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.