When using moderate hypofractionation for prostate cancer, is proton therapy (PBT) associated with less late toxicity than photon therapy (IMRT)? This analysis of prospectively-collected data from 1850 patients treated at seven centers compares rates of late grade 3+ GU and grade 2+ GI toxicity after either PBT or IMRT. Included patients had low to intermediate risk disease and received 2.5-3 Gy per fraction over 4-6 weeks. Two-thirds of patients were treated with IMRT and one-third with PBT. IMRT had higher acute GU toxicity while there was no difference in the rate of acute GI toxicity (4.4% IMRT, 3.8% PBT). There was no difference in the rates of late grade 2+ GU toxicity (20% IMRT, 15% PBT). Before adjusting for patient and treatment factors, late GI toxicity was actually higher with PBT (11.1% vs 4.8%). While that difference was not significant after adjusting for patient/treatment factors, the numerical difference was still apparent. Only use of anticoagulation was associated with the risk of GI toxicity. TBL: Among >1800 patients treated with moderately hypofractionated prostate radiation, proton therapy was not associated with reduced late GU or GI toxicity. | Vapiwala, Int J Radiat Oncol Biol Phys 2021


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