Stereotactic Radiosurgery Techniques Research Articles

RADT-45. INTEGRATION OF FUNCTIONAL MAGNETIC RESONANCE IMAGING INTO STEREOTACTIC RADIOSURGERY PLANNING TO REDUCE SYMPTOMATIC RADIATION NECROSIS

Abstract BACKGROUND Radiation necrosis (RN) is a common complication of stereotactic radiosurgery (SRS). Functional magnetic resonance imaging (fMRI) localizes eloquent cortical areas for neurosurgical planning but is seldom applied to SRS. We explored the relationship between symptomatic RN and functional neuroanatomy on fMRI. We evaluated the potential benefit of reducing radiation dose to functional areas. METHODS From 2011 to 2022, patients with an fMRI within 3 months of SRS for resected or unresected brain metastases (BM) were included. The BM nearest to the primary motor, language, or visual cortices was designated as the index BM. The functional area on fMRI nearest to the index BM was designated as the fOAR. Focally symptomatic RN (FSRN) was defined as radiographic RN alongside new or worsening focal neurologic symptoms consistent with the fOAR. Patients treated with 5-fraction SRS and modern planning techniques after 2013 were included in the dosimetric analysis. Associations between fOAR dose and FSRN were evaluated with logistic regression. SRS replanning was performed to determine if fOAR dose could be reduced without sacrificing target coverage. RESULTS Among 94 patients, 82% received SRS postoperatively, and 71% received 5-fraction SRS. fOARs included the primary motor (77%), language (19%), and visual (2%) cortices. Of 20 patients with radiographic RN, 20% were neurologically asymptomatic, 20% had anatomically unrelated neurologic symptoms, and 60% had FSRN. The dosimetric analysis included 39 patients. The fOAR volume receiving a single-fraction equivalent dose ≥14 Gy (V14Gy) was associated with FSRN at 18 months post-SRS (OR=6.8/mL, p=0.05). Replanning reduced fOAR V14Gy in all cases. The mean reduction was 28%. CONCLUSION Neurologic symptoms of SRS-induced RN reflect nearby functional neuroanatomy on fMRI. Dose reduction to functional areas while maintaining target coverage is consistently achievable and may mitigate symptomatic RN. Integrated fMRI-based SRS planning may protect neurologic function when treating tumors near eloquent areas.

Advancements in radiosurgery for the treatment of arteriovenous malformations

Arteriovenous malformations (AVMs) are complex vascular anomalies with high risks of hemorrhage and neurological deficits. The evolution of stereotactic radiosurgery (SRS) represents a significant advancement in their management, offering a less invasive alternative to traditional surgical approaches. This study aims to evaluate recent developments in SRS techniques for treating AVMs by conducting an integrative literature review. Utilizing the PICO strategy, a systematic search was performed across databases like LILACS, MEDLINE, and SCIELO, focusing on clinical trials, observational studies, meta-analyses, and systematic reviews. The analysis revealed that while microsurgical excision remains a definitive approach, SRS—particularly with advanced systems like Gamma Knife, Linac, CyberKnife, and Zap-X—has shown promising results in reducing hemorrhage rates and lesion volumes with lower complications. The findings indicate that SRS, bolstered by improved imaging and radiation precision, provides a viable alternative to invasive methods, though its effectiveness varies among different systems. This review underscores the need for a multidisciplinary approach in AVM management, emphasizing tailored treatment strategies based on lesion characteristics and patient-specific factors.

Evaluating effectiveness of clustering algorithms in multiple target stereotactic radiosurgery

Objective. Single-isocenter-multiple-target technique for stereotactic radiosurgery (SRS) can reduce treatment duration but risks compromised dose coverage due to potential rotational errors. Clustering targets into two groups can reduce isocenter-target distances, mitigating the impact of rotational uncertainty. However, a comprehensive evaluation of clustering algorithms for SRS is absent. This study addresses this gap by introducing the SRS Target Clustering Framework (Framework), a comprehensive tool that utilizes commonly used clustering algorithms to generate efficient cluster configurations. Approach. The Framework incorporates four distinct optimization objectives based on two key metrics: the isocenter-target distance and the ratio of this distance to the target radius. Agglomerative and weighted agglomerative clustering are employed for minimax and weighted minimax objectives, respectively. K-means and weighted k-means are utilized for sum-of-squares and weighted sum-of-squares objectives. We applied the Framework to 126 SRS plans, comparing results to ground truth solutions obtained through a brute force algorithm. Main results. For the minimax objective, the average maximum isocenter-target distance from agglomerative clustering (4.8 cm) was slightly higher than the ground truth (4.6 cm). Similarly, the weighted agglomerative clustering achieved an average maximum ratio of 15.1 compared to the ground truth of 14.6. Notably, both k-means and weighted k-means clustering showed close agreement (within a precision of 0.1) with the ground truth for average root-mean-square target-isocenter distance and ratio (3.6 cm and 11.1, respectively). Significance. These results demonstrate the Framework’s effectiveness in generating clusters for SRS targets. The proposed approach has the potential to become a valuable tool in SRS treatment planning. Furthermore, this study is the first to investigate clustering algorithms for both minimizing maximum and sum-of-squares uncertainty in SRS.

