Frame-based Stereotactic Radiosurgery Research Articles

Response of treatment-naive brain metastases to stereotactic radiosurgery

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

Does the Shift Away From Frame-based Stereotactic Radiosurgery Endanger Radiation Oncology's Seat at the Table in Treating Functional Disorders?

Does the Shift Away From Frame-based Stereotactic Radiosurgery Endanger Radiation Oncology's Seat at the Table in Treating Functional Disorders?

LMAP-14 EFFECT OF TRANSLATIONAL VARIATION ON DOSE CHANGE ADOPTED FOR CONE-BEAM CT GUIDED FRAME BASED STEREOTACTIC RADIOSURGERY OF BRAIN TUMORS

Abstract INTRODUCTION Gamma knife (GK) is a highly precise form of stereotactic radiosurgery (SRS) that delivers high doses of radiation to small, well-defined targets in a variety of tumor and vascular abnormalities. In some frame-based cases, a small translation can occur between the planning MRI and the cone-beam CT acquired at the time of treatment. Measuring the effect of patient translation on the dose distribution may be useful for informing clinical decisions. Materials/ METHODS This retrospective study of 113 planning target volumes (PTV) from 33 patients investigates the effect of translational variation on dose metrics recalculated based on cone-beam CT guided for frame based GK radiosurgery. The approved dose adjustments after the original treatment plan in terms of change in mean dose and dose coverage were compared with corresponding translation variation and the volume of PTV. The magnitude of translational variation was compared with the change in dose distribution. RESULTS We observed about 53% of cases have at least 0.1 Gy to max 1.2 Gy change in mean dose approved for the translation variation of patients while about 20% of cases have dose coverage fraction change in the range of 2-10%. Furthermore, the change in mean dose and coverage fraction is not linear with the translation variation, but a significant number of dose changes is observed when the variation magnitude is >0.5 mm. PTV volume varied between 0.04 to 22 cm3 and the dose change has been most often adopted when the volume is <2.5 cm3 and the change increases for the decreasing PTV volume. CONCLUSION This work provides new insights identifying the suitable tolerance level for translational variations of patients and the resulting impact on the prescribed dose for frame-based SRS.

Frameless versus frame-based stereotactic radiosurgery for intracranial arteriovenous malformations: A propensity-matched analysis.

The frameless linear accelerator (LINAC) based stereotactic radiosurgery (SRS) has been evolving with a reduction in patient discomfort. However, there was limited evidence comparing frame-based and frameless SRS for intracranial arteriovenous malformations (AVM). We aimed to compare the treatment outcomes between frame-based and frameless LINAC SRS. This retrospective cohort compared the outcomes of frame-based LINAC SRS (1998-2009) with frameless LINAC SRS (2010-2020). The primary outcome was the obliteration rate. The other outcomes included the neurological, radiological, and functional outcomes after SRS. A matched cohort was identified by propensity scores for further comparisons. A total of 65 patients were included with a mean follow-up time of 13.2years (158.5months). There were 40 patients in the frame-based group and 25 patients in the frameless group. The overall obliteration rate was comparable (Frame-based 82.5% vs Frameless 80.0%, p=0.310) and not significantly different over time (log-rank p=0.536). The crude post-SRS hemorrhage rate was 1.5% and the incidence was 0.3 per 100 person-years. There were 67.7% of patients with AVM obliteration without new persistent neurological deficits at the last visit and 56.9% of patients with AVM obliteration without any deficits (transient or persistent) during the entire follow-up period. Four patients (8.0%) developed late onset persistent adverse radiation effects (more than 96months after SRS) among 50 patients with more than 8-year surveillance. In the propensity-matched cohort of 42 patients, there was no significant difference in AVM obliteration (Frame-based vs Frameless, log-rank p=0.984). Frameless and frame-based LINAC SRS have comparable efficacy in intracranial AVM obliteration. A longer follow-up duration may further characterize the rate of late adverse radiation effects in frameless SRS.

The Effectiveness and Toxicity of Frameless CyberKnife Based Radiosurgery for Parkinson's Disease-Phase II Study.

