Long-term disease outcome and volume-based decision strategy in a large cohort of multiple brain metastases treated with a mono-isocentric linac-based Stereotactic Radiosurgery technique.

PURPOSE: Radiosurgery (SRS) is an effective treatment option for brain metastases (BMs). Long-term results of the first worldwide experience with a mono-isocentric, non-coplanar, linac-based stereotactic technique in the treatment of multiple BMs are reported.

METHODS: patients with multiple BMs, life expectancy > 3 months, and good performance status (≤ 2) were treated with simultaneous SRS with volumetric modulated arc technique. Data were retrospectively evaluated.

RESULTS: 172 patients accounting for 1079 BMs were treated at our institution from 2017 to 2020. The median number of treated metastases was 4 (range 2-22). Primary tumor histology was: lung (44.8%), breast (32%), and melanoma (9.4%). The 2-year LPFS was 71.6%, respectively. A biological effective dose (BED) ≥ 51.3 Gy10 correlated with higher local control. Uncontrolled systemic disease and melanoma histology were independent prognostic factors correlated with decreased iPFS. Patients with > 10 BMs had a trend towards shorter iPFS (p = 0.055). 31 patients received multiple SRS courses (2-7) in case of intracranial progression. The median iOS was 22.4 months. Brainstem metastases and total PTV > 7.1 cc correlated with shorter iOS. The 1- and 2-year WBRT-free survival was 83.2% and 61.1%, respectively.

CONCLUSION: Long-term results in a large patient population treated with a mono-isocentric, dedicated technique demonstrated its effectiveness and safety also in the case of multiple courses. The shortened treatment time and the possibility to safely spare healthy brain tissue allows the safe treatment of patients with a large number of metastases and to deliver multiple courses of SRS. In selected cases, the administration of WBRT can be delayed.