Room: Stars at Night Ballroom 4
Purpose: While whole-brain radiation therapy (WBRT) has been the standard for patients with multiple brain metastases (BM), stereotactic radiosurgery (SRS) can reduce neurocognitive toxicities. However, relapse can result in multiple courses of salvage SRS. This study evaluates whether multiple courses of Gamma Knife (MCGK) SRS result in greater doses to organs at risk (OAR) compared to single course GK (SCGK) for ten or more BM.
Methods: Twenty-six patients with at least ten BM treated with GK-SRS at our institution with the Leksell Gamma Knife between 2008 and 2018 were identified. Patients were separated into SCGK or MCGK that comprised ten or more BM. The dose-volume histograms (DVH) for OAR (brain, brainstem, optic chiasm, optic nerves, lenses, cochleae, hippocampi) were collected using Leksell Gamma Plan. The distribution of target and OAR doses from SCGK were compared to MCGK.
Results: For SCGK, the median number of BM was 13 (10-50) with a median total volume of 5.42 cc (0.37-30.17 cc). The median number of SRS courses for MCGK was 3 (2-5). MCGK had a median number of 14 (10-26) BM treated over a median of 2 years (1-6 yrs). The median total MCGK tumor volume was 8.68 cc (0.69-19.55 cc). No OAR dose comparisons (mean or maximum) reached significance (p<0.05) except a higher whole brain dose (p=0.004) for MCGK (median 38.6 vs. 34.2 Gy). Total tumor volume did not reach a significant difference, but median prescription dose for MCGK was significantly higher (p=0.0031).
Conclusion: This study demonstrates that MCGK does not dosimetrically differ from SCGK for ten or more BM except for whole brain max dose. This, in conjunction with the overall low doses delivered to critical structures in both treatment options, demonstrates that GK SRS for multi-lesion and recurrent BM cases is a viable alternative to whole brain therapy.