Prior Radiosurgery Research Articles

303 Frameless Angiography-Based Gamma Knife Stereotactic Radiosurgery for Cerebral Arteriovenous Malformations

INTRODUCTION: Traditional GammaKnife radiosurgery (GKRS) of brain arteriovenous malformations (AVMs) using digital subtraction angiography requires head immobilization using a stereotactic frame. METHODS: This is a retrospective review of unruptured AVM patients who underwent frameless GKRS. Thin-cut magnetic resonance imaging and 3-dimensional DSA were obtained without a stereotactic frame for all patients. The imaging studies were merged for contouring of the AVM nidus. During GKRS treatment, patients were immobilized using an individually molded thermoplastic mask. RESULTS: Thirty-one patients were included in the analysis. The median age is 45.0 years (IQR 28.0-55.0). The median nidus size is 3.0 cm (IQR 2.0-3.4). One patient had a Spetzler-Martin grade I, 11 had a grade II, 11 had a grade III, 6 had a grade IV, and 2 had a grade IV AVM. Eleven patients underwent pre-radiosurgical embolization, two patients had previous microsurgical resection, and one patient had prior radiosurgery. The median administered dose was 20 Gy (IQR 18.0-21.0). Twenty-three patients were treated in a single fraction, 6 in 3 fractions, and two patients received 5 fractions. All patients completed their treatment with the planned radiation dose without complications. CONCLUSIONS: This is the first study that integrates digital subtraction angiography in the treatment planning of brain AVMs using GKRS without utilizing a stereotactic head frame. Frameless GKRS provides numerous advantages over frame-based techniques including improved patient experience, the capability of fractionation, thus, expanding the eligibility of more AVMs for radiosurgery, while maintaining high spatial resolution of the AVM using angiography data.

Outcomes of Brain Metastases Managed with Resection and Aggressive Reirradiation after Initial Radiosurgery Failure

<h3>Purpose/Objective(s)</h3> To evaluate local control, overall survival, and toxicity profiles in patients with brain metastases aggressively treated with initial radiation followed by resection and aggressive re-irradiation upon pathological confirmation of failure of prior radiosurgery treatment. <h3>Materials/Methods</h3> A retrospective chart review identified 55 lesions in 51 patients that were initially treated with stereotactic radiosurgery (SRS), then demonstrated evidence of recurrence with pathologic confirmation and underwent high dose re-irradiation either with radiosurgery (n=43, 78.2%) or intracavitary brachytherapy with Cesium-131 seeds (n=12, 21.8%). Toxicity was measured by: steroids initiated or increased within 3 months, imaging evidence of treatment effect vs disease progression at any time point, further intervention for local recurrence or necrosis, and any grade 3/4 neurologic events. Local control (with failure defined by sustained progression on imaging or pathologic confirmation of tumor) was measured from time of re-treatment. Overall survival (OS) and local control were evaluated using the Kaplan-Meier method. <h3>Results</h3> Median follow-up from re-irradiation was 32.5 months (IQR 18-45 months). The majority of cohort patients were female (66.7 %), with median age at first SRS of 56.3 years old. Primary histology was non-small cell lung cancer (NSCLC) in 19 cases (37.2%) and breast cancer in 12 cases (23.53%). Ten individuals had previous WBRT (19.5%) prior to initial stereotactic therapy. The most common dose fractionation for initial SRS was 18 Gy x 1 fraction (18 lesions, 32.7%), and the most common dose fractionation for repeat SRS was 8 Gy in 3 fractions (15 lesions, 27.3%). Twenty-five lesions (45.4%) required use of steroids after re-irradiation. Among all patients, 21.8% experienced evidence of grade 3 or 4 neurotoxicity. There was no statistically significant difference in the rate of steroid use or grade 3-4 neurotoxicity between lesions re-irradiated with SRS vs. brachytherapy (25.6% vs. 8.33% grade 3-4 neurotoxicity; p=0.201 and 51.2% vs 25% steroid use; p=0.108). Forty percent had imaging changes of possible pseudoprogression, radiation necrosis, or true progression. Of patients with imaging changes, 27% (10.9% of all treated patients) were confirmed necrosis by pathology. Median OS was 14.1 months (95% CI 7.63 – 24.3). The 2-year OS was 52% (95% CI 39, 69.3%) and 2-year local control rate was 79.5% (95% CI 61.7, 68.3%). <h3>Conclusion</h3> Aggressive re-irradiation with radiosurgery or brachytherapy after resection for pathologically confirmed progression after prior radiosurgery is appropriately effective and demonstrate similar toxicity profiles.

