Feasibility of linac-based fractionated stereotactic radiotherapy and stereotactic radiosurgery for patients with up to ten brain metastases.

Background: Linac-based fractionated stereotactic radiotherapy (fSRT) and stereotactic radiosurgery (SRS) are increasingly being used to manage patients with multiple metastases. This retrospective cohort study aimed to compare the outcomes after linac-based fSRT and SRS between three patient groups classified based on the number of brain metastases (BMs): 1 BM, 2-4 BM, 5-10 BM.

Methods: The data of consecutive patients with 1-10 BMs treated with fSRT or SRS between July 2016 and June 2018 at a single institution were collected. Patients with previous whole-brain radiotherapy (WBRT), concurrent use of WBRT, or surgical resection were excluded from the analysis. A total of 176 patients were classified into three groups according to the number of BMs: 78, 67, and 31 patients in 1 BM, 2-4 BM, and 5-10 BM, respectively. The Kaplan-Meier method was used to estimate overall survival (OS) curves, and the cumulative incidence with competing risks was used to estimate local control (LC), distant intracranial failure (DIF), and radiation necrosis (RN).

Results: Median OS was 19.8 months (95% confidence interval [CI] 10.2-27.5), 7.3 months (4.9-11.1), and 5.1 months (4.0-9.0) in 1 BM, 2-4 BM, and 5-10 BM, respectively. Compared to 2-4 BM, 1 BM had significantly better OS (hazard ratio [HR] 0.59, 95% CI 0.40-0.87; p = 0.0075); however, 5-10 BM had comparable OS (HR 1.36, 95% CI 0.85-2.19; p = 0.199). There was no significant difference in LC, DIF, and RN between tumor number groups, but DIF was lower in 1 BM. RN of grade 2 or higher occurred in 21 patients (13.5%); grade 4 and 5 RN were not observed.

Conclusions: The linac-based fSRT and SRS for patients with 5-10 BMs is comparable to that for patients with 2-4 BMs in OS, LC, DIF, and RN. It seems reasonable to use linac-based fSRT and SRS in patients with 5-10 BMs.