Salvage Radiation Therapy After Radical Prostatectomy: Analysis of Toxicity by Dose-Fractionation in the RADICALS-RT Trial

Purpose: Emerging data indicate comparable disease control and toxicity of normal postoperative fractionation and moderate hypofractionation radiation therapy (RT) in prostate cancer. In RADICALS-RT, patients were planned for treatment with either 66 Gy in 33 fractions (f) over 6.5 weeks or 52.5 Gy in 20f over 4 weeks. This non-randomized, exploratory analysis explored the toxicity of these 2 schedules in patients who had adjuvant RT.

Methods and materials: Information on RT dose was collected in all patients. The Radiation Therapy Oncology Group toxicity score was recorded every 4 months for 2 years, every 6 months until 5 years, then annually until 15 years. Patient-reported data were collected at baseline and at 1, 5, and 10 years using standard measures, including the Vaizey fecal incontinence score (bowel) and the International Continence Society Male Short-Form questionnaire (urinary incontinence). The highest event grade was recorded within the first 2 years and beyond 2 years and compared between treatment groups using the χ² test.

Results: Of 634 patients, 217 (34%) were planned for 52.5 Gy/20f and 417 (66%) for 66 Gy/33f. In the first 2 years, grade 1 to 2 cystitis was reported more frequently among the 66 Gy/33f group (52.5 Gy/20f: 20% vs 66 Gy/33f: 30%; P = .04). After 2 years, grade 1 to 2 cystitis was reported in 16% in the 66-Gy group and 9% in the 52.5-Gy group (P = .08). Other toxic effects were similar in the 2 groups, and very few patients had any grade 3 to 4 toxic effects. Patients reported slightly higher urinary and fecal incontinence scores at 1 year than at baseline, but no clinically meaningful differences were reported between the 52.5 Gy/20f and 66 Gy/33f groups. Patient-reported health was similar at baseline and at 1 year and similar between the 52.5 Gy/20f and 66 Gy/33f groups.

Conclusions: Severe toxic effects were rare after prostate bed radiation therapy with either 52.5 Gy/20f or 66 Gy/33f. Only modest differences were recorded in toxic effects or in patient-reported outcomes between these 2 schedules.