Frameless Angiography–Based Gamma Knife Stereotactic Radiosurgery for Cerebral Arteriovenous Malformations: A Proof-of-Concept Study

Traditional Gamma Knife radiosurgery (GKRS) of brain arteriovenous malformations (AVMs) using digital subtraction angiography (DSA) requires head immobilization using a stereotactic frame. We describe our protocol of frameless GKRS using DSA while maintaining high spatial resolution for precision. This study is a retrospective review of patients with unruptured AVMs who underwent frameless GKRS. Magnetic resonance imaging and 3-dimensional DSA were obtained without a stereotactic frame for all patients. The imaging studies were merged for contouring of the AVM nidus. During GKRS treatment, patients were immobilized using an individually molded thermoplastic mask. Thirty-one patients were included in the analysis. The median age is 45.0years (interquartile range [IQR]: 28.0-55.0). The median nidus size is 3.0cm (IQR: 2.0-3.4). One patient had a Spetzler-Martin grade I, 11 had a grade II, 11 had a grade III, 6 had a grade IV, and 2 had a grade V AVM. Eleven patients underwent preradiosurgical embolization, 3 patients had previous microsurgical resection and/or embolization, and 1 patient had prior radiosurgery. The median administered dose was 20Gy (IQR: 18.0-21.0). All patients completed their treatment with the planned radiation dose without complications. This is the first study that integrates DSA in the treatment planning of brain AVMs using GKRS without utilizing a stereotactic head frame. Frameless GKRS provides numerous advantages over frame-based techniques including improved patient experience and the capability of fractionation and thus expanding the eligibility of more AVMs for radiosurgery, while maintaining high spatial resolution of the AVM using angiography data.

Impact of APOE Genotype on Neurocognitive Outcomes in Hippocampal Avoidance Whole Brain Radiotherapy for Brain Metastases: A Secondary Analysis of Phase II Blinded Randomized Trial

