External validation of the Royal Marsden hospital stereotactic radiosurgery survival score for patients with brain metastases treated with stereotactic radiosurgery

Aims
Stereotactic radiosurgery (SRS) has been adopted as an important component of brain metastasis management. Appropriate patient selection and prognostication can prove to be challenging. We set out to analyse SRS outcomes at our tertiary referral centre in order to validate a novel prognostic tool, the Royal Marsden Hospital SRS Survival Score (RMH-SSS), using this independent data set.

Materials and methods
Patients treated with brain SRS at a regional referral centre between 2017 and 2023 were identified. Records were reviewed for details regarding demographics, primary tumour type and systemic therapy, and SRS treatment planning. The RMH-SSS was calculated, based on age, performance status, number and volume of brain metastases, the presence of extracranial disease, primary tumour histology, and molecular subtype. Kaplan-Meier time-to event analyses were undertaken according to prospectively defined clinically relevant strata.

Results
Outcomes for 242 patients with 421 metastases were analysed. All treatments were delivered by frameless LINAC-based SRS. Ten patients had radiological evidence of radionecrosis identified on magnetic resonance imaging (MRI). Median overall survival (mOS) was 15.4 months. A higher RMH-SSS was associated with improved mOS (score: 6-11 vs 0-2, hazard ratio = 0.22, 95% confidence interval [CI] = 0.14-0.36, P=<0.001).

Conclusion
RMH-SSS had prognostic value in assessment of overall survival in this external, validatory cohort comprising contemporary SRS treatment and therefore may inform patient selection for brain SRS in the clinic.