Selected-Lesion Stereotactic Radiosurgery in Treatment of Patients with Multiple Brain Metastases: A Single Institution Retrospective Study

Abstract

Stereotactic Radiosurgery (SRS) has been increasingly used as first and subsequent-line treatments for brain metastases. While the appropriate cut-off number of lesions for SRS is still being debated nationally in patients with multiple brain metastases, some institutions use an alternate approach particularly for patients with >10-15 lesions. Selected-lesion SRS (SL-SRS) is where only a subset of lesions are chosen for initial SRS treatment leaving small and clinically inconsequential lesions for treatment using alternate or delayed treatments. This study aims to investigate the patient selection criteria, patient and tumor characteristics and analyze the outcomes in patients receiving SL-SRS for brain metastases at our institution. Clinical data from patients treated using the SL-SRS approach from 2012-2022 at our institution were retrospectively reviewed. Patients were divided into cohorts based on overall survival from time of SL-SRS treatment and indications for using SL-SRS. We compared the patient characteristics (age, histology, KPS, dsGPA), tumor characteristics (cumulative tumor volumes, tumor dose, number of brain metastases found, number of metastases treated), treatment characteristics (chemotherapy, immunotherapy, previous SRS/ radiation, previous WBRT) and the reason for decision to recommend SL-SRS across these cohort. A total of 102 patients were treated using the SL-SRS approach. Indications for using SL-SRS were immunotherapy trial (n = 40), CNS penetrating drug options available (n = 18), patient refusing WBRT (n = 6), palliative after prior WBRT/SRS (n = 28), WBRT planned to follow SRS (n = 9). 31 patients were alive at 12 months and 21 patients at 24 months. In patients surviving <12 months - the most common indications for SL-SRS were CNS palliation in the setting of progressive disease after prior WBRT or SRS. Patients in this group had median KPS< = 60 and had predominantly non-small cell carcinoma primary diagnosis. In those patients surviving >12 months - the most common indication for SL-SRS was participation in CNS-penetrant agent clinical trials without WBRT. Patients in this group were more likely to be female, had a median KPS of 90, had predominantly diagnoses of melanoma. Following the SL-SRS treatment, 14 patients required further SRS and 4 patients went on to WBRT in the >12-month survival group. No patients died of CNS progression alone. 10 patients survived 24 months without requiring further CNS radiation. In our institution, SL-SRS has predominantly been used either as palliative treatment at time of disease progression or to facilitate entry onto clinical trial with immunotherapy or potentially CNS-penetrant agents. The latter indication resulted in 47.6% patients surviving >24 month without the need for additional radiation to the CNS and therefore SL-SRS should be considered a feasible, safe and effective alternative to either WBRT or SRS treatment of all radiographically visible brain metastases.