Frame-based stereotactic radiosurgery (SRS) has an established role in the treatment of tremor in patients with Parkinson's disease (PD). The low numbers of studies of frameless approaches led to our prospective phase 2 open-label single-arm clinical trial (NCT02406105), which aimed to evaluate the safety and efficacy of CyberKnife frameless SRS. Twenty-three PD patients were irradiated on the area of the thalamic ventral nuclei complex with gradually increasing doses of 70 to 105 Gy delivered in a single fraction. After SRS, patients were monitored for tremor severity and the toxicity of the treatment. Both subjective improvement and dose-dependent efficacy were analysed using standard statistical tests. The median follow-up was 23 months, and one patient died after COVID-19 infection. Another two patients were lost from follow-up. Hyper-response resulting in vascular toxicity and neurologic complications was observed in two patients irradiated with doses of 95 and 100 Gy, respectively. A reduction in tremor severity was observed in fifteen patients, and six experienced stagnation. A constant response during the whole follow-up was observed in 67% patients. A longer median response time was achieved in patients irradiated with doses equal to or less than 85 Gy. Only two patients declared no improvement after SRS. The efficacy of frameless SRS is high and could improve tremor control in a majority of patients. The complication rate is low, especially when doses below 90 Gy are applied. Frameless SRS could be offered as an alternative for patients ineligible for deep brain stimulation; however, studies regarding optimal dose are required.

Frameless Co-Registration of Biplane 2D Digital Subtraction Angiography Whole Frames and 3D Rotational Angiography-Based Cone-Beam Computed Tomography Angiogram on Dedicated Software for Stereotactic Radiosurgery of Cranial Vascular Malformations.

Purpose: Given its high spatial resolution and vasculature selectivity, the cone-beam computed tomography (CT) angiography (CBCTA) image acquired by selective 3D rotational angiography (3DRA) is the most suitable 3D image for the target definition of stereotactic radiosurgery (SRS) for intracranial arteriovenous malformations (AVMs) and dural arteriovenous fistulas (DAVFs). Furthermore, the relatively low temporal resolution of 3DRA-based CBCTA can be complemented by the stereotactic co-registration of orthogonally paired 2D dynamic digital subtraction angiography (2D-DSA). The integration of 2D-DSA, which is usually limited to one or a few frames for each projection, into CBCTA and/or planning CT can be achieved only by catheter-directed angiography on the day of SRS via a dedicated image localizer under rigid frame fixation to the skull, which imposes substantial burdens on patients. This study aimed to demonstrate a novel, convenient, and significantly less invasive method for the frameless co-registration of biplane 2D-DSA whole frames and CBCTA on commercially available dedicated software, namely, Brainlab® Elements (Brainlab AG, Munich, Germany), and present its prerequisite for successful image fusion.Technical Report: Elements have afforded the following functionality: A 3D vasculature image is automatically extracted as a floating image from any 3D image series containing vascular details and then subsequently co-registered manually and automatically to a selected frame pair of 2D-DSA with a six-degree-of-freedom rigid registration. As a preclinical feasibility study, two anonymous image datasets from patients harboring cerebral AVM and transverse-sigmoid (TS) DAVF were used to verify the accuracy and practicality of Elements for the frameless co-registration of 2D/3D vascular images, particularly on the assumption of clinical workflow for the target delineation of SRS planning. The use of ordinary unsubtracted CBCTA resulted in the insufficient extraction of abutting vessels or vessels that are in close proximity to bony structures, particularly in the case of TS-DAVF, where the fistulous pouch and the affected venous sinuses were adjacent to the cranial bone. By contrast, the amount and selectivity of vasculatures and the accuracy of subsequent image fusion were significantly improved from the subtracted CBCTA. The integration of CBCTA into dynamic 2D-DSA allowed the simultaneous review of both image information by sharing any concerning point and 2D or 3D structures under a common 3D coordinate.Conclusions: Elements enable the clinically useful frameless co-registration of biplane 2D-DSA whole frames into CBCTA, for which the routine acquisition of both subtracted and unsubtracted CBCTA axial images for ordinary diagnostic purposes is an indispensable prerequisite for successful image fusion and further widespread application. This frameless integration of the 2D/3D angiogram would dramatically enhance both the frame-based and frameless SRS workflow and circumstances by allowing users to forward SRS planning well in advance before SRS, along with the omission of invasive angiography on the day of SRS, and would broaden the implementation of frameless SRS. Furthermore, the comprehensive alternating interactive review of the 2D/3D integrated angiogram leads to a more in-depth quasi-4D understanding of the affected angioarchitectures compared with the separate viewing of each image.