Apolipoprotein E (APOE) polymorphism is a well-known risk associated with Alzheimer's disease. Its role in neurocognition decline after whole brain radiotherapy (WBRT) for brain metastases is not well-investigated. The present secondary analysis of a prospective blinded randomized controlled phase II trial aimed to evaluate the impact of APOE genotypes upon neurocognitive outcomes after WBRT with or without hippocampal avoidance.Adult patients with brain metastases were stratified by prior radiosurgery and randomized to hippocampal avoidant conformal WBRT versus conformal WBRT without hippocampal avoidance to 30 Gy in 10 fractions from March 2015 to November 2018. Memantine was not used during or after WBRT. Standardized neurocognitive test battery (Hopkins Verbal Learning Test-Revised [HVLT-R], Trail Making Test), was performed at baseline, 1, 2, 4, 6, and every 3 months up to two years by trained independent health professionals. Both clinical trial participants and examiners were blinded to the treatment group assignment. APOE alleles were determined by the genome-wide genotyping. The association between APOE genotypes and neurocognitive outcomes was analyzed by general linear model. The role of APOE genotypes on the effect of hippocampal avoidance during WBRT was also evaluated. Factorial ANOVA was used to assess the independent factors associated with neurocognitive outcomes.Among 65 analyzable patients, APOE genotyping was available for 64.6% (n = 42) of patients. The most frequent APOE allele was ε3 homozygote (ε3/ε3, n = 24), followed by ε2 carrier (ε2/ε3, n = 11) and ε4 carrier (ε4/ε3, n = 7). No differences in baseline characteristics and cognitions between patients of different APOE genotypes. At 6-month, patients carrying APOE ε2 and ε4 allele had the best and worst preservation in HVLT-R total recall (mean difference, ε2: +3.18 versus ε4: -3.20, P = 0.008), and delayed recall (mean difference, ε2 carrier: +0.46 versus ε4 carrier: -2.40, P = 0.03), respectively. The effect of preservation in 6-month memory score is the strongest in the APOE ε2 carriers followed by the APOE ε3 homozygotes, and the least in the APEO ε4 carriers in order (P = 0.028). Only patients of APOE ε3 homozygotes showed improved preservation in late memory score by hippocampal avoidant WBRT at 6-month (mean difference, hippocampal avoidant: +3.67 versus conformal: -3.18, P = 0.037) and beyond. APOE genotyping was independent of age and hippocampal avoidance to be associated with the preservation of 6-month HVLT-R total recall (P = 0.042), and HVLT-R delayed recall (P = 0.032).The APOE genotype is associated with the risk of memory decline after WBRT. Specifically, APOE ε2 carriers exhibited better while ε4 carriers showed worse perpetuation in verbal memory function after WBRT. APOE ε3 homozygotes but not APOE ε2 or ε4 carriers benefit late memory preservation by hippocampal avoidant WBRT for brain metastases.

Salvage Resection and Intracranial Cesium-131 Brachytherapy for Brain Tumors

Management of progressive brain tumors following high dose radiotherapy is controversial. In select cases, surgical resection can provide rapid relief of regional mass effect and edema, and highly focal adjuvant re-irradiation can be administered in the form of brachytherapy. Permanent low-dose rate cesium-131 brachytherapy may offer dosimetric and radiobiologic advantages over other isotopes. The purpose of this study was to examine the safety and efficacy of intracranial cesium-131 brachytherapy after surgical resection in a heavily pre-treated patient cohort.A retrospective chart review was conducted of all patients treated with intraoperative intracranial cesium-131 brachytherapy from an institutional database. Treatment consisted of maximal safe resection followed by implantation of suture-stranded cesium-131 seeds, maintaining approximately 10mm spacing between seeds, with a planned target dose of 80 Gy to 5mm depth. Local failure was defined as recurrence in or contacting the resection cavity after salvage resection and brachytherapy. Regional failure was defined as recurrence within 10mm of the resection cavity. Recurrence was defined as a new lesion or growth of ≥25% in any axial dimension on interval MRI. Toxicity was collected based on CTCAE 4.0.A total of 35 patients with a median imaging follow up of 17.0 months (interquartile range [IQR] 9.7-25.9) underwent 41 consecutive cesium-131 implants between 2016 and 2020. 20 patients (59%; N = 22 implants) were treated for recurrent brain metastasis, 12 patients (34%; N = 16 implants) were treated for recurrent atypical (N = 8) or anaplastic meningioma (N = 4), and 3 patients (9%) were treated for recurrent glioma (N = 2) or hemangiopericytoma (N = 1). A majority of lesions had received prior surgery (N = 28, 66.7%, range 0-3 prior surgeries) and 34 patients had received prior high dose radiation. 34 of 41 (82.9%) tumors had received prior radiosurgery, and 12 (29.2%) had undergone prior external beam radiation (range 50-60 Gy). 17 of 41 lesions (41.5%) had radiologic evidence of adverse radiation/treatment effect (ARE) prior to salvage therapy. Median tumor size was 3.0cm (IQR 2.3-3.7). Overall actuarial local/loco-regional control at 1-year was 91.6%/84.7% (89.8%/88.9% for metastases and 100%/82.5% for meningiomas). Crude loco-regional control was 86.3% for metastases, 75% for meningiomas, and 66.7% for other lesions. Symptomatic ARE following treatment was observed in 9.8% (N = 4) resection cavities. The surgical complication rate was 14.6% (N = 6 total, N = 3 [7.3%] grade 3-5) including 1 peri-operative death.Cesium-131 brachytherapy in this heavily pre-treated cohort resulted in good local control and an acceptable rate of symptomatic adverse radiation effect and toxicity and may be a reasonable treatment option for this select population.W.C. Chen: None. M. Lafreniere: None. C. Phuong: None. M. Lometti: None. O. Morin: None. B.P. Ziemer: None. H. Vasudevan: Research Grant; Children's Tumor Foundation. Patent/License Fees/Copyright; Genentech, Eli Lilly. S. Hervey-Jumper: None. P.V. Theodosopoulos: None. S. Magill: None. S.E. Fogh: Independent Contractor; Accuray. J.L. Nakamura: None. L. Boreta: None. P.K. Sneed: None. M.W. McDermott: Chair; Miami Baptist. D. Raleigh: None. S.E. Braunstein: Advisory Board; Radiation Oncology Questions, LLC.