Stereotactic radiosurgery for intracranial dural arteriovenous fistulas: patient outcomes and lessons learned over a 3-decade single-center experience.

The role of stereotactic radiosurgery (SRS) in the management of intracranial dural arteriovenous fistula (dAVF) is unclear given the rarity of this lesion and the variability in treatment paradigms. This study describes a 3-decade experience with the SRS technique and its outcomes for patients with dAVF. The authors conducted a retrospective analysis of patients with dAVF who had undergone single-fraction SRS in the period from 1990 to 2021. The imaging modality initially used for targeting was angiography alone, then angiography plus MRI, and most recently MRI alone. Two hundred twenty-two patients underwent SRS alone (n = 56, 25%) or SRS plus embolization (n = 166, 75%), depending on the severity of symptoms or the presence of cortical venous drainage (CVD). Most patients were women (64%), and the median patient age was 60 years. Common presenting symptoms were pulsatile bruit (55%), visual change or chemosis (21%), headache (10%), and intracerebral hemorrhage (5%). The most frequent dAVF location was the transverse or sigmoid sinus (44%), followed by the cavernous sinus (24%), jugular bulb (9%), and torcula (5%). CVD was noted in 28% of cases, and venous ectasia in 5%. Borden dAVF types among the patients were I (72%), II (20%), and III (8%). Cognard dAVF types among the patients were I (44%), IIa (27%), IIb (5%), IIa+b (15%), III (4%), and IV (5%). The median SRS treatment volume was 7.6 cm3; the median margin and maximum doses were 18 and 36 Gy, respectively. Follow-up after SRS was available for 209 patients (median follow-up 31 months). Obliteration was noted in 75% of the patients (110/147) with follow-up vascular imaging; the median time to obliteration was 37 months. Multivariate analysis revealed that a cavernous sinus dAVF location was predictive of radiological obliteration (HR 1.86, 95% CI 1.08-3.18, p = 0.024). The absence of CVD was predictive of obliteration in subgroup analysis of non-cavernous sinus dAVF (HR 0.53, 95% CI 0.29-0.98, p = 0.04). Symptoms resolved in 86% of patients (160/185) with clinical follow-up. Twelve patients (5.4%) had complications related to angiography for SRS planning (n = 2, 0.9%), embolization (n = 3, 1.4%), post-SRS hemorrhage (n = 1, 0.5%), delayed sinus thrombosis (n = 1, 0.5%), radiation-induced tumors (n = 2, 0.9%), and chronic encapsulated expanding hematoma (n = 3, 1.4%). SRS alone or in conjunction with embolization provided obliteration and symptom relief for the majority of patients with dAVF, with a low rate of procedure-related morbidity. Patients are at risk for late radiation-related complications, which can require treatment many years after SRS.

Evaluation of improvements in plan quality with Photon Optimizer v16.1 for single brain lesion SRS treatment.

The purpose of this study is to compare the performance of the Photon Optimizer (PO) version 16.1 algorithm with its earlier version PO v13.6 and with Progressive Resolution Optimizer (PRO) version 13.6 algorithms. 20 patients with single brain lesions treated with the stereotactic radiosurgery (SRS) technique were retrospectively selected for this study. Initially, for all patients volumetric modulated arc therapy (VMAT) SRS plans were generated with the PRO v 13.6 algorithm. Then, all the plans were re-generated with two versions 13.6 and 16.1 of PO algorithm using the same setup and dose-volume optimization objectives as that of PRO with a similar planning approach. The quality of the generated plans was analysed using ICRU 91 plan evaluation parameters and also using dice similarity co-efficient (DSC), centre of mass distance (CMD) between target and prescription isodose line, Monitor units (MU) and brain-gross tumor volume (GTV) 12 Gy volume. Paired Student t-test was used for statistical analysis with 0.05 as a significant value. PO v16.1 improved all the dosimetric parameters studied compared to PO 13.6, the difference is statistically significant for all the parameters (p < 0.05), except for median dose and brain-GTV 12 Gy volume. PO v16.1 also showed statistically significant improvement for all the dosimetric parameters evaluated, except DSC and conformity index (CI), compared to PRO v13.6. The PO v16.1 generated plans are dosimetrically superior to PO v13.6 and PRO v13.6 in terms of target dose coverage and dose gradient with lesser beam modulation and plan complexity for single brain lesion SRS.

A multi-centre stereotactic radiosurgery planning study of multiple brain metastases using isocentric linear accelerators with 5 and 2.5mm width multi-leaf collimators, CyberKnife and Gamma Knife.