Target localization accuracy in frame-based stereotactic radiosurgery: Comparison between MR-only and MR/CT co-registration approaches.

PurposeIn frame‐based Gamma Knife (GK) stereotactic radiosurgery two treatment planning workflows are commonly employed; one based solely on magnetic resonance (MR) images and the other based on magnetic resonance/computed tomography (MR/CT) co‐registered images. In both workflows, target localization accuracy (TLA) can be deteriorated due to MR‐related geometric distortions and/or MR/CT co‐registration uncertainties. In this study, the overall TLA following both clinical workflows is evaluated for cases of multiple brain metastases.MethodsA polymer gel‐filled head phantom, having the Leksell stereotactic headframe attached, was CT‐imaged and irradiated by a GK Perfexion unit. A total of 26 4‐mm shots were delivered at 26 locations directly defined in the Leksell stereotactic space (LSS), inducing adequate contrast in corresponding T2‐weighted (T2w) MR images. Prescribed shot coordinates served as reference locations. An additional MR scan was acquired to implement the “mean image” distortion correction technique. The TLA for each workflow was assessed by comparing the radiation‐induced target locations, identified in MR images, with corresponding reference locations. Using T1w MR and CT images of 15 patients (totaling 81 lesions), TLA in clinical cases was similarly assessed, considering MR‐corrected data as reference. For the MR/CT workflow, both global and region of interest (ROI)‐based MR/CT registration approaches were studied.ResultsIn phantom measurements, the MR‐corrected workflow demonstrated unsurpassed TLA (median offset of 0.2 mm) which deteriorated for MR‐only and MR/CT workflows (median offsets of 0.8 and 0.6 mm, respectively). In real‐patient cases, the MR‐only workflow resulted in offsets that exhibit a significant positive correlation with the distance from the MR isocenter, reaching 1.1 mm (median 0.6 mm). Comparable results were obtained for the MR/CT‐global workflow, although a maximum offset of 1.4 mm was detected. TLA was improved with the MR/CT‐ROI workflow resulting in median/maximum offsets of 0.4 mm/1.1 mm.ConclusionsSubpixel TLA is achievable in all workflows. For the MR/CT workflow, a ROI‐based MR/CT co‐registration approach could considerably increase TLA and should be preferred instead of a global registration.

Feasibility Study of Stereotactic Radiosurgery Treatment of Glomus Jugulare Tumors via HyperArc VMAT.

This study aims to report on the clinical validation and feasibility of utilizing a novel fully automated treatment planning and delivery system, HyperArc VMAT stereotactic radiosurgery (SRS) for glomus jugulare tumors (GJT). Independent dose verification of the HyperArc module via the MD Anderson's SRS head phantom irradiation and credentialing results showed compliance with the SRS treatment requirements per IROC MD Anderson's standard. Following the Alliance clinical trial, AAPM, RTOG protocols, and QUANTEC requirements, utilizing selected three-partial arc geometry of HyperArc module on TrueBeam Linac with 6MV-FFF beam, GJT SRS plans were generated for nine previously treated Gamma Knife (GK) radiosurgery patients using advanced Acuros-based algorithm to account for tissue inhomogeneity corrections and frameless immobilization with Q-fix mask and Encompass device insert. HyperArc VMAT produced highly conformal SRS dose distributions to GJT, a steep dose gradient around the GJT, and spared adjacent critical organs including the spinal cord (< 3.0 Gy). Due to faster patient setup and less MLC modulation through the target (average beam-on time, 6.2 minutes), the HyperArc VMAT plan can deliver a single high-dose of 18 Gy to the GJT in less than 15 minutes overall treatment time, significantly improving patient comfort and clinic workflow. Pretreatment portal dosimetry quality assurance results and independent dose verification via Monte Carlo-based physics second check met our clinical SRS protocol's requirements for treatment. Due to the highly conformal dose distribution, rapid dose fall-off, excellent sparing of adjacent critical organs, and highly precise and accurate treatment, clinical implementation of frameless HyperArc VMAT for GJT patients who may not have access to nor tolerate frame-based GK SRS treatment are underway.