RADI-22. Toxicity and local control outcomes for brain metastases managed with resection and aggressive reirradiation after initial radiosurgery failure

ObjectivesTo describe toxicity and tumor outcome after resection and aggressive re-irradiation (stereotactic radiosurgery(SRS) or brachytherapy) of brain metastasis that have pathologically confirmed recurrence after prior radiosurgery.MethodsA retrospective chart review identified 40 lesions in 35 patients that were initially treated with SRS, then demonstrated evidence of recurrence with pathologic confirmation and underwent re-irradiation either with radiosurgery (n=28, 70%) or intracavitary brachytherapy with Cesium-131 seeds (n=12, 30%). Toxicity was measured by: steroids initiated or increased within 3 months, imaging evidence of treatment effect vs disease progression at any time point, further intervention for local recurrence or necrosis, and any grade 3/4 neurologic events. Local control (with failure defined by sustained progression on imaging or pathologic confirmation of tumor) was measured from time of retreatment.ResultsMedian follow-up from time of re-irradiation was 11.8 months (range 1 – 89.7 months). Dose for repeat radiosurgery was 18–25 Gy in 1–5 fractions, and brachytherapy dose was 55–65 Gy at 5 mm depth. Twelve lesions subsequently had imaging evidence of radionecrosis vs. progression. Of these, eight underwent repeat resection with pathology demonstrating radiation necrosis in five patients (n=4 with SRS, n=1 with brachy) and tumor recurrence in 3 (n=2 with brachy, and n=1 with SRS). Toxicities included: Steroids, 14(35%); imaging progression/necrosis 12(30%); grade 3/4 event, 3(20%); and surgically confirmed radionecrosis 5(12.5%). Local control of retreated lesions at 6 months is 85.5%, and at 12 months is 79.3%, OS at 1 year is 52.5% and at 2 years 46.6%. Local control at one year for repeat stereotactic treatment was 82.9% and for Cs131 brachytherapy was 80.8%ConclusionsAggressive re-irradiation after resection for pathologic confirmation appears to be appropriately safe and effective for the majority of patients after local failure of initial radiosurgery.