This study compared plans of high definition (HD), 2.5 mm width multi-leaf collimator (MLC), to standard, 5 mm width, isocentric linear accelerator (linacs), CyberKnife (CK), and Gamma Knife (GK) for stereotactic radiosurgery (SRS) techniques on multiple brain metastases. Eleven patients undergoing SRS for multiple brain metastases were chosen. Targets and organs at risk (OARs) were delineated and optimized SRS plans were generated and compared. The linacs delivered similar conformity index (CI) values, but the gradient index (GI) for HD MLCs was significantly lower (P-value <.001). Half the OARs received significantly lower dose using HD MLCs. CK delivered a significantly lower CI than HD MLC linac (P-value <.001), but a significantly higher GI (P-value <.001). CI was significantly improved with the HD MLC linac compared to GK (P-value = 4.591 × 10-3), however, GK delivered a significantly lower GI (P-value <.001). OAR dose sparing was similar for the HD MLC TL, CK, and GK. Comparing linacs for SRS, the preferred choice is HD MLCs. Similar results were achieved with the HD MLC linac, CK, or GK, with each delivering significant improvements in different aspects of plan quality. This article is the first to compare HD and standard width MLC linac plans using a combination of single isocentre volumetric modulated arc therapy and multi-isocentric dynamic conformal arc plans as required, which is a more clinically relevant assessment. Furthermore, it compares these plans with CK and GK, assessing the relative merits of each technique.

Deep-learning-driven dose prediction and verification for stereotactic radiosurgical treatment of isolated brain metastases

PurposeWhile deep learning has shown promise for automated radiotherapy planning, its application to the specific scenario of stereotactic radiosurgery (SRS) for brain metastases using fixed-field intensity modulated radiation therapy (IMRT) on a linear accelerator remains limited. This work aimed to develop and verify a deep learning-guided automated planning protocol tailored for this scenario.MethodsWe collected 70 SRS plans for solitary brain metastases, of which 36 cases were for training and 34 for testing. Test cases were derived from two distinct clinical institutions. The envisioned automated planning process comprised (1): clinical dose prediction facilitated by deep-learning algorithms (2); transformation of the forecasted dose into executable plans via voxel-centric dose emulation (3); validation of the envisaged plan employing a precise dosimeter in conjunction with a linear accelerator. Dose prediction paradigms were established by engineering and refining two three-dimensional UNet architectures (UNet and AttUNet). Input parameters encompassed computed tomography scans from clinical plans and demarcations of the focal point alongside organs at potential risk (OARs); the ensuing output manifested as a 3D dose matrix tailored for each case under scrutiny.ResultsDose estimations rendered by both models mirrored the manual plans and adhered to clinical stipulations. As projected by the dual models, the apex and average doses for OARs did not deviate appreciably from those delineated in the manual plan (P-value≥0.05). AttUNet showed promising results compared to the foundational UNet. Predicted doses showcased a pronounced dose gradient, with peak concentrations localized within the target vicinity. The executable plans conformed to clinical dosimetric benchmarks and aligned with their associated verification assessments (100% gamma approval rate at 3 mm/3%).ConclusionThis study demonstrates an automated planning technique for fixed-field IMRT-based SRS for brain metastases. The envisaged plans met clinical requirements, were reproducible across centers, and achievable in deliveries. This represents progress toward automated paradigms for this specific scenario.

Frameless Linear Accelerator (LINAC) Based Radiosurgery (SRS) vs. Framed Gamma Knife SRS for Idiopathic Trigeminal Neuralgia (TN)

Stereotactic radiosurgery (SRS) is an effective treatment for idiopathic trigeminal neuralgia (TN). Conventional treatment is done through frame-based solution due to small target and high radiation dose. More recently, LINAC based frameless SRS technique has been established as a patient friendly alternative. Herein we compared our single institution experience of LINAC based frameless SRS vs frame-based gamma knife SRS for TN. The hypothesis is LINAC based frameless SRS can provide equivalent dosimetric and clinical outcome as compared frame-based gamma knife treatment. Patients with idiopathic TN who received SRS treatment (LINAC based frameless treatment or Gamma knife framed treatment) at our institution from 2015-2022 were included. A minimum follow up of 1 year was required. Patient data was extracted from electronic medical records and radiation treatment planning system. Pain intensity was evaluated utilizing a modified 0-4 Barrow Neurological Institute (BNI) pain intensity score, and then dichotomized where BNI score 0-2 represented response to treatment and BNI score 3-4 represented no response. Statistical analysis was conducted with a linear regression model accounting for race, gender, prior pain, pain distribution including laterality and branch involvement, medication regimen at time of treatment, previous radiation treatment, and prior procedures. Response was then compared between both modalities overall and within each sub-group with chi-square testing and linear regression. A total of 81 patients were identified, 14 patients were excluded due to lack of adequate follow-up, leaving 67 for analysis. 12 (17.9%) were male and, 55 (82.1%) were female. All patients were managed with medication prior to SRS treatment. 5 (7.5%) had rhizotomy and 13 (19.4) had microvascular decompression, and 8 (11.9%) had previous gamma-knife radiosurgery prior to SRS treatment at our institution. Of the 67 patients, 23 (34.3%) received frame-based gamma knife SRS, 44(65.7%) received frameless LINAC treatment. 58 (86.6%) radiation naïve patients received 90 Gy in 1 fraction, while out of the 9 who had previously had intracranial radiation treatment 7 (10.4%) received 70 Gy and 2 (3%) received 80 Gy all prescribed to 100% isodose line. All patients were treated with 4 mm cone. There was no significant difference in brainstem dose between these two techniques. Between LINAC-based or Gamma Knife modalities rate of pain control (77.3 % vs 82.6 %, respectively, p = 0.61) as well as toxicity in facial numbness (31.8% vs 21.7%, respectively, p = 0.38) showed no statistical difference. There was no statistically significant signal (p > 0.05) detected within the subgroups analyzed. The linear regression model also showed no significant difference. LINAC based frameless SRS provides comparable dosimetry and pain control for TN as compared to frame-based gamma knife treatment. It is a patient friendly solution for patients with TN.

