ESTRO 2021 Abstract Book

S1149

ESTRO 2021

Conclusion The clinical rectal volumes were generally larger than the standard volumes with differences more notable in the cranial part than in the caudal part, notably among patients reporting late rectal bleeding. Overlaps between the two volumes were high and resulting dose differences small. With too generous clinical rectal volumes in low-dose regions, effects by higher-dose regions may be underestimated. It is not unlikely that volume-based dose-constraints for rectum in the clinical plan had not been satisfied for some patients given an adjusted upper rectal border, but this needs to be investigated further.

Digital Poster: Urology-non-prostate

PO-1398 SRS for brain metastases from renal cell carcinoma; UK tertiary referral centre 5-year experience R. Bowen 1 , A. Hashmi 1 , J. Lewis 1 , A. Hassani 1 , R. Mohanraj 1 , J. Mott 1 , R. Pearson 1,2 1 The Newcastle-upon-Tyne Hospitals NHS Foundation Trust, Northern Centre for Cancer Care, Newcastle- upon-Tyne, United Kingdom; 2 Newcastle University, Institute for Translational and Clinical Research, Newcastle-upon-Tyne, United Kingdom Purpose or Objective 13-20% 1,2 of RCC patients develop brain metastases (BMs); incidence is increasing due to increased lines of therapy and improved access to imaging. This study evaluated outcomes for patients with BMs from RCC treated with SRS at a UK tertiary referral centre. Materials and Methods Patients with RCC who had BMs treated with SRS from 2015 to 2020 were identified. Data was collected on patient demographics, tumour histology, surgical history, systemic anti-cancer therapy, radiotherapy treatments and outcomes. Results 31 patients underwent SRS to BMs from RCC from June 2015 to May 2020. 96.8% (n=30) were clear cell carcinomas. 77.4% male (n=24), median age at time of SRS was 65 years (range 46-79). 74.2% (n=23) patients were PS0-1. 80.7% (n=25) of the patient group had lung metastases when BMs were diagnosed. Median time between diagnosis of metastatic disease and first SRS treatment was 18.6 months (range 1.3 months to 90.2 months). An increasing number of patients were treated each year, from 1 patient in 2015 to 14 patients in 2019. 54 areas were treated: 37 intact metastases and 17 cavities following neurosurgery. 32.3% (n=10) had cavity alone treated, 48.3% (n=15) had intact metastases treated, and 19.4% (n=6) had cavity and intact metastases treated synchronously or sequentially. Median number of lesions treated per patient was 1 (range 1-4). The commonest treatment schedule was 21 Gy in 38.9% (n=21). Post treatment surveillance MRI scans were scheduled 3-monthly. 1 patient suffered symptomatic radiation-associated necrosis during follow up. Median interval from SRS to last follow up or death was 10.5 months (range 0.2 – 68). 19.4% (n=6) died within 3-months of SRS treatment, of systemic +/or intracranial progression. Eleven patients remain alive, 3 treated in the last 12 months and follow up continues. Median survival for the cohort was 16.5 months (95% CI 5.6- 27.4). For patients who had SRS to intact metastases only median survival 5.5 months (95%CI 0.8-10.1, n=15) and those who had cavity SRS +/- intact metastasis SRS median survival 20.1 months (95% CI 10.1-30, n=16). No lesions treated with SRS showed progression on post treatment MRI (n=16) but new lesions were identified and treated if appropriate. Conclusion SRS is an effective treatment for BMs from RCC with median survival of 16.5 months increasing the ability to deliver further systemic treatment options. MRI surveillance may facilitate earlier detection of subsequent BMs aiding outcomes. Patients receiving SRS to neurosurgical cavity appear to have better survival in this cohort. Refs: 1. Xue J, Chen W, Xu W, Xu Z, Li X, Qi F, Wang Z. Patterns of distant metastases in patients with clear cell