14. DELAYED MRI RESPONSE TO LITT IN PATIENTS UNDERGOING IMMUNOTHERAPY

Laser interstitial thermal therapy (LITT) is an effective treatment for regrowing lesions after previous radiosurgery to brain metastases, typically resulting in decreased perilesional edema within weeks followed by delayed reduction in lesion size. We have anecdotally observed that patients on immunotherapy (IT) at time of LITT may exhibit a delayed edema resolution response to laser ablation. Post-operative imaging for cases of LITT, performed by the senior author from June 2012-July 2019, for regrowing lesions after prior radiosurgery for brain metastases were retrospectively reviewed. The IT group was defined as any patient receiving IT treatment within 3 months of LITT. Post-operative MRIs obtained at serial time points after surgery (2 weeks, 6 weeks, 3 months, 6 months, and 12 months) were reviewed for treatment response to LITT, defined as change in surrounding edema on T2 FLAIR and change of lesion size on T1-weighted post-contrast images. Out of 60 ablated lesions, 22 were in the IT and 38 were in the non-IT groups. There were no differences in distribution of original cancer pathology (IT: 9 melanoma, 8 lung, 5 other, non-IT: 6 melanoma, 20 lung, 12 other; p>0.05). Time to lesion size response on T1-weighted post-contrast MRI neared but did not reach statistical significance between the IT and non-IT groups: median 3.0 versus 2.25 months (HR 1.5, 0.8–2.5, 95% CI, p=0.08), respectively. However, time to reduction of perilesional edema on T2-weighted MRI was significantly longer in the IT group, compared to the non-IT group: median 2.25 versus 1.5 months (HR 1.5, 0.9–2.5, 95% CI, p=0.04), respectively. These data suggest that IT around the time of LITT may lead to delayed edema reduction on MRI after LITT. We hypothesize IT may enhance normal immune-mediated mechanisms thus increasing perilesional inflammation after LITT. Further studies are needed to corroborate our observations and explore the underlying pathophysiology.

Risk factors for wound-related complications after microvascular decompression.

Retrosigmoid craniotomy for microvascular decompression (MVD) has been traditionally performed via craniectomy. Various closure techniques have been described, yet factors associated with wound-related complications remain undetermined. Accordingly, herein, we sought to identify risk factors associated with wound-related complications after such procedures. An institutional retrospective case-control study was performed; outcomes of interest were cerebrospinal fluid (CSF) leak, wound dehiscence, wound infection, and pseudomeningocele. Univariate analysis was performed using Wilcoxon rank sum test for non-parametric continuous outcomes and chi-square test for categorical outcomes. Multivariate logistic regression was performed on binomial outcome variables. The study population included 197 patients who underwent MVD for trigeminal neuralgia (83.2%), hemifacial spasm (12.2%), vestibular nerve section (3.0%), and glossopharyngeal neuralgia (1.5%). The overall wound-related complication rate was 14.2% (n= 28), including twelve patients (6.1%) with CSF leak, ten patients (5.1%) with wound infection, ten patients (5.1%) with pseudomeningocele, and nine (4.6%) patients with wound dehiscence. Using multivariate logistic regression, preoperative anemia and current tobacco use were associated with significantly higher rates of complications (OR 6.01 and 4.58, respectively; p< 0.05), including CSF leak (OR 12.83 and 12.40, respectively, p< 0.05). Of note, use of synthetic bone substitute for cranioplasty was associated with a significantly lower rate of complications (OR 0.13, p< 0.01). Preoperative anemia and current tobacco use significantly increased, while synthetic bone substitute cranioplasty significantly decreased, odds of wound-related complications, the need for treatment, and CSF leaks. Additionally, higher BMI, longer operative duration, and prior radiosurgery may increase risk for wound-related complications.

