Emerging data indicate comparable disease control and toxicity of postoperative normo-fractionation and moderate hypofractionation radiotherapy (RT) in prostate cancer. In RADICALS-RT, patients were planned for treatment with either 66Gy in 33 fractions over 6.5 weeks or 52.5Gy in 20 fractions over 4 weeks. In this non-randomized, exploratory analysis, we explore the toxicity of these two schedules in patients who had adjuvant RT.
Information on RT dose was collected in all patients. Radiation Therapy Oncology Group toxicity score was recorded every 4 months for 2 years, 6-monthly until 5 years, then annually until 15 years. Patient-reported data were collected at baseline, 1, 5, and 10 years with use of standard questionnaires including Vaizey (bowel) and International Continence Society Male Short-Form (urinary incontinence). The highest grade of event was recorded within the first 2 years, and beyond 2 years, and compared between treatment groups using the χ² test.
217/634 (34%) patients were planned for 52.5Gy/20f and 417/634 (66%) for 66Gy/33f. In the first two years, grade 1 – 2 cystitis was reported more frequently among the 66Gy/33f group (52.5Gy/20f: 20% vs 66Gy/33f: 30%, p=0.04). After two years, grade 1-2 cystitis was reported in 16% in the 66Gy group, and 9% in the 52.5Gy group (p=0.08). Other toxicities were similar in the two groups and very few patients had any grade 3 – 4 toxicity. Patients reported slightly higher urinary and faecal incontinence scores at one year than at baseline, but no clinically meaningful differences were reported between 52.5Gy/20f and 66Gy/33f groups. Patient reported health was similar at baseline and at one year, and similar between 52.5Gy/20f and 66Gy/33f groups.
Severe toxicity is rare after prostate bed radiotherapy with either 52.5Gy/20f or 66Gy/33f. Only modest differences were recorded in toxicity or in patient reported outcomes between these two schedules.

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