Radiation Dose Rate, Biologically Effective Dose, and Tumor Characteristics on Local Control and Toxicity After Radiosurgery for Acoustic Neuromas

To evaluate the relationships between calibration dose rate, calculated biologically effective dose (BED), and clinical factors and tumor control after stereotactic radiosurgery (SRS) for acoustic neuroma. We performed a retrospective study of all patients with acoustic neuromas treated with frame-based cobalt-60 SRS at a single institution between 2005 and 2019. The calibration dose rate and cobalt-60 half-life were used to calculate the nominal dose rate during treatment. An SRS-specific monoexponential model accounting for treatment time per lesion was used to estimate BED. The study included 607 patients with 612 acoustic neuromas. Median follow-up was 5.0 years. There was no association between dose rate or BED with local failure (LF), radiologic edema, or symptomatic edema. Cystic tumors (adjusted hazard ratio 0.26, P= 0.028) were associated with lower LF, while use of SRS as salvage treatment for growing tumors (adjusted hazard ratio 4.9, P < 0.0001) was associated with higher LF. LF occurred more frequently in larger-diameter tumors, while radiologic or symptomatic edema occurred more frequently in larger-volume tumors. Radiosurgery dose rate and BED were not associated with tumor control or radiologic or symptomatic edema. Salvage SRS and larger tumors were associated with a higher LF rate, while cystic tumors were associated with a lower LF rate. Patients with larger tumors should be counseled appropriately about potential side effects and when to seek follow-up care.

Frameless Stereotactic Radiosurgery With Linear Accelerator (LINAC)-Based Technology for Brain Metastases: Outcomes Analysis in 141 Patients.

ObjectivesBrain metastases (BM) are the most common intracranial tumors in adults. Surgery and frame-based stereotactic radiosurgery (SRS) are well-described treatment options. Frameless SRS is an emerging BM treatment option offering fewer side effects. The aim of this study was to describe the therapeutic outcomes and toxicity of frameless SRS with linear accelerator (LINAC)-based technology for BM treatment in our institution.Materials and methodsWe performed a retrospective study including all adult patients treated with frameless SRS with LINAC-based technology for BM between October 2010 and July 2016. Patients were followed routinely with MRI scans at three-month intervals. Primary endpoints were progression-free survival, local control, overall survival, and toxicity related to the treatment. All survival times were computed with the Kaplan-Meier method. All cumulative incidences were computed using competing risk analyses.ResultsA total of 194 metastatic lesions in 141 patients were treated in a 69-month interval. At the time of analysis, 33 patients were still alive, with a median follow-up time of 25.1 months. The overall median survival was 8.7 months. The median progression-free survival was 5.3 months. Local recurrence as a first event was 25% and 38% at one and two years, respectively, while distant brain recurrence as a first event was 18% and 21%. Death before any brain event occurred in 31% of patients. The cumulative incidence of radiation necrosis as a first brain event was 2% at one and two years.ConclusionsThe treatment of BM with LINAC-based frameless SRS in our institution had an overall and progression-free survival comparable with the literature for frameless SRS and for conventional frame-based SRS while being less invasive and more comfortable for the patient. In our study, frameless SRS with LINAC technology seems to be safe for BM treatment with minimal rates of radiation necrosis.

Feasibility and potential advantages using VMAT in SRS metastasis treatments.