Endocrine-inactive pituitary tumors: pathology and current approaches to diagnosis and treatment

pathological hormone secretion, the clinical presentation is determined by the localization of the tumor. Common symptoms include headache and visual field defects. This review addresses the pathology aspects of diagnosis, conservative treatment, and methods of radiation therapy. Drug therapy of endocrine-inactive adenomas is based on the presence of receptors for somatostatin and dopamine in pituitary adenoma cells. Data on stereotactic radiosurgery techniques such as gamma and cyberknife and disease prognosis are presented.

SRS for Cavernous Malformations: Myths and Realities.

The optimal management of cavernous malformations (CMs) remains controversial. Over the past decade, stereotactic radiosurgery (SRS) has gained wider acceptance in the management of CMs, especially in those with deep location, eloquence, and where surgery is of high risk. Unlike arteriovenous malformations (AVMs), there is no imaging surrogate endpoint to confirm CM obliteration. Clinical response to SRS can only be gauged by a reduction in long-term CM hemorrhage rates. There is concern that the long-term benefits of SRS and the reduced rehemorrhage rate after a latency period of 2 years may only be a reflection of natural history. Of further concern is the development of adverse radiation effects (AREs), which were significant in the early experimental studies. The lessons learnt from that era have led to the progressive development of well-defined, lower marginal dose treatment protocols that have reported less toxicity (5%-7%) and consequently reduced morbidity. Currently, there is at least Class II, Level B evidence for use of SRS in solitary CMs with previous symptomatic hemorrhage in eloquent areas with high surgical risk. Recent prospective cohort studies observing untreated brainstem and thalamic CMs report significantly higher hemorrhage rates and neurological sequelae than the rates reported from contemporary pooled large natural history meta-analyses. Furthermore, this strengthens our recommendation for early proactive SRS in symptomatic deep-seated CMs due to the higher morbidity associated with observation and microsurgery. The key to successful outcomes for any surgical intervention is patient selection. We hope that our precis on contemporary SRS techniques in the management of CMs will assist this process.

Modified Dynamic Conformal Arcs With Forward Planning for Radiosurgery of Small Brain Metastasis: Each Double Arc and Different To-and-Fro Leaf Margins to Optimize Dose Gradient Inside and Outside the Gross Tumor Boundary.

Dynamic conformal arcs (DCA) are a widely used technique for stereotactic radiosurgery (SRS) of brain metastases (BM) using a micro-multileaf collimator (mMLC), while the planning design and method considerably vary among institutions. In the usual forward planning of DCA, the steepness of the dose gradient outside and inside the gross tumor volume (GTV) boundary is simply defined by the leaf margin (LM) setting to the target volume edge. The dose fall-off outside the small GTV tends to be excessively precipitous, especially with an MLC of 2.5-mm leaf width, which is predisposed to the insufficient coverage of microscopic brain invasion and other inherent inaccuracies. Meanwhile, insufficient dose increase inside the GTV boundary, i.e., less inhomogeneous GTV dose, likely leads to inferior and less sustainable tumor response. The more inhomogeneous GTV dose is prone to the steeper dose gradient outside the GTV and vice versa. Herein, we describe an alternative simply modified DCA (mDCA) planning that was uniquely devised to optimize the dose gradient outside and inside the GTV boundary for further enhancing and consolidating local control of small BM. For a succinct exemplification, a 10-mm spherical target was assumed as a GTV for DCA planning using a 2.5-mm mMLC. The benchmark plan was generated by adding a 0-mm LM to the GTV edge byassigning a single fraction of 30 Gy to the isocenter, in which the GTV coverage by 24 Gy with 80% isodose surface (IDS) was 96%, i.e., D96%, while the coverage of GTV + isotropic 2 mm volume by 18 Gy with 60% IDS was 70%, with the D98% being 12 Gy with 40% IDS, viz., too steep dose fall-off outside the GTV boundary. Alternatively, the increase of LM with or without decreasing the isocenter dose enablesthe increase of the GTV + 2 mm coverage by 18 Gy while resulting in an inadequate GTV dose with either a less inhomogeneous dose or an excessive marginal dose. Meanwhile, in the newly devised mDCA planning, everysingle arc was converted to a double to-and-fro arcwith different LM settings under the same spatial arrangement, which enabled GTV + 2 mm volume coverage with 18 Gy while preserving the GTV marginal dose and inhomogeneity similar to those for the benchmark plan. Additionally, the different collimator angle (CA) setting for the to-and-fro arcs led to further trimming of the dose conformity. The limitations of general forward planning with only adjusting the LM for everysingle arc were demonstrated, which can be a contributing factor for local tumor progressionof small BM. Alternatively, the mDCA with each double to-and-fro arc and different LM and CA settings enables optimization of the dose gradient both outside and inside the GTV boundary according to the planners' intent, e.g., moderate dose spillage margin outside the GTV and steep dose increase inside the GTV boundary.

