S1227
Clinical - Urology
ESTRO 2026
Mini-Oral 2351
No toxicity benefit with proton versus photon therapy for prostate cancer: two-year results from the ProtoChoice-P prospective matched-pair study. Tobias Hölscher 1,2 , Annapaula Redlich 1 , Lydia Koi 1 , Steffen Löck 1,2 , Mechthild Krause 1,3 , Michael Baumann 4 1 Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, TUD Dresden University of Technology, Dresden, Germany. 2 OncoRay – National Center for Radiation Research in Oncology, Faculty of Medicine, Dresden, Germany. 3 German Cancer Consortium (DKTK), Partner Site Dresden, and German Cancer Research Center (DKFZ), Heidelberg, Germany. 4 German Cancer Research Center, (DKFZ), Heidelberg, Germany Purpose/Objective: Proton beam therapy (PBT) for prostate cancer bases on the hypothesis of superior normal tissue sparing
compared to intensity-modulated photon radiotherapy (IMRT). However, high-quality
prospective data comparing patient-reported and physician-assessed toxicity outcomes are limited. The ProtoChoice-P study aimed to evaluate whether PBT reduces moderate-to-severe late toxicity compared to photon IMRT in definitive radiotherapy for prostate cancer. Material/Methods: This prospective, non-randomized matched-pair phase 2 study (NCT02766686) enrolled patients with localized prostate cancer (T1-3b N0M0) receiving definitive PBT or IMRT at a single institution. Treatment allocation was based on patient preference, clinical eligibility (patients with cardiac pacemakers or hip arthroplasty were excluded from PBT), and insurance approval for proton therapy. Conventional fractionation was used (74-80 Gy(RBE), 2.0 Gy(RBE)/fraction). Image-guided radiotherapy with daily positioning control and rectal balloon were employed. The primary endpoint was the cumulative incidence of combined moderate-to-severe ( ≥ grade 2, CTCAE v4.0) gastrointestinal (GI) and genitourinary (GU) toxicity within 24 months. Patients were matched 1:1 based on high-dose CTV volume, age, androgen deprivation, prior urological procedures, obstructive symptoms, risk factors for abdominal adhesions or rectal bleeding. Statistical analysis used McNemar's test for matched pairs. The study was powered to detect a reduction from 15% (IMRT) to 7.5% (PBT) with 80% power at α =0.05, requiring 131 matched pairs. Results: Between 2016 and 2024, 263 patients were evaluable (168 PBT, 95 IMRT). Matching yielded 92 pairs with concordance for risk factors. For the primary endpoint (any GI or GU toxicity ≥ grade 2 within 24 months), no
Conclusion: In the largest reported cohort of cT4M0 prostate cancer, a 5-year BFFS of 74% was achieved with definitive dose-escalated radiotherapy and long-term ADT. The extent of T4 disease was identified as prognostic, suggesting scope for systemic intensification with more refined risk stratification. Keywords: locally advanced prostate cancer, prostate RT
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