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MO_12_2787 - Local failure and radionecrosis following single fraction stereotactic radiosurgery for surgical cavities from brain metastases

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Local failure and radionecrosis following single fraction stereotactic radiosurgery for surgical cavities from brain metastases
F. Y. Moraes1,2, G. Shen3, J. Winter1, A. Dasgupta1,2, E. Atenafu4, C. Coolens1, B. A. Millar1,2, N. J. Laperriere1,2, M. Bernstein5, P. Kongkham5, G. Zadeh5, D. S. C. Tsang1,2, T. D. Conrad2,6, A. Berlin1,2, and D. B. Shultz1,2; 1Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada, 2Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada, 3University of Toronto, Toronto, ON, Canada, 4Department of Biostatistics, University Health Network, University of Toronto, Toronto, ON, Canada, 5Department of Neurosurgery, Toronto Western Hospital - University of Toronto, Toronto, ON, Canada, 6Radiation Medicine Program, University Health Network and Princess Margaret Cancer Centre, Toronto, ON, Canada

Purpose/Objective(s): To examine outcomes following Gamma Knife radiosurgery (SRS) targeting surgical cavities from resected brain metastases (BM) in a large multidisciplinary program.

Materials/Methods: We queried a prospectively maintained registry of 1672 patients treated with SRS between 2006 and 2017 to identify patients treated with SRS to a BM surgical cavity with at least one follow-up visit. The SRS dose (single fraction) was prescribed according to our institutional guidelines based on volume and location. Targets <4.2 cc were treated to 20Gy, 4.2 cc - <8 cc to 18 Gy, ≥8.0cc -14.4cc to 17 Gy, ≥14.4cc - <20cc to 15 Gy, ≥20cc - 30 cc to 14 Gy and ≥30cc - <5 cm to 12 Gy. Surgical cavities in eloquent areas of the brain were usually treated with a marginal prescription dose of 15 Gy. Patient, tumor, and treatment factors were assessed for their impact on patterns of failure and radio necrosis (RN). Cumulative incidences of local failure (LF) as well as RN were calculated using Fine and Grey’s analysis considering death as competing event.

Results: Eighty-four patients (91 surgical beds – median volume of 12.2cc [1cc to 47.52]) were included. Median overall survival was 27.2 months (95%CI 14.3-40.4 months) from the date of SRS. The most common primary histologies were lung (28.5%), melanoma (14%), and breast (12%). During a median follow-up of 12.6 months (range 0.76-44 months), 28 (20.9%) patients developed new BM (e.g. distant intracranial failure); 12 of these (14% of the entire cohort) received WBRT (due to leptomeningeal or multiple new BMs) and 16 (19% of the entire cohort) were treated with salvage SRS treatment only. The cumulative incidence of 1- and 2-year LF was 11.4% (95% CI 2.6-20.3%) and 31% (95%CI 15.5-46.5), respectively. The cumulative incidence of 1- and 2-year RN was 1.4% (95%CI 0-4.5%) and 7.8% (95%CI 0-16.8), respectively. On univariate analysis, surgical cavity volume (≤14.4cc vs >14.4cc) was not significantly associated with a higher rate of LF (HR=2.311 95% CI 0.809-6.60 p=0.1178) or RN (HR=1.561 95% CI 0.341-7.152 p=0.5662). Similarly, SRS prescription dose ≤15 Gy compared to 16 Gy or greater was not significantly associated with LF (HR 1.23 95% CI 0.518-2.928, p=0.6369) or RN (HR=0.483 95%CI 0.098-2.377, p=0.3708).

Conclusion: Single fraction SRS for BM surgical cavities resulted in acceptable 1-year LF and RN incidence rates, however after 2 years outcomes were not as favourable. Alternative methods of cavity treatment, such as hypofractionation and neoadjvuant SRS, may result in improved outcomes.

Author Disclosure: F. Moraes: None. G. Shen: None. A. Dasgupta: None. E. Atenafu: None. C. Coolens: Patent/License Fees/Copyright; Modus Medical. N.J. Laperriere: None. M. Bernstein: None. G. Zadeh: None.

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