Daily adaptive radiotherapy in postoperative hypofractionated salvage radiothERapy for prostate cancer patients (DART-PHASER): Early clinical and dosimetric results.

Abstract

BackgroundTo evaluate dose-volume histogram metrics and preliminary toxicity of prostate cancer (PC) patients affected by postoperative locoregional relapse treated with moderately hypofractionated salvage radiotherapy (sRT) using AI-assisted daily adaptive RT.MethodsThis is a prospective observational study (4181CESC, NCT05884632) on adaptive hypofractionated sRT in PC. Eligible patients (up to 80 years old, post-prostatectomy, PSMA PET-CT confirmed M0) received 20 daily fractions up to 59 Gy for macroscopic relapse and 55 Gy for biochemical-only relapse. When indicated, pelvis was included with a dose of 45 Gy. The treatment was administered using Ethos™ system which generates two plans: scheduled and adapted. The scheduled plan includes a dose recalculation on daily synthetic CT (generated from daily CBCT). The adapted plan consists on a reoptimization based on the daily anatomy. The user then select the preferred one for treatment. This is an interim analysis reporting on DVH metrics (scheduled versus adapted plan) and toxicity outcome.ResultsThe results of the first 840 treatment fractions in 42 patients are reported. Sixteen (37.2%) had biochemical relapse only, while 27 (62.8%) had macroscopic relapse. We reported a significant improvement between scheduled and adapted plan for rectum V52.8Gy (16.9% versus 12.8%); p ≤0.0001), rectum Dmean per fraction (1.54Gy/fraction versus 1.42 Gy/fraction; p ≤0.0001), prostate bed PTV95%, (92.1% versus 98.5%; p ≤0.0001), pelvis PTV95% (p = 0.002). There was no difference between treatment dose and toxicity.ConclusionPreliminary data seems to show minimal acute toxicity. A longer follow up is needed to confirm these data and evaluate late toxicity.