3303 - Daily Adaptive RadioTherapy in Postoperative HypofrActionated Salvage radiothERapy for Prostate Cancer Patients (DART-PHASER): Early Clinical and Dosimetric Results
Presenter(s)
L. Nicosia1, R. F. Borgese2, N. Bianchi2, C. Orsatti2, A. G. Allegra2, M. Corsi3, C. De-Colle2, A. De Simone1, N. Giaj-Levra2, D. Gurrera2, S. Naccarato2, E. Pastorello2, F. Ricchetti2, M. Rigo2, A. Romei2, G. Sicignano2, R. Ruggieri1, and F. Alongi2; 1Department of Advanced Radiation Oncology, IRCCS Sacro Cuore Don Calabria Hospital, Cancer Care Center, Negrar di Valpolicella, Italy, 2Department of Advanced Radiation Oncology, IRCSS "Sacro Cuore Don Calabria Hospital" Cancer Care Center, Negrar di Valpolicella (VR), Italy, 3Medical Physics Unit, IRCSS "Sacro Cuore Don Calabria Hospital" Cancer Care Center, Negrar di Valpolicella (VR), Italy
Purpose/Objective(s):
Salvage radiotherapy (sRT) is commonly used for locoregional prostate cancer (PC) relapse. Modern technology like adaptive RT can help in improving safety and accuracy of those treatments. Ethos system uses daily imaging and artificial intelligence to adjust treatment plans based on daily anatomy. This might set a new standard in the setting of sRT, balancing efficacy with reduced toxicity. We report the preliminary toxicity results of moderately hypofractionated adaptive sRT.Materials/Methods: This is a prospective observational study (NCT05884632) evaluating the safety and efficacy of 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 EthosTM, an AI-powered system that adjusts treatment plans based on daily anatomical changes. EthosTM 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 selects the preferred one for treatment. Primary endpoint was acute gastrointestinal (GI) toxicity reduction compared to historical series, assessed via CTCAE v5.0. Secondary end-points include genitourinary (GU) toxicity, quality of life (EORTC QLQ-C30, EPIC), and biochemical failure.
Results: The results of the first 840 treatment fractions in 42 patients are reported. The median age was 64 years (range 33-78). Sixteen (37.2%) had biochemical relapse only, while 27 (62.8%) had macroscopic relapse. The median rectum V52.8Gy among 840 treatment fractions was 16.9% and 12.8% in the schedule and adapted plan, respectively (p=<0.0001), and the median rectum Dmean per fraction was 1.54Gy and 1.42 Gy for the scheduled and adapted plan respectively (p=<0.0001). The median prostate bed PTV95%, was 92.1% and 98.5%, in schedule and adapted plan, respectively (p=<0.0001). We found a significant improvement for pelvis PTV95% (<0.0001), pelvis PTV107% (<0.0001), and bowel Dmax (<0.0001) in the adapted plan, compared to the scheduled plan. There was no difference in the median value for prostate bed PTV107%, bladder Dmean, and bladder V40.8Gy. See details in table 3.
Grade 2 GI toxicity (worst grade) was: G2 4.8%. Grade 2 GU toxicity (worst grade) was 9.5% of cases. In the univariate analysis, the only factor associated with diarrhea onset was the inclusion of the pelvis (p=0.002). There was no difference between treatment dose and toxicity at any time frame (2 weeks, end of treatment, 3 months after RT).Conclusion: Preliminary data seems to show minimal acute toxicity. CT-based adaptive moderate hypofractionated radiotherapy might be beneficial in the PC postoperative setting. A longer follow up is needed to confirm these data and evaluate late toxicity.