Utilization of stereotactic radiosurgery (SRS) for brain metastases (BM) has become the technique of choice as opposed to whole brain radiation therapy (WBRT). The aim of this work is to evaluate the feasibility and potential benefits in terms of normal tissue (NT) and dose escalation of volumetric modulated arc therapy (VMAT) in SRS metastasis treatment. A VMAT optimization procedure has therefore been developed for internal dose scaling which minimizes planner dependence. Five patient-plans incorporating treatment with frame-based SRS with dynamic conformal arc technique (DA) were re-planned for VMAT. The lesions selected were between 4-6 cm3. The same geometry used in the DA plans was maintained for the VMAT cases. A VMAT planning procedure was performed attempting to scale the dose in inner auxiliary volumes, and to explore the potential for dose scaling with this technique. Comparison of dose-volume histogram (DVH) parameters were obtained. VMAT allows a superior NT sparing plus conformity and dose scaling using the auxiliary volumes. The VMAT results were significantly superior in NT sparing, improving both the V10 and V12 values in all cases, with a 2-3 cm3 saving. In addition, VMAT improves the dose coverage D95 by about 0.5 Gy. The objective of dose escalation was achieved with VMAT with an increment of the Dmean and the Dmedian of about 2 Gy. This work shows a benefit of VMAT in SRS treatment with significant NT sparing. A VMAT optimization procedure, based on auxiliary inner volumes, has been developed, enabling internal dose escalation.

Frame-Based and Mask-Based Stereotactic Radiosurgery: The Patient Experience, Compared

Introduction: Noninvasive frameless modalities have become increasingly utilized for stereotactic radiosurgery (SRS) for benign and malignant pathologies. There is minimal comparison in the literature of frame-based (FB) and mask-based (MB) SRS. With the dual capabilities of the Elekta Gamma Knife® Icon™, we sought to compare patient perceptions of FB and MB SRS with respect to comfort and pain and to examine effects of lesion type on the patient experience of SRS. Methods: Over a 1-year period, patients who underwent single fraction, fractionated or hypofractionated FB or MB Gamma Knife SRS at our institution were given an 8-question survey about their experience with the procedure immediately after treatment was completed. Descriptive statistics were applied. Results: A total of 117 patients completed the survey with 65 FB and 52 MB SRS treatments. Mean pain for FB SRS (5.64 ± 2.55) was significantly greater than mean pain for MB SRS (0.92 ± 2.24; t₁₁₄ = 10.46, p < 0.001). Patient comfort during the procedure was also higher for those having MB SRS (p < 0.001). Mixed results were obtained when investigating if benign versus malignant diagnosis affected patient experience of SRS. For the purposes of this study, malignant diagnoses were almost entirely metastatic lesions. Diagnosis played no role on pain levels when all patients were analyzed together. The treatment technique had no effect on patient comfort in patients with benign diagnoses, while patients with malignant diagnoses treated with MB SRS were more likely to be comfortable (p < 0.001). Among patient’s receiving FB treatments, diagnosis played no role on patient comfort. When only MB treatments were analyzed, patients were more likely to be comfortable if they had a malignant lesion (p < 0.01). Conclusions: Patients treated with MB SRS experience the procedure as more comfortable and less painful compared to those treated using a FB modality. Overall, this difference was not affected by a benign versus a malignant diagnosis and the treatment type is more indicative of the patient experience during SRS. A more homogenous sample between modalities and diagnoses and further follow-up with the patient’s input on their experience would be beneficial.

RADT-19. EFFECTS OF RADIATION DOSE-RATE AND TUMOR CHARACTERISTICS ON LOCAL CONTROL AND TOXICITY AFTER RADIOSURGERY FOR ACOUSTIC NEUROMAS