RADI-19. EVALUATION OF BRAIN METASTASIS LOCAL CONTROL POST RADIOSURGERY VIA MACHINE LEARNING AND RADIOMICS

Stereotactic radiosurgery can be used to treat multiple, surgically inaccessible, metastatic brain lesions in a single, minimally invasive outpatient procedure. For brain metastasis, stereotactic radiosurgery can provide excellent local control depending on the robustness of the treatment plan. Previous studies have been performed correlating key radiation planning factors to higher local control probability such as tumor size and maximum dose. However, a separate non-inferiority study demonstrated that higher prescription isodose lines (in excess of 70% or higher) did not correlate to local failure. The previous works were limited to shallow feature levels regarding only the dicom plan information and lacked a predictive model. In order to address these conflicting conclusions and to support clinical decision making, we propose a radiosurgery informatics pipeline to support testing these hypotheses with observational data. First, a multidisciplinary team generated a mind-map of relevant information to inform database design. Portions of this mind-map were implemented in a relational database system (PorstgreSQL), and populated with information from 1024 patients treated for brain metastasis via stereotactic radiosurgery. Clinical information were derived from curated databases and the array of intervention variables were mined from the DICOM RT plans, structure sets, images and dose via MATLAB scripts. These factors include, but are not limited to, radiation dosimetry, prior whole brain radiation, radiomic imaging features, prior radiosurgery status, and physician determined local control status. From this pipeline, we plan to use a multi-level feature-based supervised machine learning approach that will be created via boosting to predict local control in patients using local failure timing, or lack thereof, provided by physician. To control for local failure observer bias, an unsupervised machine learning model via random trees will be created to predict clusters of patient parameters with similar local control rates.

Magnetic Resonance-Guided Laser-Induced Thermal Therapy for the Treatment of Progressive Enhancing Inflammatory Reactions Following Stereotactic Radiosurgery, or PEIRs, for Metastatic Brain Disease.

In patients who have previously undergone maximum radiation for metastatic brain tumors, a progressive enhancing inflammatory reaction (PEIR) that represents either tumor recurrence or radiation necrosis, or a combination of both, can occur. Magnetic resonance-guided laser-induced thermal therapy (LITT) offers a minimally invasive treatment option for this problem. To report our single-center experience using LITT to treat PEIRs after radiosurgery for brain metastases. Patients with progressive, enhancing reactions at the site of prior radiosurgery for metastatic brain tumors and who had a Karnofsky performance status of≥70 were eligible for LITT. The primary endpoint was local control. Secondary end points included dexamethasone use and procedure-related complications. Between 2010 and 2017, 59 patients who underwent 74 LITT procedures for 74 PEIRs met inclusion criteria. The mean pre-LITT PEIR size measured 3.4±0.4 cm3. At a median follow-up of 44.6 wk post-LITT, the local control rate was 83.1%. Most patients were weaned off steroids post-LITT. Patients experiencing a post-LITT complication were more likely to remain on steroids indefinitely. The rate of new permanent neurological deficit was 3.4%. LITT is an effective treatment for local control of PEIRs after radiosurgery for metastatic brain disease. When possible, we recommend offering LITT once PEIRs are identified and prior to the initiation of high-dose steroids for symptom relief.

Stereotactic Radiosurgery in Recurrent Brain Metastases After Prior Radiosurgery: A Case Report and Review of Literature

ABSTRACTPreviously, all brain metastasis has been treated with whole brain radiotherapy and the survival is poor. Recently, the development of stereotactic radiosurgery (SRS) provides comparable efficacy with low toxicity, and in several cases have a better survival compared to historical data. We conducted a case review in brain metastasis, which has been treated with SRS previously and experienced distant brain recurrence, then re-treated with SRS.ABSTRAKDahulu, semua metastasis otak ditangani dengan modalitas radiasi seluruh otak dan memiliki kesintasan yang tidak terlalu baik. Saat ini berkembang modalitas stereotactic radiosurgery (SRS). SRS memberikan efektivitas yang sebanding dengan toksisitas yang rendah dan pada beberapa kasus memiliki kesintasan yang lebih baik dibandingkandata sebelumnya. Berikut adalah tinjauan kasus metastasis otak dengan penanganan SRS sebelumnya dan mengalami kekambuhan di lokasi lain pada otak, kemudian ditatalaksana ulang dengan SRS.