A simplified and effective off-axis Winston-Lutz for single-isocenter multi-target SRS.

To safely perform single-iso multi-target (SIMT) stereotactic radiosurgery (SRS), clinics must demonstrate SRS delivery accuracy for off-axis targets. The traditional Winston-Lutz (W-L) was widely adopted because it provides a simple and accurate solution for testing radiation-isocenter coincidence that uses a static target, enables testing arbitrary treatment angles, and does not require expensive commercial phantoms. The current noncommercial tests are cumbersome and insufficiently accurate. For an off-axis Winston-Lutz (OAWL) test, one must design MLC fields centered on off-axis targets. Unfortunately, because MLC leaf-interfaces are often misaligned with the target center, accomplishing this presents a nontrivial geometry problem that has not been previously solved in the literature. We present a solution for evaluating SIMT SRS accuracy that provides a straightforward method for creating OAWL test fields and offers all the benefits of the standard W-L test. We have developed a method to use any gantry, table, and initial collimator angles to create OAWL fields. This method calculates a series of nested coordinate transformations that produce a small collimator angle adjustment to align the MLC and create a symmetric field around an off-axis target. For an 8cm off-axis target, the described method yields OAWL results within 0.07mm of standard isocentric W-L results. Our six most recent isocentric W-L tests show max and mean errors of 0.59 and 0.37mm, respectively. For six runs of our proposed OAWL test, the average max and mean errors are 0.66 and 0.40mm, respectively. This method accurately evaluates SRS delivery accuracy for off-axis distances that span the majority of a typical human brain for a centered SIMT arc. We have made this method publicly available, so that physicists can employ it within their clinics, foregoing the need for expensive phantoms and improving access to the state-of-the-art SIMT SRS technique.

Analysis of Survival Outcomes of Patients Treated with Stereotactic Radiosurgery for High Volume Brain Metastases

<h3>Purpose/Objective(s)</h3> To analyze outcomes and assess for factors associated with improved survival in patients with greater than or equal to 20 cumulative brain metastases treated with stereotactic radiosurgery (SRS). <h3>Materials/Methods</h3> This was a single institution, retrospective analysis that included patients with 20 or more cumulative brain metastases treated with SRS. Between December 2015 and February 2022, 96 patients were identified that met the inclusion criteria, and their clinical, tumor, and treatment data were used for analysis. Overall survival outcomes, defined as the time interval from initial SRS treatment until death from any cause, were calculated using the Kaplan-Meier method for various patient, tumor, and treatment factors. The log-rank test was used to compare subgroups and investigate patient characteristics for significance. <h3>Results</h3> The median follow-up time, defined as the interval between date of initial SRS and last recorded physician follow-up, was 8.7 months. Median ages at time of initial cancer diagnosis, initial brain metastases diagnosis, and initial SRS treatment were 60, 57 and 60 years, respectively. The most common primary tumor histologies were lung (48%) and breast (23%), followed by melanoma (10%), and renal cell carcinoma (8%), with the remaining 10% of patients being grouped together due to rare histology. In regard to treatment characteristics, the median cumulative number of brain metastases was 31.5 (range 20-158) with the median of 22 brain metastases treated in a single SRS treatment course. The majority of patients were treated with a distributed SRS technique (86%). The median number of cumulative SRS sessions was 2 (range 1-7). Median overall survival for the entire cohort was 12.6 months. Categorized by primary histology, the median OS for lung, breast, melanoma, RCC, and other was 14.8, 15.5, 8.9, 22.8, and 6.5 months, respectively (NS, p=0.182). Further analysis of factors associated with overall survival found the presence of a targetable mutation (18.4 vs 10.5 months (HR 0.48, 95% CI 0.29-0.78, p=0.004)) and not having received whole brain radiotherapy (15.5 vs 9.3 months (HR 1.92, 95% CI 1.11-3.33, p=0.008)) as significant predictors of overall survival. ECOG performance status at time of initial SRS (0-1 vs 2) was trending toward significance (13.6 vs 9.7 months (HR 0.93, 95% CI 0.54-1.62, p=0.068) but was not statistically relevant. <h3>Conclusion</h3> Treatment of high-volume brain metastases with SRS appears to be safe and is feasible in selected patient populations. Survival rates appear comparable to prospective studies utilizing upfront conventional whole brain and hippocampal sparing radiation. Further studies are needed to validate this approach and identify patients best suited for this treatment paradigm.

Stereotactic radiosurgery and radiotherapy for resected brain metastases: current pattern of care in the Radiosurgery and Stereotactic Radiotherapy Working Group of the German Association for Radiation Oncology (DEGRO).

