Evidence of dose-response following hypofractionated stereotactic radiotherapy to the cavity after surgery for brain metastases.

Abstract

A retrospective review of consecutive patients between January 2012 and December 2018 receiving hypofractionated stereotactic radiotherapy (HSRT) to the cavity after resection for brain metastases was performed. Treatment was delivered using an appropriately commissioned linear accelerator. The primary outcome was time to radiological or histological confirmation of local recurrence following completion of HSRT. Dose-fractionation regimens were converted to biologically 2Gy-equivalent doses assuming α/β = 10 (EQD2[10]). Multivariate Cox proportional hazards modelling was performed to determine hazard ratios (HR) with respective 95% confidence intervals (CI). The Log-rank test was used to determine p values taking statistical significance p < 0.05. There were 134 patients and 144 cavities identified. The most common primary histologies were melanoma (n = 49) and lung (n = 32). 116 patients (87%) underwent a gross total resection. Median planning target volume (PTV) was 28 cm3 (range 2.4-149.2). Median EQD2[10] was 38.4Gy (range 22.3-59.7) and 24Gy in 3 fractions was the most common regimen. 12 (9%) patients demonstrated local recurrence at median interval 215days (range 4-594). 7 (5%) patients experienced grade 3 or higher toxicities. In multivariate analysis, EQD2[10] was associated with local failure such that increased equivalent doses improved local control [HR = 0.79 and 95% CI 0.65-0.96, p = 0.0192]. There were no significant associations for primary histology, patient age, volume of residual disease, PTV volume or location. This large series demonstrates that HSFRT to the surgical resection cavity for brain metastases has improved local control with increasing dose. Rates of grade 3 or higher toxicity were low overall.