152 Complications Associated with Transsphenoidal Pituitary Surgery

Abstract INTRODUCTION Pituitary adenomas (PAs) are benign neoplasms frequently encountered during workup for endocrinopathy, headache, or visual loss. Transsphenoidal surgery remains the mainstay approach for PA resection. We retrospectively assessed safety and complication rates associated with transsphenoidal PA resection. METHODS The USC Pituitary Center REDCap electronic database was used to identify 1171 consecutive patients who underwent microscopic (85%) or endoscopic (15%) transsphenoidal PA resection at Keck Hospital of USC between November 1992 - March 2017. A retrospective analysis of perioperative complications and patient/tumor risk factors was conducted. RESULTS &gt;There were 2 perioperative mortalities (0.2%) in this series. Additional surgical complications included cerebrospinal fluid leak (2.6%), new neurological deficit (1.3%), meningitis (1.0%), postoperative hematoma (1%), cranial nerve paresis (0.9%), hydrocephalus (0.7%), vision loss (0.6%), stroke (0.4%), vegetative state (0.1%) and carotid artery injury (0.1%). Perioperative medical complications included bacteremia/sepsis (0.5%), pneumonia (0.4%), myocardial infarction (0.3%), and DVT/PE (0.2%). Endocrine complications were the most frequent, including transient diabetes insipidus (4.5%), symptomatic hyponatremia (4.3%), permanent diabetes insipidus (0.3%), and new hypopituitarism (3.8%). There were no significant differences between microscopic versus endoscopic approaches with regard to overall complications (16.9% vs. 19.1%; P = 0.513) or major complications (5% vs. 4%; P = 0.601). Risk factors for major complications included: prior transsphenoidal surgery (8.5% versus 4.5%; P = 0.043), prior craniotomy (23.5% versus 4.5%; P = 0.001), prior radiosurgery (33.3% versus 4.5%, P = 0.007), presence of PA invasion on MRI (7.0% versus 2.4%; P = 0.001), and preoperative vision loss (8.8% versus 5.0%; P &lt; 0.001). CONCLUSION In one of the largest studies assessing complications associated with transsphenoidal PA resection, the rate of death or major disability was 0.26%. Risk factors for complications included prior surgical/radiosurgical treatment and PA invasion. No differences in complication rates between endoscopic and microscopic surgery were observed. When performed at experienced pituitary centers, safety rates for patients undergoing transsphenoidal PA resection are extremely high.

84 FACTORS INFLUENCING PROPHYLACTIC CRANIAL IRRADIATION UTILIZATION IN LIMITED STAGE SMALL CELL LUNG CANCER

Purpose: To review the results of 75 patients with arteriovenous malformations (AVMs) treated with stereotactic radiosurgery (SRS). Materials and Methods: Thirty-five men and 40 women underwent linear accelerator-based single-fraction SRS from September 1997 to August 2005. The median age was 40 years. All lesions were deemed unsuitable for surgery and/or embolization due to large size or anatomic location, or had failed prior treatment. Twenty-one patients had prior surgery and/or embolization, five patients had prior radiosurgery, and 49 patients had no prior treatment. Median lesion volume was 2.56 cm3 (range, 0.11-13.9 cm). Median prescription dose was 20 Gy (range, 12-25 Gy) to the lesion periphery, resulting in a median “12 Gy volume” of 16.6 cm (range, 1.8-84.3 cm). Patients were followed using yearly magnetic resonance imaging (MRI), with digital subtraction angiography deferred until MRI evidence of complete obliteration or until three to four years post-treatment. Median follow up using MRI and angiography was 34.0 months. Results: The two, three, four and five-year angiographic obliteration rates using Kaplan-Meier analysis were 10.0%, 43.6%, 71.2%, and 77.6%. Eighteen patients developed radionecrosis (RN) on MRI, resulting in permanent neurologic changes in 15 patients. The one, two, three and four-year actuarial rates of RN were 6.8%, 19.8%, 21.4% and 32.8%. The median time till RN was 16 months (range, 9.8-38.9 months). Three patients had AVM haemorrhage in the latent period posttreatment. Conclusion: The obliteration rate in this cohort is comparable to most published series. However, the incidence of symptomatic RN is much higher than is previously reported. This could be due to our completeness of follow up or our case selection of lesions that were larger, located in eloquent regions, or had failed prior treatment. Hypofractionated stereotactic radiotherapy, as an alternative to single-fraction SRS, is being investigated as a method of reducing symptomatic complications for larger AVMs in eloquent areas of the brain.