Preoperative stereotactic radiosurgery (SRS) of brain metastases may achieve similar local control and better leptomeningeal control rates than postoperative fractionated stereotactic radiotherapy (FSRT) in patients treated with elective metastasectomy. To plan amulticentre trial of preoperative SRS compared with postoperative FSRT, asurvey of experts was conducted to determine current practice. Asurvey with 15questions was distributed to the DEGRO Radiosurgery and Stereotactic Radiotherapy Working Group. Participants were asked under what circumstances they offered SRS, FSRT, partial and/or whole brain radiotherapy before or after resection of abrain metastasis, as well as the feasibility of preoperative stereotactic radiosurgery and neurosurgical resection within 6days. Of 25participants from 24centres, 22completed 100% of the questions. 24respondents were radiation oncologists and1 was aneurosurgeon. All 24centres have one or more dedicated radiosurgery platform and all offer postoperative FSRT. Preoperative SRS is offered by 4/24 (16.7%) centres, and 9/24 (37.5%) sometimes recommend single-fraction postoperative SRS. Partial brain irradiation is offered by 8/24 (33.3%) centres and 12/24 (50%) occasionally recommend whole-brain irradiation. Two centres are participating in clinical trials of preoperative SRS. SRS techniques and fractionation varied between centres. All responding centres currently offer postoperative FSRT after brain metastasectomy. Approximately one third offer single-fraction postoperative SRS and four already perform preoperative SRS. With regard to potential co-investigators, 18 were identified for the PREOP‑2 multicentre trial, which will randomise between preoperative SRS and postoperative FSRT.

The Optimal Choice of Technique for Stereotactic Radiosurgery—A LINAC-Based Dosimetric Study between DCA, DCA-SSO, DCA-SSO-VDR, and VMAT

Abstract Introduction Advanced radiation therapy delivery techniques require greater understanding of various planning sequences and methods. The aim of this study is to determine a class solution that finds the best possible technique to deliver for stereotactic radiosurgery between dynamic conformal arc (DCA) techniques using various options such as DCA, DCA + SSO (segment shape optimization), and DCA + SSO + VDR (variable dose rate) using noncoplanar beam arrangement and volumetric modulated arc therapy (VMAT) using coplanar beams. Materials and Methods In this dosimetric study, 11 brain cases were retrospectively planned for various techniques and analyzed for the Paddick conformity index (CI), Radiation Therapy Oncology Group homogeneity index (HI), Paddick gradient index (GI), treatment time in terms of monitor units (MU) and normal brain dose (V12Gy). The paired t-test was performed to know the statistical significance between the techniques. Results In terms of CI, GI, and control of the normal brain dose, the VMAT plan was superior to other techniques. But, HI was found to be better with DCA. Above all, VMAT delivered higher MU than any other technique. The p-values between DCA + SSO and DCA, DCA + SSO + VDR and DCA + SSO, and VMAT and DCA + SSO + VDR are as follows: CI: 0.0004, 0.015, and 0.03; GI: 0.03, 0.33, and 0.29; HI: 0.008, 0.04, and 0.06; V12 Gy of normal brain: 0.1, 0.01, 0.38. VMAT requires approximately 41 ± 17% more MU than DCA + SSO + VDR. Conclusion VMAT using coplanar beams is preferable among all the techniques, considering the dosimetric parameters studied. If VMAT is not available in the facility, DCA + SSO + VDR technique using non coplanar beams can be used to deliver SRS treatment.

Verification of stereotactic radiosurgery plans for multiple brain metastases using a virtual phantom-based procedure.

BackgroundThe purpose of this study was to describe the use of the VIPER software for patient-specific quality assurance (PSQA) of single-isocenter multitarget (SIMT) stereotactic radiosurgery (SRS) plans.Materials and methodsTwenty clinical of intensity-modulated (IMRT) SIMT SRS plans were reviewed. A total of 88 brain metastases were included. Number of lesions per plan and their individual volumes ranged from 2 to 35 and from 0.03 to 32.8 cm3, respectively. Plans were designed with the Eclipse system, and delivered using a Varian CLINAC linac. SRS technique consisted of non-coplanar static-field sliding-window IMRT. Each plan was mapped onto a virtual cylindrical water phantom (VCP) in the Eclipse to calculate a 3D dose distribution (verification plan). The VIPER software reconstructed the 3D dose distribution inside the VCP from the acquired in-air electronic portal image device (EPID) images of the treatment fields. A 3D gamma analysis was used to compare the reconstructed doses to the Eclipse planned doses on the VCP. Gamma passing rates (GPRs) were calculated using 3% global/2 mm criteria and dose thresholds ranged from 10% to 90% of the maximum dose.ResultsThe averages (± 1 SD) of the 3D GPRs over the 20 SRS plans were: 99.9 ± 0.2%, 99.7 ± 0.3%, 99.6 ± 0.5%, 99.3 ± 0.9%,99.1 ± 1.6%, 99.0 ± 1.6%, and 98.5 ± 3.3%, for dose thresholds of 10%, 20%, 30%, 50%, 70%, 80% and 90% respectively.ConclusionsThis work shows the feasibility of the VIPER software for PSQA of SIMT SRS plans, being a reliable alternative to commercially available 2D detector arrays.

