ESTRO 2025 - Abstract Book

S377

Brachytherapy - Urology

ESTRO 2025

The EQD2 for tumor tissue based on an a/b of 1,5 is highest in both HDR regimens and SBRT @75% and much lower in LDR, normofractionation and SBRT@100% schedules. However, the EQD2 tumor D90 and D50 in HDR regimens and 5fxSBRT dramatically decreases in tumors with an a/b of 3 or 5 and are here much lower than in LDR. The EQD 2 (D30,D10,D1) for urethra is quite similar between all regimens, suggesting that different early and late toxicities cannot be solely explained by comparing the urethral doses. The early urinary toxicity might correlate best with prostate D90, which is highest for LDR. The highest EQD2 for late reacting prostate tissue is seen in ultrahypofractionation. Also the low longterm toxicity of appropriate LDR seems to be supported by very low EQD2(D90prostate) of 42,61 Gy for late reacting tissue with an a/b of 0,5. In SBRT 5*7,25 it is about 112,4 to 196,5 Gy and in HDR 194,57 to