Abstract INTRODUCTION The effect of stereotactic radiosurgery (SRS) dose-rate on tumor control for acoustic neuroma (AN, or vestibular schwannoma) is unclear. METHODS This was a retrospective study of all patients treated for AN with frame-based cobalt-60 SRS at the Toronto Western Hospital between 2005-2019. Dose rates on the day of SRS were calculated from the calibration dose-rate while accounting for the cobalt-60 half-life of 5.2713 years. Local failure was defined as continued tumor growth &amp;gt;36 months post-SRS, tumor resection for LF, or use of any repeat SRS for LF. Cumulative incidence of LF was reported after accounting for competing risks of death, on a per-lesion basis. Comparisons of actuarial LF were made using Gray’s test. Multivariable analysis of LF was performed using a proportional hazards model. RESULTS A total of 607 patients were treated for 617 acoustic neuromas. Median follow-up was 5.0 years. 158 tumors (26%) were cystic. 71 tumors (12%) had previous resection. Nine patients received 10-11 Gy due to large tumor size; all remaining patients received 12 Gy to approximately the 50% isodose line. Median dose rate was 2.4 Gy/min (range, 1.3-3.7). There was no association between dose rate and LF (≥ 2.4 Gy/min vs. &amp;lt; 2.4 Gy/min, 6.07% vs. 6.12% at 5-year follow-up, p = 0.75). The adjusted local failure-specific hazard ratio (HR) for dose rate (per Gy/min) was 1.2 (95% CI 0.69-2.1, p = 0.52). Patients with previous surgery had higher LF, with a HR of 3.6 (95% CI 1.7-7.8, p = 0.0012), after adjusting for presence of cysts (HR 0.27, p = 0.034) and maximum tumor diameter (HR 1.055 per cm, p = 0.071). CONCLUSIONS In a large cohort of patients with acoustic neuromas, radiosurgery dose-rate was not associated with tumor control. Previous resection was a strong risk factor for local failure after SRS.

Single-fraction Stereotactic Radiosurgery Outcomes for Brain Metastases with Frameless Gamma Knife ICON Radiosurgery: An Update

Traditionally, immobilization and localization of brain targets suitable for Gamma Knife Radiosurgery (GKRS) has been performed by application of a rigid pin-based frame to the patient’s skull. In 2015, The Leksell Gamma Knife ICON was introduced and provided the first frameless, noninvasive alternative to the stereotactic head frame. There is limited data on treatment outcomes for patients treated with single-fraction frameless stereotactic radiosurgery (SRS). We sought to evaluate local control of brain metastases (BM) among patients treated with single-fraction SRS using frameless versus frame-based immobilization. Prospectively enrolled consecutive patients with metastatic brain tumors treated with single-fraction frameless or frame-based GKRS between 2017 and 2020 were retrospectively reviewed in our institutional review board (IRB) approved database. We used chi-squared tests and t-tests to compare demographic and clinical characteristics by treatment modality. We then used Kaplan-Meier methods to compare the two treatment groups’ local control and survival, and evaluated the statistical significance of the differences by log rank test. Forty-one consecutive patients with 95 BM treated with single-fraction frameless SRS were compared to 33 consecutive patients with 104 BM treated with single-fraction framed SRS. There were 84 intact metastases and 11 postoperative cavities treated in the frameless SRS group and 98 intact metastases and 6 postoperative cavities treated in the frame SRS group. Median follow-up time was 10.5 months for frameless SRS and 7 months for framed SRS. There were no statistically significant differences in patient characteristics between frameless SRS and framed SRS including age, KPS, number of BM, presence of extra-cerebral metastases, and uncontrolled systemic disease. Patients who were treated with frameless SRS had more pre-treatment neurological symptoms (p = 0.03) and were more likely to have been treated with a tyrosine kinase inhibitor either concurrently or within 4 weeks of treatment (p = 0.005). On average, metastasis volume was larger in the frameless SRS group (1.28 cc) compared to frame-based SRS (0.76 cc) but this difference was not statistically significant. At 1 year, local control of BM treated with frameless SRS was 92% compared to 86% for framed SRS (p = 0.62). Actuarial overall survival was similar between the groups (p = 0.46). Single-fraction frameless SRS provides similar local control compared to frame-based SRS in the treatment of BM.