Salvage Gamma Knife Stereotactic Radiosurgery for Surgically Refractory Trigeminal Neuralgia

To evaluate the clinical outcome of patients with surgically refractory trigeminal neuralgia (TN) treated with rescue gamma knife radiosurgery (GKRS). Seventy-nine patients with typical TN received salvage GKRS between 1997 and 2002 at the Barrow Neurological Institute (BNI). All patients had recurrent pain following at least one prior surgical intervention. Prior surgical interventions included percutaneous destructive procedures, microvascular decompression (MVD), or GKRS. Thirty-one (39%) had undergone at least two prior procedures. The most common salvage dose was 80 Gy, although 40-50 Gy was typical in patients who had received prior radiosurgery. Pain outcome was assessed using the BNI Pain Intensity Score, and quality of life was assessed using the Brief Pain Inventory. Median follow-up after salvage GKRS was 5.3 years. Actuarial analysis demonstrated that at 5 years, 20% of patients were pain-free and 50% had pain relief. Pain recurred in patients who had an initial response to GKRS at a median of 1.1 years. Twenty-eight (41%) required a subsequent surgical procedure for recurrence. A multivariate Cox proportional hazards model suggested that the strongest predictor of GKRS failure was a history of prior MVD (p=0.029). There were no instances of serious morbidity or mortality. Ten percent of patients developed worsening facial numbness and 8% described their numbness as "very bothersome." GKRS salvage for refractory TN is well tolerated and results in long-term pain relief in approximately half the patients treated. Clinicians may reconsider using GKRS to salvage patients who have failed prior MVD.

Dynamic arc radiosurgery field shaping: a comparison with static field conformal and noncoplanar circular arcs

Purpose: Recent advances in field-shaping technology and linac multileaf collimator (MLC) integration have resulted in new approaches to performing stereotactic radiosurgery. We present a modeling study comparing the absolute dose distributions from three radiosurgery delivery techniques: a conventional approach utilizing noncoplanar circular arcs, a static field conformal approach, and a dynamic arc field-shaping approach. In the latter, the MLC leaves more in a continuous fashion, conforming to the beam’s-eye-view projection of the target at every increment along the path of an arc. Methods and Materials: For the analysis, we devised a simulated target consisting of three overlapping spheres. This was chosen because it offered a straightforward planning approach for all three techniques, primarily the multiple isocenter approach. In addition, three representative cases were selected from the prior radiosurgery experience. These range in increasing size, from 0.50 to 9.79 cm 3, and in complexity, requiring from 3 isocenters to 16 in the case of circular arcs. In each situation, the goals were twofold: (1) to cover the entire volume with as high an appropriate isodose level (90% in the case of the conformal and dynamic arc techniques, 50% in the case of circular collimators) while (2) minimizing the dose to normal brain and where applicable, any adjacent radiation-sensitive structures. Because of the latter requirement, a single isocenter circular arc approach was ruled out for the analysis. Results: In the case of large or irregularly shaped lesions, the circular arc technique requires multiple isocenters, producing a high level of dose heterogeneity within the target volume. Both the static field and dynamic arc conformal techniques, as with all single isocenter approaches, produce a highly homogeneous dose throughout the target region. For a given large dose, peripheral dose is decreased as additional beams or arc degrees are added with either of the conformal approaches. Dose–volume histogram analysis evaluating the peripheral dose shows that, in many cases, dose to surrounding structures can be reduced through the use of a conformal static or dynamic arc approach over the conventional multiple isocenter, circular arc techniques. Conclusions: Dynamic arc shaping is an efficient and effective method for accurately delivering a homogeneous target dose while simultaneously minimizing peripheral dose in radiosurgery applications.