to adjust for AVM size. Results: Compared to MLC, cones were independently associated with reduced V12Gy[cc] after propensity score matching (p=0.008) and reduced neurotoxicity (p=0.016). Higher V12Gy[cc] (p=0.0008) and V4Gy[cc] (p=0.002) were associated with increased neurotoxicity. Conclusions: Treating AVMs with cone-based SRS over MLC-based SRS may improve dosimetry and reduce toxicities. [ABSTRACT FROM AUTHOR]

Treatments for melanoma have significantly advanced with the approval of targeted treatments against the BRAF/MEK pathway and immunotherapy in the form of checkpoint inhibitors. Studies have shown the effectiveness of these treatments against brain metastases. However, the optimum treatment strategy utilising CNS-directed treatments such as stereotactic radiosurgery (SRS) and neurosurgical resection is less clear. Over six years, 70 patients with metastatic melanoma were treated for brain metastases at a tertiary treatment centre. The median overall survival (OS) for all patients was 10.2 months. 51 patients received localised treatment; 7 resection (median OS 10 months), 11 resection and SRS (median OS 17.3 months) and 33 SRS alone (median OS 17.4 months). For patients treated with SRS those who had <2 cm3 treated had a better median OS (20.5 months) compared to those who had >2 cm3 treated (12 months). 69 Patients received systemic treatment. The median OS of patients who did not have CNS-directed treatment was poor (median OS 1.2 months). Patients treated with first line dual immunotherapy had the best median OS (26.7 months), compared to anti-PD-1 (14.1 months), ipilimumab (14.3 months) and kinase inhibitors (10.9 months). Despite advancements in treatment, the development of brain metastases in melanoma is associated with worse outcomes. A combination of CNS-directed and systemic treatment is important to improve survival. Dual immunotherapy appears to be the most effective systemic treatment and the use of SRS improved outcomes. As metastatic melanoma treatments evolve there need to be an ongoing focus to ensure these strategies adequately treat intracranial disease. [ABSTRACT FROM AUTHOR]

Background: In the context of the largest democracy of the world (India) with wide variations in the demographic and socio-economic parameters, there is an immense need for a wide reach of advanced radiotherapy facilities. We aim to study the patterns and socio-economic aspects of stereotactic radiosurgery in India. Methods: The study is based on an online survey consisting of 20 questions. The participants were all radiation oncology professionals in India. Results: An online questionnaire was prepared and sent to nearly 400 radiation oncologists across the country and we received responses from 78 members. The majority of the participants were practicing Stereotactic radiotherapy. 76% of the participants were located in urban regions. All centers are equipped with Linear accelerators. 89% of centers have facilities to practice SRS. 65% of them have less than 3 years of experience. There were wide variations in the cost of treatment with an average cost of between 1-3lakhs INR (1350-4100$). The majority of people with medical insurance reside in urban locations and those patients who go to small and medium private hospitals and government colleges have state-run health schemes. Participants gave various suggestions for the wider accessibility of SRS facilities across the nation. Conclusions: Initiatives are to be taken at multiple levels to make stereotactic radiotherapy easily and widely available across the country. [ABSTRACT FROM AUTHOR]

The accuracy of stereotactic radiosurgery (SRS) to multiple metastases with a single-isocenter using high definition dynamic radiosurgery (HDRS) was evaluated across institutions. An SRS plan was delivered at six HDRS-capable institutions to an anthropomorphic phantom consisting of point, film, and 3D-gel dosimeters. Direct dose comparison and gamma analysis were used to evaluate the accuracy. Point measurements averaged across institutions were within 1.2±0.5%. The average gamma passing rate in the film was 96.6±2.2% (3%/2 mm). For targets within 4 cm of the isocenter, the 3D dosimetric gel gamma passing rate averaged across institutions was >90% (3%/2 mm). The targeting accuracy of high definition dynamic radiosurgery assessed by geometrical offset of the center of dose distributions across multiple institutions in this study was within 1 mm for targets within 4 cm of isocenter. Across variations in clinical practice, comparable dosimetry and localization is possible with this treatment planning and delivery technique. [ABSTRACT FROM AUTHOR]

