Feasibility of Urethra-Sparing Ultra-Hypofractionated Three-Dose-Level Radiotherapy for Prostate Cancer with a Dominant Intraprostatic Lesion Abutting the High-Dose Avoidance Zone

This planning study evaluated ultra-hypofractionated three-dose-level radiotherapy for prostate cancer with a dominant intraprostatic lesion (DIL) abutting the urethral high-dose avoidance zone (HDAZ). Ten patients (30 volumetric modulated arc therapy [VMAT] plans) were re-planned with 25 Gy to the pelvis, 35 Gy to the prostate, and 50 Gy to the DIL in five fractions. All plans achieved coverage while keeping urethral doses below the 90 GyEQD2 threshold and meeting organ-at-risk constraints, irrespective of DIL size or HDAZ contact. The findings demonstrate the feasibility of urethra-sparing with effective DIL dose escalation, even in peri-HDAZ locations.