ESTRO 2025 - Abstract Book

S376

Brachytherapy - Urology

ESTRO 2025

Purpose/Objective: Dose prescription in radiotherapy of prostate cancer varies considerably complicating the comparison of different fractionation schedules. Here, we present data on local tumor control and urinary toxicities according to the biologically equivalent dose (BED) based on the linear quadratic model. Material/Methods: We performed a planning study comparing LDR 145 Gy with HDR-brachytherapy 1*19 Gy and 2*13,5 Gy. 3 Patients (one small, medium and big size prostate) had an optimized LDR preplan in Variseed 9.0 as usual. All volume definitions for prostate,urethra,rectum were exported to Vitesse 4.0 and calculation repeated for both HDR schedules. Mean V100% was 98,3%(LDR), 97,4%(HDRbothschemes). For all, we determined typical dose parameters for prostate (D90%,D50%,average) and urethra (D30%,D10%,D1%,average). Mean EQD2 was calculated with various alpha/beta values for prostate (1,5/3/5), urethra (alpha/beta 3) and normal prostatic tissue (early reaction assumed with alpha/beta 6 and late reactions with alpha/beta 0.5). Comparisons with external beam techniques (van As (2)) were done by using the nominal prescription dose with 100% and 75 % respectively.

Results: