BRAINSTEM METASTASES TREATED WITH STEREOTACTIC RADIOSURGERY AT BARTS HEALTH NHS TRUST: FEASIBILITY, TOLERABILITY AND EffiCACY

Abstract AIMS To report on the experience of patients treated at Barts Health with five-fraction stereotactic radiotherapy (SRT) for brainstem metastases. METHODS Patients included had metastatic tumours within or directly abutting the brainstem, treated with five-fraction SRT between 2020-2025. Patient and tumour characteristics, SRT planned dosimetric parameters, and toxicity were analysed. Local control, overall survival and short and long-term toxicities are presented. RESULTS 14brainstem metastases from 13 patients; 7 with lung adenocarcinoma, 5 with breast carcinoma, 1 with melanoma, were included. Median clinical follow-up was 13 months (IQR 3.5- 23 months), median radiolog- ical follow-up was 6.2 months (IQR 1-19.5 months). Mean volume of brainstem lesions was 0.68cc and mean volume of simultaneously treated intracranial lesions was 4.89cc. The median circumferential dose (D99%) to brainstem lesions was 25Gy in 5 fractions (BED = 37.5Gy10) and median maximum dose within the GTV was 34.4Gy (IQR 33.6-39.6). The maximum near dose maximum to the brainstem PRV was restricted to 31Gy in 5 fractions (per local protocol). 30.8% (4/13) of patients had prior SRT to other intracranial metastases, no patient received prior whole-brain radiotherapy. 61.5% (8/13) of patients received previous systemic anti-cancer treatment. Two weeks post SRT, 53.8% (7/13) reported no new toxicities, 30.8% (4/13) reported <G1 fatigue, 7.7% (1/13) G1 dizziness and 7.7% (1/13) G1 headache. Long-term, there were no grade 3-5 neurological toxicities and no toxi- cities specifically attributed to SRT. 53.8% (7/13) of patients were alive at last follow-up. Long-term progression data was available for 12 of 13 patients. Local control was achieved in 75% (9/12) of treated brainstem lesions. CONCLUSION Our study provides evidence that five-fraction SRT for patients with brainstem metastases and limited intracra- nial disease is safe, effective and feasible. Circumferential doses of 25Gy are achieved with five-fraction SRT and it results in excellent local control, minimal short-term side-effects and no serious long-term sequalae.