Patient selection For boost treatments: Patients undergoing a lumpectomy as part of breast-conserving therapy can be eligible for a GammaPod boost treatment. This workflow consists of patient selection, daily quality assurance (QA), breast cup fitting, CT imaging, treatment planning, and treatment. [Extracted from the article]

Introduction: Single-fraction stereotactic radiosurgery (SF-SRS) is typically used to provide local control of brain metastases. Recently, hypofractionated stereotactic radiotherapy (HF-SRT) has been utilized for large brain metastases. Data comparing these two modalities are limited for brain metastases ≤3 cm. Methods: Patients with brain metastases receiving linear accelerator-based SF-SRS or HF-SRT were identified at three institutions. Local progression-free survival (LPFS), intracranial progression-free survival (ICPFS), overall survival (OS), and radionecrosis-free survival (RNFS) were determined from time of treatment. Results: 108 patients (76 intact, 32 resected) with 184 brain metastases (142 intact, 42 resected) were included. There were no significant differences between SF-SRS and HF-SRT for intact metastases in 1-year LPFS (62.8% vs. 58.5%, p=0.631), ICPFS (56.9% vs. 55.3%, p=0.300), and OS (71.6% vs. 70.6%, p=0.096), or for resected metastases in 1-year LPFS (67.3% vs. 57.8%, p=0.288), ICPFS (64.8% vs. 57%, p=0.291), and OS (64.8% vs. 66.1%, p=0.603). There were also no significant differences in 1-year RNFS between SF-SRS and HF-SRT (92% vs. 92%, p=0.325). Conclusions: There were no significant differences in LPFS, ICPFS, OS, and RNFS between SF-SRS and HF-SRT for brain metastases ≤3 cm suggesting SF-SRS may be preferred due to similar outcomes and reduced number of fractions. [ABSTRACT FROM AUTHOR]

Superficial siderosis (SS) of the brain results from a chronic iron toxicity due to repeated microscopic leakage of blood products into the subarachnoid space. We report on Gamma Knife Radiosurgery (GKRS) associated worsening of superficial siderosis in a patient with skull-base tumor. A 73 year-old male patient presented with clumsiness and gait ataxia and was diagnosed with foramen magnum meningioma. He was also noted to have superficial siderosis involving the mainly the infratentorial compartment. After a thorough evaluation of craniospinal axis, no other cause of bleeding was identified. Patient was treated with the GKRS. After GKRS, there was an initial radiological and clinical worsening of SS starting at 6 months and peaking at 2 years. The disease stabilized and showed mild reduction at 3 years. GKRS lead to an initial progression of superficial siderosis. However, over a longer period, tumor control and improvement of the siderosis was observed. [ABSTRACT FROM AUTHOR]

AAPM TG-218 provides recommendations for standard IMRT pre-treatment QA without giving specifics for stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT). In light of this, our purpose is to report our experience with applying TG-218 recommendations to a large multicenter clinical SRS and SBRT program for a range of diverse clinical pre-treatment QA systems. Pre-treatment QA systems included Delta4 (Scandidos), Portal Dosimetry (Varian Medical Systems), ArcCHECK (SunNuclear), and SRS MapCHECK (SunNuclear). Plans were stratified by technique for each QA system, and included intracranial and extracranial IMRT and VMAT (total QA cases n=275). Gamma analysis was re-analyzed with spatial/dose criteria combinations ranging from 1 to 3 mm and 1% to 4%, and action and tolerance limits were calculated per plan type and compared to the "universal" TG-218 action limit of 90%. The analysis indicated that spatial tolerance criteria could be tightened to 1 mm while still maintaining an in-control QA process for all QA systems evaluated. [ABSTRACT FROM AUTHOR]

Introduction: Two-staged stereotactic radiosurgery (SRS) has been shown as an effective treatment for brain metastases that are too large for single fraction SRS. Methods: Patients with large brain metastases (>4 cm³) treated with two-staged SRS from January 2017 to December 2019 at our institution were retrospectively identified. Results: There were 23 brain metastases treated. The normal brain volume receiving equivalent 12Gy-in-single-fraction was defined as V12E. The V12E for original single-fraction GKS plan (mean of 41.4 cm³, range 5.6-146.1 cm³) was significantly higher compared to that of the second stage (mean of 23.7 cm³, range 2.8-92.7 cm³). The median tumor volume measured at the second stage (4.30 cm³) was reduced by an average of 52.2% compared to the first stage (9.58 cm³). Three patients (27.3%) showed local tumor progression in 4 tumors (20%). The median time to progression was 152 days. Conclusions: Two-staged SRS is an effective treatment technique for large brain metastasis that results in significant reduction of tumor volume at the second stage SRS. Optimal treatment dose has not yet been defined. [ABSTRACT FROM AUTHOR]