Novel Approach of Linear Accelerator-Based Stereotactic Radiosurgery in an Adult Patient With Brain Arteriovenous Malformation: A Case Report and Clinical Outcome

Stereotactic radiosurgery (SRS) is a proven strategy for treating the central nervous system arteriovenous malformation (AVM). We intend to present a case of cerebral AVM in an adult patient, successfully treated with a linear accelerator (LINAC) based SRS using simplified setup techniques and an advanced planning system. In the current scenario, frame-based SRS is the standard of care with LINAC. Recently, it has proven that even frameless SRS has similar results. In our case, we used a frameless SRS technique with similar results. While calculating the dose in radiotherapy planning, we used the Acuros™ algorithm, which has proven dosimetric advantages compared to the traditional AAA™ algorithm.

Assessment of unintended shifts during frame-based stereotactic radiosurgery using cone beam computed tomography image guidance.

To investigate the frequency, magnitude and possible causes of frame-shifts that may occur between treatment planning and treatment delivery when performing Gamma Knife radiosurgery with rigid frame-based immobilization. Differences between computed tomography (CT) framed fiducial stereotactic coordinate reference and cone beam computed tomography stereotactic coordinates after image registration were recorded for 49 frame-based GK radiosurgery cases performed using the Gamma Knife Icon. Parameters recorded include rotational shifts, translational shifts, and the GK-computed Maximum Shot Displacement (MSD) between the two stereotactic coordinate spaces. Other patient-specific parameters were collected and linear regression analysis was performed to evaluate predictors of increased displacement. The median values of rotational shifts were: pitch 0.14°, yaw 0.17°, and roll 0.13°. The median absolute values of translational shifts were: left-right 0.39mm, anteroposterior 0.14mm, and superior-inferior 0. 22mm. The median value of MSD was 0.71mm. Twelve cases (24.5%) had a MSD of greater than 1.0mm. Male gender was associated with increased MSD (p = 0.013) and translational shifts (root-mean-squared value, p = 0.017). Cases with large differences between right and left sided pin lengths were also associated with increased MSD (p = 0.011). The use of CBCT image guidance in frame-based GK radiosurgery allows unintended frame shifts to be identified and corrected. A significant fraction (24.5%) of patients had large enough shifts to result in a MSD of greater than 1.0mm. Male gender and eccentrically placed frames were associated with increased MSD, and particular care should be taken in these cases.

RTHP-03. FRAME-BASED AND MASKED STEREOTACTIC RADIOSURGERY: A PATIENT EXPERIENCE COMPARISON WITH THE GAMMA KNIFE ICON

Abstract INTRODUCTION Patients undergoing stereotactic radiosurgery (SRS) for intracranial pathology have two treatment options: frame-based (FB) versus masked (MB). There is sparse information on a patient’s experience between the two types and to what extent a patient’s diagnosis will predict their SRS experience. METHODS A retrospective analysis of patients who completed a questionnaire of their experience after SRS using the Gamma Knife Icon was completed. RESULTS Fifty-eight patients completed the questionnaire, 60% were FB and 40% MB. The average age was 63.3 + 15.3 years, 40% were male. Of the patients treated with a FB technique, 51% didn’t find SRS to be uncomfortable. Comparatively, 91% of MB patients didn’t find SRS to be uncomfortable. Patients who underwent FB treatment rated their pain of frame placement on a visual analog scale (VAS) 1–3, 24%, VAS 4–6, 46%, VAS 7–10, 30%. Eight patients answered that they didn’t tolerate the procedure as expected, most of which were treated using a FB method (87%). Compared to previous surgery or SRS, five patients found their experience of SRS wasn’t tolerable, while 93% of patients would consider repeat SRS. All patients treated felt adequately informed about the procedure. The patient experience of discomfort during SRS and their evaluation of pain during frame placement between patients treated for benign versus malignant lesions (discomfort: 59% vs. 22%, respectively and median VAS pain: 6 + 2.67, 4.5 + 1.99, respectively) determined a benign diagnosis had more discomfort during SRS compared to a malignant diagnosis. Pain during frame placement was similar for both diagnoses. CONCLUSION Patients experienced frame-based SRS as more uncomfortable than mask-based treatment. Benign pathologies appeared to have more discomfort compared to malignant pathologies. All patients of both techniques felt adequately informed about their procedure.

