ESTRO 2024 - Abstract Book

S2478

Clinical - Urology

ESTRO 2024

1974

Mini-Oral

Acute Toxicity in a Randomized Trial of MRI-guided Salvage RT for Prostate Cancer in 4 vs. 2 Weeks

Himanshu Nagar 1 , Xi Zhou 2 , Marshall Diven 3 , Christopher Barbieri 4 , Silvia Formenti 1 , Jim Hu 4 , Ana Molina 5 , David Nanus 5 , Jones Nauseef 5 , Douglas Scherr 4 , Cora Sternberg 1 , Scott Tagawa 5 , Ariel Marciscano 1 1 Weill Cornell Medicine, Radiation Oncology, New York, USA. 2 Weill Cornell Medicine, Population Health Sciences, New York, USA. 3 NewYork-Presbyterian Hospital, Radiation Oncology, New York, USA. 4 Weill Cornell Medicine, Urology, New York, USA. 5 Weill Cornell Medicine, Medical Oncology, New York, USA

Purpose/Objective:

Given promising results from NRG-GU003 comparing conventional and moderate hypofractionation in the post operative setting, there is growing interest in exploring ultra-hypofractionated post-operative regimens. It remains unclear whether this can be done safely and whether MRgRT may help mitigate potential toxicity. SHORTER (NCT04422132) is a phase II randomized trial prospectively evaluating whether salvage MRgRT delivered in 5 fractions versus 20 fractions is non-inferior with respect to EPIC gastrointestinal (GI) and genitourinary (GU) toxicities. This is an acute toxicity analysis at median of 6 months.

Material/Methods:

A total of 136 patients were randomized in a 1:1 ratio to salvage MRgRT in 5 fractions or 20 fractions using permuted block randomization. Patients were stratified according to baseline Expanded Prostate Cancer Index Composite (EPIC) bowel and urinary domain scores as well as nodal treatment and androgen deprivation therapy (ADT). Patients undergoing 5 fractions received a total of 32.5 Gy over 2 weeks and patients undergoing 20 fractions received a total of 55 Gy over 4 weeks, with or without nodal coverage (25.5 Gy over 2 weeks and 42 Gy over 4 weeks) and ADT as per the investigator's discretion. The co-primary endpoints are change scores in the bowel and the urinary domains of the EPIC. The secondary endpoints include safety endpoints, including change in GI and GU symptoms at 3, 6, 12 and 60 months from completion of treatment, and efficacy endpoints, including time to progression, prostate cancer specific survival and overall survival.

Results:

Between September 2020 and September 2023, 136 patients were randomized: 68 to 20 fractions (HYPO) and 68 to 5 fractions (SBRT). There was no evidence of difference in both the baseline GU and GI scores between patients in the two arms. The proportion of patients received ADT were also comparable between the two arms. The estimated change in EPIC GU score at 6-month from baseline in SBRT patients and the corresponding 95% CI are -5.23 [-8.35, - 2.12], i.e. there was a statistically significant decrease in EPIC GU score. The estimated change in EPIC GU score at 6 month from baseline in HYPO patients and the corresponding 95% CI are -1.94 [-6.31, 2.43]. The estimated difference in change in EPIC GU scores between the treatment SBRT and HYPO and the corresponding 95% CI are - 3.3 [-8.53, 1.93], indicating that we do not have sufficient evidence of difference in effects on EPIC GU functions between the two treatments. The estimated change in EPIC GI score at 6-month from baseline in SBRT patients and