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PURPOSE/OBJECTIVE(S) Most Gamma Knife stereotactic radiosurgery (GKRS) procedures have been performed using water-based dose calculation algorithms with magnetic resonance imaging (MRI) only. We present a dose calculation method that can take into account the inhomogeneity effect in routine GKRS treatment planning without CT imaging for every patient. MATERIALS/METHODS Twenty-five patients who underwent GKRS at our institution with T1- and T2-weighted whole head MRI as well as brain CT images were selected for this study. Two set of synthetic computed tomographies (sCT) were generated from T1 and T2 MRI using cycle consistent generative adversial networks architecture (cGAN). Images from 20 patients were used to train the algorithm. The other 5 sets of data were used for testing and validation. The sCT images generated were evaluated in terms of the preservation of anatomical structures, the Hounsfield unit accuracy and the overall image quality. All sCT images from the 5 test patients were imported into GammaPlan version 11.1 for dosimetric analyses. We performed dose calculations for each test patient using the water-based TMR algorithm and the convolution algorithm with electron densities from the original CT, the T1-based sCT and the T2-based sCT. RESULTS The main features of the original CT images (skull shape, bone & air inhomogeneity etc.) for the 5 test patients were successfully reproduced in the sCT images. sCT images from the T1-weighted MRI are in general closer to the original CT images compared to the T2-weighted MR images. For the same dose prescription and same shot arrangement, the maximum difference between the treatment shot times from the CT-based convolution calculation and the TMR calculation is 10.2%. The maximum differences between the treatment shot times from the CT-based convolution calculation and the convolution calculations from the sCTs from the T1 and T2 MR images are 2.3% and 3.8%, respectively. CONCLUSION sCT images from brain MRI can be used for the inhomogeneity correction in GKRS dose calculation. T1-weighted MRI may work better than T2-weighted MRI for this purpose. AUTHOR DISCLOSURE F. Li: None. Y. Xu: None. O.D. Lemus: None. T.J. Wang: Research Grant; AbbVie, Merck, RTOG Foundation, Genentech. Honoraria; Elekta, Wolters Kluwer, Cancer Panels, Rutgers, University of Iowa. Consultant; Doximity, Elekta. Advisory Board; Novocure, AstraZeneca. Travel Expenses; AbbVie, Elekta, Novocure. Stock Options; Doximity. M.B. Sisti: None. C. Wuu: None.

Objective Subependymomas are infrequent, low-grade gliomas associated with the ventricular system and the spinal cord. Little is known about the origin and natural history of these slow-growing lesions. Methods We identified all patients with pathologically proven subependymomas presenting to our institution between 1998 and 2016. We retrospectively reviewed clinical, radiographic, histologic, and surgical outcomes data in all patients who underwent surgical resection. Immunohistochemical analyses for cell lineage markers were performed. Results A total of 31 patients with pathologically proven subependymomas were identified. Of these, 7 asymptomatic lesions were discovered at autopsy and 24 symptomatic cases were treated surgically. There were 15 (48%) lateral ventricle tumors, 11 (35%) fourth ventricular tumors, and 5 (17%) spinal tumors. Symptomatic intracranial lesions most commonly presented with headaches and balance and gait abnormalities. Subependymomas had no distinguishing radiographic features that provided definitive preoperative diagnosis. At last follow-up, no patient treated surgically experienced recurrence. Immunohistochemical analyses demonstrated a diffusely GFAP-positive glial neoplasm with mixed populations of cells that were variably positive for Olig2, NHERF1, Sox2, and CD44. The Ki67 proliferation index was generally low ( Conclusions Subependymomas demonstrate mixed populations of cells expressing glial lineage markers as well as putative stem cell markers, suggesting these tumors may arise from multipotent glial progenitors that reside in the subventricular zone. Definitive diagnosis requires surgical sampling. Although the clinical course of subependymomas appears benign, the inability to radiographically diagnose these lesions, and the possibility of an alternative malignant lesion support a low threshold for early and safe maximal resection.