Determination of Stereotactic Shifts for Frame-Based Stereotactic Radiosurgery Using Cone-Beam Computed Tomography Image Guidance

Determination of Stereotactic Shifts for Frame-Based Stereotactic Radiosurgery Using Cone-Beam Computed Tomography Image Guidance

RADI-36. FRAME-BASED VERSUS FRAMELESS GAMMA KNIFE RADIOSURGERY FOR BRAIN METASTASES

INTRODUCTION: Brain metastases occur in 10 to 40% of cancer patients. In an effort to avoid the neurocognitive toxicities of whole brain radiation therapy, stereotactic radiosurgery (SRS) has become the preferred treatment option for most brain metastases. Many cancer patients will require several rounds of SRS during the course of their disease. Frame-based radiosurgery causes physical discomfort with each treatment session. We present our experience with frameless Gamma Knife radiosurgery (GKRS) and compare the clinical outcomes to frame-based treatments in the same patient cohort. METHODS: We evaluated all patients with brain metastases who underwent both frame-based and frameless SRS, using the Gamma Knife ICON, between January 2017 and November 2018. 11 patients with 110 unique lesions were included in this analysis. Clinical outcomes, including local control, were compared between the two treatment modalities. RESULTS: Mean patient age was 60.0 (range: 41 – 76) years. Median follow-up was 7.9 (range: 0 – 22.1) months. Median number of metastases treated was 4 (range: 1 – 9) per frame-based treatment and 3 (range: 1 – 10) per frameless treatment. Median number of frame-based and frameless procedures, per patient, was 1 (range: 1 – 3) and 1 (range: 1 – 2), respectively. Median tumor volume was 0.06 (range: 0.01 – 11.49) cm3 in the frame-based treatments and 0.14 (range: 0.01 – 4.22) cm3 in the frameless treatments. Median margin dose was 18 Gy for both the frame-based and frameless treatments. Local control was 86.5 and 91.5% at 6 and 9 months post-treatment, respectively in the frame-based treatments and 82.8 and 87.5% at 6 and 9 months post-treatment, respectively in the frameless treatments. CONCLUSIONS: Frameless GKRS results in similar rates of local control compared to frame-based GKRS. This treatment option should be considered in patients undergoing GKRS, as it balances clinical outcomes with patient comfort.

Frame-based radiosurgery of multiple metastases using single-isocenter volumetric modulated arc therapy technique.

Single‐isocenter volumetric modulated arc therapy (VMAT) technique can provide stereotactic radiosurgery (SRS) treatment with improved delivery efficiency for treating multiple metastases. Nevertheless, planning is time consuming and verification of frame‐based SRS setup, especially at noncoplanar angles, can be challenging. We report on a single‐isocenter VMAT technique with a special focus on improving treatment workflow and delivery verification to exploit the minimized patient motion of the frame‐based SRS. We developed protocols for preplanning and verification for VMAT and evaluated them for ten patient cases. Preplans based on MRI were used to generate comparable treatment plans using CT taken on the day of treatment after frame placement. Target positioning accuracy was evaluated by stereoscopic in‐room kV imaging. Dosimetric accuracy of the noncoplanar plan delivery was validated using measurement‐guided 3D dose reconstruction as well as film‐based end‐to‐end test with a Rando phantom. Average absolute differences of homogeneity indices, conformity indices, and V12Gy between MR preplans and CT‐based plans were within 5%. In‐room imaging positioning accuracy of 0.4 mm was verified to be independent of the distance to the isocenter. For treatment verification, average local and global passing rates of the 3D gamma (1 mm, 3%) were 86% and 99%, respectively. D99 values were matched within 5% for individual target structures (>0.5 cc). Additional film analysis confirmed dosimetric accuracy for small targets that had large verification errors in the 3D dose reconstruction. Our results suggest that the advantages of frame‐based SRS and noncoplanar single‐isocenter VMAT technique can be combined for efficient and accurate treatment of patients with multiple metastases.