Purpose: A major factor in dose-fractionation selection for intracranial metastases in stereotactic radiosurgery (SRS) is the size of the target lesion and consequently the dose-volume to the surrounding normal brain tissue (NTV), as this has been correlated with brain radiation necrosis (RN). This study outlines the development and validation of a predictive model that can estimate the NTV for a range of dose-fractionation schemes based on target diameter from a patient's MRI. Methods: Data from a cohort of historical SRS clinical treatment plans were used to extract three key input parameters for the model - conformity index, gradient index, and a scaling factor - which were then defined as a function of target volume. The relationship between the measured tumour diameter and the NTV was established by approximating the target to a spherical volume covered by the prescription dose. A scaling factor (λNTV) describes the non-linear fall-off of dose beyond the target. This was then used to provide a first-order approximation of the resulting NTV. The predictive model was retrospectively validated using linear regression against actual NTV values from 39 historical SRS plans which were independent to the derivation process. The model was validated for both three-dimensional (3D) target diameter and axial-only two-dimensional (2D) estimates of target diameter values. Results: The prediction model directly relates lesion diameter to NTV volume (cc) and thus RN risk for a given dose-fractionation. The predicted NTV (cc) for both 3D- and 2D-based volume estimates could statistically significantly predict the actual NTV (cc): R²=0.942 (p<.0005) for 3D-based estimate, and R²=0.911 (p=<.0005) for axial-only 2D-based estimate. Conclusion: This knowledge-based method for NTV prediction in intracranial SRS provides the clinician with a decision support tool to appropriately select dose-fractionation prior to treatment planning. [ABSTRACT FROM AUTHOR]

Objectives: Brain metastases are a rare finding in patients with primary gynecologic malignancies having a poor outcome despite treatment. We sought to use the National Cancer Database (NCDB) to characterize the incidence of brain metastases and types of treatment administered. Methods: We queried the NCDB from 2010-16 for patients with endometrial, cervical, and ovarian primaries with brain metastases at diagnosis treated with radiation--whole brain radiation (WBRT) or stereotactic radiosurgery (SRS). We tabulated baseline characteristics and performed a multivariable logistic regression to identify predictors of SRS. Multivariable Cox regression was used to identify predictors of death. Propensity matching was done to account for indication bias. Results: We identified 765 patients meeting above criteria, representing <1% of patients. Of patients with brain metastases, 287 received radiation to the brain. The median age was 60 (40-90). The majority of patients (80%) received WBRT. On multivariable logistic regression the only predictor of SRS was receipt of chemotherapy. Median follow up was 4.9 months. The overall survival for the entire cohort was 5.2 months. On Cox regression predictors of improved survival were receipt of chemotherapy, no extracranial disease, and SRS. After propensity matching, median survival was 8.3 months compared to 6.3 months in favor of SRS. Conclusions: This study represents the largest series to date of patients with brain metastases from gynecologic malignancies, confirming an incidence of <1% and overall poor prognosis. Radiation remains a viable treatment option. [ABSTRACT FROM AUTHOR]

Introduction: Patients with small cell lung cancer (SCLC) brain metastasis (BM) typically receive whole brain radiotherapy (WBRT) as data regarding upfront radiosurgery (SRS) in this setting are sparse. Methods: Patients receiving SRS for SCLC BM without prior brain radiation were identified at three U.S. institutions. Overall survival (OS), freedom from intracranial progression (FFIP), freedom from WBRT (FFWBRT), and freedom from neurologic death (FFND) were determined from time of SRS. Results: Thirty-three patients were included with a median of 2 BM (IQR 1-6). Median OS and FFIP were 6.7 and 5.8 months, respectively. Median FFIP for patients with =2 versus >2 BM was 7.1 versus 3.6 months, p=0.0303. Eight patients received salvage WBRT and the 6-month FFWBRT and FFND were 87.8%. and 90.1%, respectively. Conclusions: Most SCLC patients with BM who received upfront SRS avoided WBRT and neurologic death, suggesting that SRS may be an option in select patients. [ABSTRACT FROM AUTHOR]