Proton Radiosurgery: A Clinical Transition From Passive Scattering to Pencil Beam Scanning

Our institution developed proton stereotactic radiosurgery (PSRS) techniques and treated patients since 1961. A recent upgrade from passive scattering (PS) delivery to pencil beam scanning (PBS) required validation of this modality for small fields. We describe the adaptation of an existing clinical PSRS service to PBS. We outline potential advantages and disadvantages the modality has to offer.Patient alignment is determined from 2D/3D x-ray corrections of surgically implanted fiducials. End-to-end tests using a skull phantom were performed to validate a change of treatment planning system (TPS). PSRS PS fields from prior years established applicable parameters for dose, range, modulation, field size and aspect ratio for PBS validation. 18 fields were created to verify agreement with the TPS. A diamond detector was used to measure SOBP doses and film to measure profiles. A QA phantom enabled simultaneous measurement with film and diamond detector. X-rays were used to verify detector alignment prior to measurements. A hybrid 2D/3D γ-analysis was used to assess lateral profiles. Plans were generated for previously treated patients and used to perform end-to-end tests. These included 6 AVM, 3 pituitaries and 1 cavernous sinus lesion. Clinical directives were obtained from the original plans.End-to-end phantom tests conformed sub-mm alignment. Distal and proximal depth agreement were 0.10 ± 0.66% and 0.74 ± 0.48 mm. Isocenter and shallow depth dose agreement was -1.7 ± 2.9% and 2.5 ± 5.1%, respectively. Global 2%/1mm/10% γ-analysis resulted in pass rates of 97.2 ± 4.8%. 24 clinical fields were delivered. Dose agreement was -2.8 ± 2.7%. Global 3%/1mm/10% γ- analysis PASS rates were 99.5 ± 1.4%.We have revalidated SRS appropriate fiducial-based alignment and defined a small-field QA process using a diamond detector & film to demonstrate PSRS performed with PBS delivery is accurate. Proton delivery systems and TPS modeling can differ significantly. Therefore, validation and plan quality results should not be generalized to all systems. Proton range uncertainties play an important role in determining the appropriateness of PSRS. PBS does not offer distal benefits for small targets compared to passive scattering using range compensators. Larger SRS targets with irregular shapes may benefit from intensity variations and variable modulation offered by PBS. VMAT generally provides slightly superior target coverage for small pituitary lesion, but target coverage for larger pituitary lesions not abutting the optic structures and prescribed to lower doses are more comparable for VMAT and PBS while lowering integral dose. Our validation effort enabled the transition of an active PSRS program from PS to PBS.M. Bussiere: None. J. Daartz: None. J. Verburg: Employee; Massachusetts General Hospital. Research Grant; National Cancer Institute. N. Depauw: None. H.M. Kooy: None. J.S. Loeffler: Employee; Massachusetts General Hospital. Advisory Board; Mevion. P.H. Chapman: None. H.A. Shih: Employee; Dartmouth Hitchcock. Research Grant; AbbVie, NIH. Honoraria; UpToDate. Consultant; Cleveland Clinic. Speaker's Bureau; prIME Oncology. advisory; The Radiosurgery Society. director of clinical operations; Massachusetts General Hospital. clinical operational leader; Massachusetts General Hospital.

Optimal Scheme in Hypofractionated Stereotactic Radiation Therapy for Brain Metastases

