Effect of non-consecutive treatment during hypofractionated stereotactic radiosurgery (HF-SRS) for brain metastases

Background Hypofractionated stereotactic radiosurgery (HF-SRS) has become a mainstay of treatment for patients with brain metastases (BM). However, HF-SRS schedules involving 3–5 fractions may not align with conventional 5-day clinical workflows due to interruptions over weekends or holidays. We seek to compare the rate of local failure (LF) and radiation necrosis (RN) in patients using HF-SRS for BM, treated on consecutive or non-consecutive days. Methods A retrospective review from 2018 to 2023 identified adult patients who underwent HF-SRS for lung and breast cancer BM with more than 3 months of radiological imaging follow-up at a single center. Demographic data, tumor and treatment characteristics including biologically equivalent dose with α/β of 10 (BED10), and imaging-based progression outcomes were collected; LF and RN were assessed via log-rank test. Results Of the 197 included lesions from 76 patients, 84 (42.6%) experienced interruptions (median: 3.0 days) in HF-SRS treatment. There were 49 (64.5%) lung and 27 (35.5%) breast cancer patients. Between consecutive and non-consecutively treated groups, the median radiological follow-up was 11 versus 14.5 months (p = 0.42), mean gross tumor volume (GTV) was 1.6 versus 2.8 cc (p = 0.30), and mean BED10 was 51.3 versus 51.3 Gy (p = 0.34). There was no significant difference between the interrupted and non-interrupted subgroups for the probability of LF (p = 0.620) nor probability of RN (p = 0.717). BED10 was inversely associated with LF on univariable (p = 0.005) and multivariable analysis (p = 0.003). GTV trended towards increased risk of RN on univariable analysis (p = 0.08). Sub-group analysis did not demonstrate an effect of treatment interruption on LF or RN in surgically resected lesions (p = 0.721, p = 0.509) or lesions treated with SRS only (p = 0.436, p = 0.790). Conclusions Despite potential differences in radiobiological parameters, there was no significant difference in LF or RN in patients with BM from lung or breast carcinoma treated with consecutive versus nonconsecutive HF-SRS. Brief interruptions do not appear to need avoidance in patients undergoing HF-SRS when necessitated by workplace factors.