Objective: The COVID-19 pandemic necessitated drastic and rapid changes throughout the field of radiation oncology, some of which were unique to the discipline of radiosurgery. Guidelines called for reduced frame use and reducing the number of fractions. Our institution implemented these guidelines, and herein we show the resultant effect on patient treatments on our Gamma Knife Icon program. Methods: In early March 2020 we rapidly implemented suggested changes according to ASTRO and other consensus guidelines as they relate to stereotactic radiosurgery in the COVID-19 era. We reviewed the GK Icon schedule at our institution between January 01 and April 30, 2020. We documented age, condition treated, technique (frame vs. mask), and number of fractions. We then tabulated and graphed the number of patients, framed cases, and fractions delivered. Results: Seventy-seven patients were treated on the GK Icon over that period, for a total of 231 fractions. The number of unique patients varied from 18 (April) to 22 (January). Of the 77 patients only 5 were treated using a frame. The number of fractions per month decreased significantly over time, from 70 in January to 36 in April. Likewise, the percentage of single fraction cases increased from 4.5% per month in January to 67% in April. Conclusions: The results presented here show that it is possible to quickly and efficiently change work flows to allow for reduced fractionation and frame use in the time of a global pandemic. Multidisciplinary cooperation and ongoing communication are integral to the success of such programs. [ABSTRACT FROM AUTHOR]

Stereotactic radiosurgery (SRS) is used as a noninvasive treatment option for patients with trigeminal neuralgia (TN), but the effect of obesity on pain relief post SRS, if any, is unknown. The primary goal of our study was to evaluate the association between obesity and response to SRS in patients with TN. We conducted an IRB-approved retrospective review of patients treated with SRS for TN between 2010 and 2017. Barrow Neurologic Institute (BNI) Score was assigned pre-and post-SRS to quantify pain level. Thirty-two patients (65% female) between the ages of 24 and 96 were studied with a median follow-up time of 11 months. Patients with BMI >25 were significantly less likely to have improvement in their symptoms with SRS (p = 0.005). Elevated BMI may be associated with worsened response to SRS in the treatment of TN. [ABSTRACT FROM AUTHOR]

A 52 year-old gentleman with metastatic pheochromocytoma received single fraction spine stereotactic radiosurgery (SSRS) to an isolated L3 metastasis. Two years later, he developed widespread osseous metastatic disease involving nearly every vertebral body level with the striking exception of the treated L3 vertebrae. The "seed and soil" hypothesis of metastatic dissemination was developed over a century ago and states that tumors cells (the "seed") preferentially grow in select host tissue microenvironments (the "soil"). The high-dose radiation delivered by SSRS may have altered the microenvironment "soil" of the treated L3 vertebrae, rendering it inhospitable to the growth of future metastases. With emerging evidence in support of high-dose stereotactic radiation for oligometastatic disease, there will likely be increasing opportunity to observe and understand treatment changes in the tissue microenvironment and how it relates to the potential for metastatic seeding. [ABSTRACT FROM AUTHOR]

Stereotactic body radiation therapy (SBRT) and stereotactic radiosurgery have become widely used in both palliative and curative treatments for variety of primary and secondary malignancies. Although the indications and use of stereotactic techniques have increased substantially in the past decades, there been no studies to date analyzing public interest in these techniques. Using Google Trends (Google LLC, Mountain View, CA), four search terms ("SBRT," "stereotactic radiosurgery," "Gamma Knife" and "Cyberknife") were analyzed in the U.S. from January 2004 to June 2019. Each term was assigned a relative interest score based on frequency of searches. "SBRT" is becoming an increasingly popular search term, reaching peak interest in October 2018. Conversely, "stereotactic radiosurgery" and "Gamma Knife" radiosurgery initially had high interest, before declining over the past decade. "Cyberknife" was most popular in the mid-2000s but decreased steadily since that time. These trends were subsequently compared against PubMed publication data over the same time. [ABSTRACT FROM AUTHOR]

