ESTRO 2021 Abstract Book

S872

ESTRO 2021

standard prescription dose was 27 Gy in 3 fractions of 9 Gy. If the OAR constraints were not met, the fractionation schedule was modified to 3 fractions of 8 Gy or 7 Gy or to 5 fractions of 6 Gy or 5 Gy. Survival curves were generated by Kaplan-Meier analysis with timings from the start of treatment. Associations of patient, tumor and treatment characteristics (primary tumor site, age, Karnofsky performance score (KPS), association with immunotherapy, definitive vs adjuvant SRT, PTV volume, dose fractionation, prior whole brain radiotherapy (WBRT) and overall treatment time (OTT)) with clinical outcomes and risk of RN were assessed by Cox and logistic regression respectively. Variables with univariable significance level p<0.1 were combined in multivariable analysis. Results Forty-six patients with 73 BM were identified and included in this study. Median age was 64 years and the median KPS was 80%. Median tumor volume was 4.9 cc. Patient characteristics are shown in table 1. At a median follow up time of 11.1 months, the median overall survival (OS) was 17.5 months. Local recurrence occurred in 12 lesions (16%), none of which were in the adjuvant group. At multivariable analysis, age above 75 years (p=0.0049) and KPS 80% or lower (p=0.0085) were associated with worse OS. In the 3-fraction group, OTT > 6 days (p=0.015) was associated with worse OS at multivariable analysis. Treating more than 1 BM was also associated with worse OS (p=0.04), however only in univariable analysis. Twenty-one patients developed a distant intracranial relapse at a median time of 11.6 months. RN occurred in 8 lesions (11%) but only 3 (4%) were symptomatic. Given the limited occurrence of RN, no significant association could be found in the univariable analysis.

Conclusion MF-SRT in patients with brain metastases for solid tumors yields excellent local control rates and low incidences of RN. Further analysis of the dosimetric data will be performed for ESTRO 2021.

PO-1047 Prospective evaluation of 167 brain metastases in Indian patients treated with robotic radiosurgery S. K 1 , R. Kamath 1 , A. Gupte 1 , A. Sasidharan 1 , P. K U 1 , A. R 1 , H. Nair 1 , A. E H 2 , D. Dutta 1

1 Amrita Institute of Medical Sciences, Radiation Oncology, Kochi, India; 2 Amrita Institute of Medical Sciences, Medical Physics, Kochi, India

Purpose or Objective To evaluate the outcome, probability and patterns of recurrence, retreatment incidence and toxicities in patients treated for brain metastases with linac based robotic radiosurgery in Indian patient population. Materials and Methods Between May 2017 and February 2021, 100 patients with 167 brain metastases were accrued prospectively and treated with robotic radiosurgery (CK) (M6, Multiplan, VOLO). Patients with small volume oligo brain