Background Frailty is an emerging means of assessing overall health status and guiding management for geriatric patients. Frailty is associated with outcomes for many surgical indications in this age group. While half of all glioblastoma patients are 65 years old or older, frailty has not been examined in relation to surgery for glioblastoma. Methods We performed a retrospective study of patients age 65 years and older with pathologically confirmed glioblastoma at Columbia Presbyterian Hospital from 2000 to 2012; 319 patients were identified, 243 of whom underwent craniotomy for lobar lesions. Frailty was quantified using the Canadian Study of Health and Aging Modified Frailty Index. Postoperative complications were classified according the Glioma Outcomes Project system. Systemic, regional, neurologic, and overall complications were examined in relation to age, Karnofsky performance status, frailty, comorbid disease burden, cardiovascular risk, and tumor sidedness. Results Frailer patients were less likely to undergo surgical resection (P = 0.0002; odds ratio [OR], 0.15; 95% confidence interval [CI], 0.05–0.40) as opposed to biopsy, had longer hospital stays (log-rank test for trend, P = 0.0061), an increased overall risk of complications (P = 0.0123; OR, 1.40; 95% CI, 1.08–1.83), and decreased overall survival (Log rank test for trend, P = 0.0028). Conclusions Frailer patients with glioblastoma receive less aggressive intervention, have longer hospital stays, and experience more complications. Frailty may be an underused metric for the preoperative risk assessment of geriatric glioblastoma patients.

Background Glioblastoma (GBM) occurs more commonly in elderly patients. However, these patients are often excluded from clinical trials. The absence of solid evidence has resulted in a nihilistic view of GBM in the elderly and a traditionally conservative treatment approach. In particular, the safety of surgical resection for both primary and recurrent GBM is poorly understood in elderly patients. Methods In a retrospective cohort of patients aged ≥65 years, we examined selection for biopsy, surgical resection, and reoperation for recurrent disease. We also analyzed complication rates after initial resection and reoperation for recurrent disease. We identified 319 elderly patients with pathologically proven GBM who underwent a total of 274 craniotomies at our institution between 2000 and 2012. Events were reported according to the methods used in the Glioma Outcomes Project. Results The overall rate of complications after resection was 21.9%, with a rate of neurological complications of 7.7%. The rates of neurological, regional, and systemic complications were not significantly different after initial craniotomy and reoperation for GBM in elderly patients. Reoperations were not associated with an increased risk of complications. Low cardiovascular risk, improved functional status, and hemispheric GBM were associated with selection for more aggressive surgical treatment. Younger age and improved functional status were associated with a reduced likelihood of complications. Conclusions We conclude that in select patients, age alone should not preclude the decision to pursue aggressive surgical management.

Chemotherapy for brain tumours has been limited because of difficulty in achieving adequate exposure to the tumour without systemic toxicity. We have developed a method for local sustained release of chemotherapeutic agents by their incorporation into biodegradable polymers. Implantation of the drug-impregnated polymer at the tumour site allows prolonged local exposure with minimal systemic exposure. We conducted a randomised, placebo-controlled, prospective study to evaluate the effectiveness of biodegradable polymers impregnated with carmustine to treat recurrent malignant gliomas. In 27 medical centres, 222 patients with recurrent malignant brain tumours requiring re-operation were randomly assigned to receive surgically implanted biodegradable polymer discs with or without 3.85% carmustine. Randomisation balanced the treatment groups for all of the prognostic factors examined. Median survival of the 110 patients who received carmustine polymers was 31 weeks compared with 23 weeks for the 112 patients who received only placebo polymers (hazard ratio = 0.67, p = 0.006, after accounting for the effects of prognostic factors). Among patients with glioblastoma, 6-month survival in those treated with carmustine-polymer discs was 50% greater than in those treated with placebo (mortality = 32 of 72 [44%] vs 47 of 73 [64%], p = 0.02). There were no clinically important adverse reactions related to the carmustine polymer, either in the brain or systemically. Interstitial chemotherapy delivered with polymers directly to brain tumours at the time of surgery seems to be a safe and effective treatment for recurrent malignant gliomas.

Arteriovenous malformations (AVMs) of the brain stem are, fortunately, rare clinical entities. Prompt diagnosis and anatomic evaluation of patients with brain stem hemorrhages resulting from AVMs have been greatly facilitated by high-resolution CT scanning and particularly MR image scanning. The goal of any treatment is complete occlusion of the malformation with minimal risk to the patient, primarily to prevent rebleeding and further neurologic injury from the AVM.

Orbital and Periorbital Complications of Proton Beam Radiation Therapy for Intraocular Tumor Y.J. Choi, S. Kim, H.K. Choung, and Y.S. Yu; Department of Ophthalmology, Kangdong Sacred Heart Hospital, Hallym University Medical Center, Seoul, South Korea, Department of Radiation Oncology, Seoul Metropolitan Government Seoul National University Boramae Medical Center, Seoul, South Korea, Department of Ophthalmology, Seoul Metropolitan Government Seoul National University Boramae Medical Center, Seoul, South Korea, Department of Ophthalmology, College of Medicine, Seoul National University, Seoul, Korea, Seoul, South Korea, Department of Ophthalmology, Seoul National University Hospital, Seoul, Korea, Seoul, South Korea