Radiation-associated malignancy and malignant transformation are risks associated with stereotactic radiosurgery (SRS); however, incidence is uncertain. The purpose of our study is to present the rate of radiation-associated malignancy and malignant transformation at our institution. After IRB approval, we undertook a retrospective cohort study evaluating patients treated with Gamma Knife® or linac-based SRS between 1990 and 2014 for benign CNS pathology with at least 5 years of clinical follow-up. Risk of transformation was calculated using the Kaplan-Meier method. A total of 273 patients met selection criteria. Median clinical follow-up after SRS was 11 years (range 5-27). Over 3,216 patient-years following SRS, we found zero cases of radiation-associated malignancy and two cases of radiation-associated malignant transformation for a crude rate of 0.73% or case rate of 0.62 per 1,000 patient-years. The Kaplan-Meier risk of malignant transformation at 5, 10, and 15 years was 0.4% (95% CI 0.05% - 2.6%). These data support the continued use of SRS for benign intracranial pathology without significant concern for secondary malignancy. [ABSTRACT FROM AUTHOR]

Purpose/Objectives: The Gamma-Knife radiosurgery (GKRS) (Elekta AB, Stockholm) platform delivers highly conformal and precise radiation; however, intracranial displacement during treatment allows for the potential of a marginal target-miss. Frameless (mask-based) GKRS using the Gamma Knife Icon system monitors nasal tip motion as a surrogate for intracranial motion by tracking an infrared marker using a high-definition motion management (HDMM) system. To date, there is limited data available regarding the incidence and severity of motion and factors that impact intrafraction motion when treating with frameless GKRS. Materials/Methods: A retrospective study was performed to evaluate patients with brain tumors who were treated with frameless GKRS using the Gamma Knife Icon between May and December 2018. All patients underwent mask-based immobilization using a thermoplastic mask. Data on patient demographics, mask type, use of bite block, and number of treatments received, use of anxiolytics, treatment time, and whether a physics clearance check was performed prior to treatment were collected. For each treatment session, average displacement (mm), maximum displacement (mm) and total treatment time (min) were recorded and logistic regression analyses were performed. Results: Data was collected for 89 consecutive treatments (38 patients). Of these, an anxiolytic was used in 61 treatments and a physics clearance check was performed for 45 treatments. The median average and maximum displacement was 0.60 mm and 1.22 mm, respectively. An average displacement greater than 0.60 mm was seen with Eastern Cooperative Oncology Group performance status (ECOG) > 1, male gender, and malignant tumors (p < 0.05). Anxiolytic use prior to treatment was associated with a significant reduction in average displacement (p < 0.05). Significantly greater odds of observing a maximum displacement over 1.22 mm was seen with patients with ECOG > 1, male gender, and increased treatment time (p < 0.05). Age > 65 and anxiolytic use were associated with a significant reduction in maximum displacement (p < 0.05). Performance of clearance checks and use of bite block use did not impact average or maximum patient displacement. Conclusions: This is the first study to evaluate patient and treatment-related factors that influence intrafraction motion during GKRS with mask-based immobilization through HDMM tracking. Increased intracranial displacement during frameless GKRS was associated with higher ECOG, male gender, increased treatment time and malignant tumors, while anxiolytics were shown to mitigate excessive motion. Radiosurgery teams should consider these patient factors when treating patients with mask immobilization. [ABSTRACT FROM AUTHOR]

Background: Cerebral arteriovenous malformations or angiomas are congenital vascular anomalies defined by abnormal arteriovenous shunt. Materials and methods: We conducted a retrospective study between January 1992 and December 2010 at the Timone Hospital radiosurgery unit, 1557 patients were treated by radiosurgery for arteriovenous malformation of which 53 for thalamic localization (3,4%). Results: The mean age was 35.8-/+16.6 years (4-75). 14 patients underwent pre-radiosurgical embolization (26.4%), discovery mode for 47 patients (88.7%) was haemorrhage. The average treatment volume was 1.43 cm3. The average RBAS score was 1.36. The average prescription to the 50% isodose envelope delivered was 22.9 +/-2.9 Gy (12-30), the median margin dose was 24 Gy. Our global obliteration rate after one or two procedures 66.7% for an average follow-up period of 56.7 months. We noted 3.9% of mortality, 5.9% of bleeding after procedure and 3.9% of radioinduced neurological deficit. Conclusion: Radiosurgery became indispensable in the treatment of thalamic AVM even when there is a persistent risk of haemorrhage until total recovery. [ABSTRACT FROM AUTHOR]

