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Objective: We sought to determine the risk of leptomeningeal disease (LMD) in patients treated with stereotactic radiosurgery (SRS) targeting the postoperative cavity following surgical resection of a brain metastasis, deferring whole brain irradiation (WBRT) in all patients. Methods: We retrospectively reviewed 175 brain metastasis resection cavities in 165 patients with evaluable follow-up imaging treated with post-operative SRS from 1998 to 2011. No patient had WBRT. LMD was defined through radiologic and/or pathologic findings. The local cavity, distant parenchymal brain, and leptomeningeal brain failure rates were calculated using the competing risk analyses, with death as a competing risk. Control rates were censored at the time of last follow-up or at the time of salvage WBRT. Factors associated with LMD were determined through univariate analysis. The overall survival rate was calculated using Kaplan-Meier estimates. Results: Median follow-up duration was 12 months (range, 1 - 156 months). Median overall survival was 18 months. The cumulative incidence rates of local cavity failure at 1- and 2- years were 10% and 14%, respectively. Twenty-one patients (13% crude rate) developed LMD at a median of 5 months (range, 2-33 months) following SRS. The 1- and 2- year cumulative incidence rates of LMD were 11% and 13%, respectively. Posterior fossa (p=0.5) or pial (p=0.2) location was not associated with LMD. The factors predictive for LMD on univariate analysis were new parenchymal metastases (p=0.009) and breast cancer histology (p=0.004). Both continued to be significant on multivariate analysis (p=0.03 and 0.007, respectively). The 1 year rate of LMD was 24% for breast (n=26 patients) vs. 9% for non-breast (n=139) histology. The receptor status of breast cancer patients did not correlate with risk of LMD. All LMD patients were subsequently treated with WBRT. Median survival following the diagnosis of LMD was 7 months (range, 1 - 37 months). Conclusions: Patients treated with SRS targeting the post-operative cavity following resection of breast cancer metastases have a higher risk of LMD in this series. Whether the inclusion of WBRT would decrease the rate of LMD or if the biology of breast cancer brain metastases places patients at higher risk irrespective of the treatment choice is unknown. We encourage all future reports on SRS cavity boost to include the risk of LMD. Disclosure: No significant relationships. [ABSTRACT FROM AUTHOR]

Stereotactic radiosurgery (SRS) is a highly precise form of radiation therapy initially developed to treat small intracranial lesions. The principles of cranial SRS is high precision radiation where delivery is accurate to within one to two millimeters applied with dedicated devices in one fraction. This treatment is only possible due to the development of highly advanced radiation technologies that permit maximum dose delivery within the target while minimizing dose to the surrounding healthy tissue. The goal is to deliver doses that will destroy the tumor and achieve permanent local control. Intracranial SRS can be done in an excellent way with dedicated machines. Gamma Knife and Cyberknife are two of these dedicated machines for this approach. In this study, SRS planning was performed to 11 intracranial metastases of 9 patients with the two dedicated treatment planning system. The dose volume histograms and dosimetric parameters were compared. Those parameters included heterogenity index (HI), conformality index (CI), gradient index (GI), volume of the normal brain receiving 8Gy (V8), 10 Gy (V10) and 12 Gy (V12) . The mean RTOG CI of the CK and GK treatment plans were 1.14±0,07 and 1.16±0.17 respectively where the mean Paddick CI was 0,82 ± 0,04 and 0,85 ± 0,10 (0.64-0.95) (NS). The mean GI of the CK and GK treatment plans were 3,26 ± 0,47 and 3.05±0.51 respectively (NS). GK plans were more heterogeneous than CK plans with a HI 1.98 ± 0.19 vs 1.09 ± 0,05 (p=0.003). V8, V10 and V12 values of the normal brain was not found to be different in the two treatment planning systems. GK and CK treatment planning systems are two excellent tools for stereotactic radiosurgery of solitary intracranial lesions in terms of universal dosimetric parameters. Disclosure: No significant relationships. [ABSTRACT FROM AUTHOR]

Sare KefelioÄ lu, I. Vergalasova, A. Gupta, A. Balmuk, G. Güngör, N. Ohri, J. Weiner, E. Karaarslan, E. à zyar, B. Atalar, Poster: Clinical track: CNS PO-0867: Risk of Symptomatic Radiation Necrosis Following Stereotactic Radiosurgery for Brain Metastases M. Sayan, B. Å ahin, T. Zoto Mustafayev, E.Å . [Extracted from the article]