Stereotactic radiosurgery (SRS) is common technique used in the treatment of brain metastases. In lieu of single-fraction SRS, hypofractionated stereotactic radiation therapy (HF-SRT) is employed for large metastases and/or for those in sensitive areas of the brain in order minimize toxicity while maintaining effectual local control (LC) rates. There is currently no consensus on an optimal dose-fractionation, with most of the surrounding evidence being in the form of retrospective institutional studies resulting in a variety of utilized fractionation schemes. Some of these studies have suggested that BED10 may predict for improved LC. Our hypothesis is that HF-SRT delivered to BED10 ≥50 Gy would confer improved LC without a significant detriment in radionecrosis (RN) rates.A search of medical literature in PubMed/MEDLINE, Embase, and Cochrane databases was conducted using Preferred Reporting Items for Systematic Reviews and Meta-Analyses of Observational Studies in Epidemiology (PRISMA) guidelines. Search terms included 'brain metastases and 'radiosurgery' yielding studies which were individually reviewed for inclusion. To meet inclusion, studies must have 1) utilized hypofractionated stereotactic radiosurgery techniques defined as ≥2.5 Gy per fraction in the treatment of brain metastases, 2) described LC and RN rate data, and 3) administered radiosurgery as definitive or post-operative treatment. Linear regression of the logarithmically transformed 1-year LC rate weighted by the number of lesions in each study was performed. In addition, a non-parametric, exact Mann-Whitney U-test was used to test a potential difference in 1-year LC or RN rate according to whether studies achieved a median BED10 ≥50 Gy.A total of 27 studies spanning 2000 to 2019 comprising of 2399 lesions met our inclusion criteria and were analyzed. Median BED10 across all studies was 51.3 Gy (range 37.5 to 69.3), with 836 lesions receiving BED10 < 50 Gy and 1563 lesions BED10 ≥50 Gy. Median total dose and number of treatments were 30 Gy (range 23.1 to 40) and 5 fractions (range 3 to 10), respectively. There was no statistically significant difference in LC with BED10 ≥50 Gy versus BED10 < 50 Gy (2-tailed, P = 0.104), nor was there a difference in reported necrosis rate (P = 0.85). On multivariate analysis of 1-year LC, the only significant factor was volume of tumor treated, where increased tumor volume was associated with increased LC (P = 0.0011).This analysis showed there was no statistically significant difference between dose-fractionation regimens delivering BED10 ≥50 Gy versus BED10 < 50 Gy with regards to 1-year LC and the incidence of RN. Studies appeared heterogeneous and this may explain the unexpected association between increasing tumor volume and LC. Future randomized controlled trials should be conducted to identify the optimal dose-fractionation for patients with large brain metastases.O.M. Siddiqui: None. C. Haskins: None. S.M. Bentzen: Travel Expenses; University of Copenhagen. M.V. Mishra: Employee; Orthofix. Research Grant; ASTRO, Keep Punching. Advisory Board; Patient Centers Outcomes Research Institute (PCORI. Travel Expenses; Patient Centers Outcomes Research Institute (PCORI.

Long-Term Hearing Outcomes From Gamma Knife Treatment for Vestibulocochlear Nerve Schwannomas in a Large, Tertiary Care, Academic Hospital.

Describe long-term hearing outcomes with audiologic data with modern stereotactic radiosurgery techniques for vestibular schwannoma tumors. Since the mid-20th century, stereotactic radiosurgery has been an option for central nervous system tumors. Due to the non-invasive manner of treatment, this was extended to treatment for benign vestibular schwannomas without intracranial surgery. Modern advances have localized radiation and reduced dosage, but data are still lacking in the long-term hearing outcomes of this method of treatment. As one of the national leaders in this procedure, we present our full database of these outcomes over the full time period of our institutions utility of this modality. A retrospective review was performed of all patients undergoing stereotactic radiotherapy for vestibular schwannomas within the study period of 1998 to 2019 and their audiograms analyzed along with patient data. Laterality Gardner-Robertson hearing score changes were the primary outcome analyzed for each patient; and controls were placed to accommodate for patient demographic data. Long-term, multi-year audiometric evaluation showed statistically significant loss of serviceable hearing and reduction in hearing ability with the use of stereotactic radiosurgery for treatment of vestibular schwannomas. Little long-term data exists on the audiometric outcomes related to stereotactic radiosurgery treatment for vestibular schwannomas. Our institution has performed more than 300 stereotactic radiosurgery treatments showing a continued reduction over time in serviceable hearing. Practitioners should advise patients undergoing treatment for vestibular schwannomas with this treatment of long-term results.

Does post-operative radiotherapy improve the treatment outcomes of intracranial hemangiopericytoma? A retrospective study

BackgroundIntracranial hemangiopericytoma is a rare disease and surgery is the mainstay treatment. Although postoperative adjuvant radiotherapy is often used, there are no reports comparing different radiotherapy techniques. The purpose of this study is to analyze the impact of post-operative radiotherapy and different radiotherapy technique on the results in patients with intracranial hemangiopericytoma (HPC).MethodsWe retrospectively reviewed 66 intracranial HPC patients treated between 1999 and 2019 including 29 with surgery followed by radiotherapy (11 with intensity-modulated radiotherapy (IMRT) and 18 with stereotactic radiosurgery (SRS)) and 37 with surgery alone. Chi-square test was used to compare the clinical characteristic between the groups. The Kaplan-Meier method was used to analyze overall survival (OS) and recurrence-free survival (RFS). Multivariate Cox proportional hazards models were used to examine prognostic factors of survival. We also underwent a matched-pair analysis by using the propensity score method.ResultsThe crude local control rates were 58.6% in the surgery plus post-operative radiotherapy group (PORT) and 67.6% in the surgery alone group (p = 0.453). In the subgroup analysis of the PORT patients, local controls were 72.7% in the IMRT group and 50% in the SRS group (p = 0.228). The median OS in the PORT and surgery groups were 122 months and 98 months, respectively (p = 0.169). The median RFS was 96 months in the PORT group and 72 months in the surgery alone group (p = 0.714). Regarding radiotherapy technique, the median OS and RFS of the SRS group were not significantly different from those in the IMRT group (p = 0.256, 0.960). The median RFS were 112 and 72 months for pathology grade II and III patients, respectively (p = 0.001). Propensity score matching did not change the observed results.ConclusionIn this retrospective analysis, PORT did not improve the local control rates nor the survivals. The local control rates after IMRT and SRS were similar even though the IMRT technique had a much higher biological dose compared with the SRS technique.