Introduction: Stereotactic radiosurgery (SRS) for brain metastases is predominantly delivered via single-fraction Gamma Knife SRS (GKRS) or linear accelerator (LINAC) in up to five fractions. Predictors of SRS modality have been sparsely examined on a nationwide level. Methods: An observational cohort study was performed on patients receiving SRS for brain metastases from non-small cell lung cancer from 2010 to 2016 at Commission on Canceraccredited hospitals throughout the United States (US). A multivariable logistic regression model characterized SRS receipt, adjusting for patient age, dose, geographic location of treatment, facility type, and distance from treatment facility. Results: A total of 2,684 patients received GKRS, while 1,643 patients received LINAC SRS. After adjusting for significant covariates, treatment at non-academic facilities was associated with increased LINAC SRS receipt, most prominently in the Midwestern (OR=6.23;p<0.001), Northeastern (OR=4.42;p<0.001), and Southern US (OR=1.96;p<0.001). Compared to patients receiving 12-17 Gy, patients receiving doses of 18-19 Gy (OR=1.42;p=0.025), 20-21 Gy (OR=1.82;p<0.001), and 22- 24 Gy (OR=3.11;p<0.001) were more likely to receive LINAC SRS; similarly, patients located within 20 miles of a radiation treatment facility were more likely to receive LINAC SRS (OR=1.27;p=0.007). Conclusions: Despite Gamma Knife being more prominently used over LINAC for SRS, patients treated at a non-academic facility outside of the Western US or requiring increased radiation dose were substantially more likely to receive LINAC over Gamma Knife. Additionally, patients residing in close proximity to a treatment center were 27% more likely to receive LINAC, likely indicative of the increased geographic accessibility of LINAC compared with GKRS. [ABSTRACT FROM AUTHOR]

Aim: The aim of this investigation was to develop a standardised method for using the inverse planning module in Leksell GammaPlan. Methods: Leksell GammaPlan version 10 and higher contains an inverse planning module, consisting of functions to automatically fill a target volume with shots and subsequently optimise their resulting dosimetry. A standardised method for using the inverse planning module was developed for metastases, using the following optimisation parameter weightings: {coverage 0.9, selectivity 0.1, gradient index (GI) 0.2, }. 25 plans produced using these parameters were compared to manually produced clinical plans. Additionally, the 25 plans were manually adjusted to match the coverage of the clinical plans, and comparison of the PCI, GI and BOT was made. Results: The average parameters for plans produced using the optimisation module were; coverage 98.7%; Paddick conformity index (PCI) 0.85; GI 2.75, compared to coverage 99.5%; PCI 0.83; GI 2.70 for manual clinical plans with BOT 21% shorter than clinical plans on average. The average parameters for the plans produced by the optimisation module after manual adjustment to match the coverage of the clinical plans were: coverage 99.5, PCI 0.83, GI 2.73 with BOT 16% shorter than clinical plans on average. Conclusions: The standardised method for using the optimisation module has potential for shortening treatment times and planning times. [ABSTRACT FROM AUTHOR]

Purpose: Follow-up imaging after stereotactic radiosurgery (SRS) is crucial to identify salvageable brain metastases (BM) recurrence. As optimal imaging intervals are poorly understood, we sought to build a predictive model for time to intracranial progression. Methods: Consecutive patients treated with SRS for BM at three institutions from January 1, 2002 to June 30, 2017 were retrospectively reviewed. We developed a model using stepwise regression that identified four prognostic factors and built a predictive nomogram. Results: We identified 755 patients with primarily non-small cell lung, breast, and melanoma BMs. Factors such as number of BMs, histology, history of prior whole-brain radiation, and time interval from initial cancer diagnosis to metastases were prognostic for intracranial progression. Per our nomogram, risk of intracranial progression by 3 months post-SRS in the high-risk group was 21% compared to 11% in the low-risk group; at 6 months, it was 43% versus 27%. Conclusion: We present a nomogram estimating time to BM progression following SRS to potentially personalize surveillance imaging. [ABSTRACT FROM AUTHOR]

Background: Stereotactic radiosurgery (SRS) is indicated for a spectrum of brain tumors and is often an outpatient procedure, though severe disease may precipitate inpatient treatment. Readmission following inpatient SRS for brain tumors is not well understood. Objectives: To characterize rate, associative factors, and predictors of SRS readmission. Methods: Retrospective analysis of inpatients treated with SRS for brain neoplasms was conducted (2010-2014 Nationwide Readmissions Database). Diagnoses upon readmission were characterized. Associations with 30-day readmission were identified using multivariate analyses. Results: Of 2,553 patients undergoing SRS, 390 were readmitted (15.3%) within 30 days. Leading readmission diagnoses were infectious or embolic. Neurological readmissions of intracerebral hemorrhage (2.1%) and cerebral edema (1.5%) were rare. Malignant tumors (OR=1.60, p=0.007) and discharge to facility (OR=1.41, p=0.004) were associated with readmission. Conclusion: Inpatients receiving SRS for brain tumors have a 15.3% 30-day readmission rate. Neurologic readmissions were rare, underscoring the neurological safety of SRS, even in sick inpatients. [ABSTRACT FROM AUTHOR]

Introduction: Vestibular schwannomas (VS) are benign tumors with a slow growth rate. There exists controversy regarding whether patients should receive upfront observation, SRS, FSRT, or surgery at the time of diagnosis. For patients declining resection, this systematic review evaluates the risks and benefits between observation and SRS upon diagnosis of VS. Methods: Published studies on VS (including acoustic neuromas) were systematically reviewed for clinical series including patients with newly/recently diagnosed unilateral VS. Studies that included patients with previous treatment for the VS or focused on patients with neurofibromatosis (or other genetic conditions) were excluded. Review articles and systematic reviews were excluded but reviewed for relevant references that would otherwise meet search criteria. Results: Most patients electing observation underwent their first surveillance scan 6 months after initial diagnosis, then annually or every-other-year thereafter. Follow up was similar for patients receiving radiosurgery. The follow up period varied between studies as not all studies published at a specific time point. Observation alone conferred a radiographic tumor control rate of 65% and serviceable hearing in 71.3% at by the end of the follow up period in the reviewed studies, and 34% of patients initially opting for observation went on to ultimately elect for treatment. Initial radiosurgery resulted in a tumor control rate of 97% and serviceable hearing rate of 73.8% at by the end of the follow up period. Radiosurgery resulted in improved tumor control at the end of the follow up period (p < 0.0001), and serviceable hearing did not statistically differ (p = 0.69). There is an early risk of progressive hearing decline on patients who chose initial observation. Conclusion: Based on the available published data, observation after initial diagnosis is appropriate for many patients with VS without symptomatic brainstem compression. However, initial observation does risk early progressive hearing dysfunction and patients with serviceable hearing at diagnosis may benefit from early therapy. Long term follow up is critical, and an algorithm to better riskstratify patients with newly diagnosed VS is underway. [ABSTRACT FROM AUTHOR]

Purpose: To estimate the combined effect of setup uncertainty on optimal dosimetric margin by analyzing the dose distribution and biological effect in LINAC-based stereotactic radiosurgery (SRS) with dynamic conformal arc (DCA) technique. Methods: SRS treatment plans were generated from CT scans of the Rando head phantom using four non-coplanar DCA's with total 480-degrees of arc. A single spherical planning target volume (PTV) of 4 different diameters was placed at the center of the phantom to simulate brain lesions. For each PTV, 5 treatment plans were created using identical dose calculation parameters, each with 5 different dosimetric margins. To simulate the effect of setup uncertainty, the isocenter for each plan was shifted to 13 different positions. A marginal dose of 20Gy in a single fraction with 6MV photon beam was prescribed to 49 different percentage isodose surfaces (%IDS). The plan quality was evaluated using Conformity Index (CI), Gradient Index (GI), EUD-based Tumor Control Probability (TCP), Normal Tissue Complication Probability (NTCP), and uncomplicated biological objective function (TCP x (1-NTCP) =p+). Results: A +1mm dosimetric margin could result in a much higher p+ compared to 0mm and -1mm dosimetric margins and a smaller GI while achieving an equivalent p+ in a certain range of %IDS compared to +2mm and +3mm dosimetric margins. With 2mm setup error and +1mm dosimetric margin, the %IDS range optimized for each PTV is: around 80%IDS (10mm diameter); 63~70%IDS (20mm diameter); 66~79%IDS (30mm diameter). Conclusion: This simulation study identified the preferred prescription %IDS for a given setup error and dosimetric margin to achieve an optimal dose distribution and favorable biological effect. [ABSTRACT FROM AUTHOR]

Introduction: In the present study, we reviewed the efficacy of stereotactic radiosurgery (SRS) alone or in combination with WBRT, for the treatment of patients with BM secondary to SCLC. We further identified patient and treatment specific factors that correlated with improved survival. Methods: Forty-one patients treated with GKRS for BM secondary to SCLC from 2004 to 2017 at the University of Virginia were identified with histopathologically proven SCLC and included in the study. Results: Following the first GKRS treatment, the median survival was 6 months (1-41 months). There was no statistical difference in overall survival and tumor control between the patients who had PCI, WBRT or upfront GKRS. The only factor associated with decreased OS after the diagnosis of BM from SCLC was active extracranial disease (P=0.045, HR=2.354). Conclusion: Stereotactic radiosurgery is a reasonable treatment option for patients with brain metastases of SCLC who had PCI or WBRT failure. [ABSTRACT FROM AUTHOR]

Purpose: We aimed to determine the efficacy of gamma knife stereotactic radiosurgery (SRS) to control brain metastases (BM) from GI primaries and report on the patient outcomes. Materials/methods: We retrospectively evaluated patients who had undergone SRS at our institution for the treatment BM from GI primaries from 2000 to 2016. Actuarial rates for overall survival (OS) and local control (LC) were calculated. Survival rates were computed via the Kaplan-Meier method from the day of SRS. Multivariate analysis (MVA) using proportional hazards regression was done to determine prognostic factors for OS and LC. Results: 53 patients with a total of 148 BM were treated with SRS. The median age at SRS was 60 years and the median treatment dose was 18 Gy. SRS was given as an adjuvant treatment to 30.4% of lesions. Twelve patients underwent second course of SRS for new/recurrent lesions at a median of 8 months from the first SRS (range 2-25.5). Twelve patients (22.6%) received salvage whole brain radiation. The median follow up time from the diagnosis of BM was 6 months. Local control rate at 6 months was 74.33% and 57.21% at 12 months. The OS at 1 year was 34% and 8% at 3 years. On MVA, higher GK dose was associated with better LC, and and >10 BM trended towards higher risk of local recurrence (LR). None of the tested factors proved to be significant for OS on MVA. No radiographic radionecrosis was observed on follow up MRI. Conclusions: SRS is a safe treatment modality for the management of CNS metastases from GI primary. Consideration for dose-escalated approaches may improve LC rates. [ABSTRACT FROM AUTHOR]

Purpose: To compare clinical outcomes following stereotactic radiosurgery (SRS) and fractionated stereotactic radiosurgery (fSRS) for vestibular schwannomas (VS). Materials/methods: We identified 64 VS patients from the RSSearch Patient Registry (12 treated with SRS and 52 patients treated with fSRS). Potential factors predictive of local control (LC) and toxicity were estimated using the Kaplan-Meier method, Cox proportional hazards model, and binary logistic regressions with propensity score weighting. Results: SRS (100%) and fSRS (94.2%) resulted in similar LC (p = 0.33). fSRS was associated with a higher likelihood of experiencing toxicities (42.3% vs. 8.3%; p = 0.054 on time-to-event analysis) that was maintained following a propensity-score weighted binary logistic regression (p = 0.037) and propensity-score weighted Cox regression (p = 0.039; hazard ratio (HR) = 8.85 (95% CI: 1.1 - 70.1)). Conclusion: In a multi-institutional analysis, we note equivalent LC but higher toxicity with fSRS compared to SRS for VS. [ABSTRACT FROM AUTHOR]