Cozzarini C, et al. – The unknown dose–effect relationship for late patient–reported urinary incontinence (LPRUI) was examined. For prostate cancer (PCa), LPRUI after radiotherapy (RT) dramatically depended on 2 Gy equivalent dose (EQD2) and few clinical factors. A consistency was observed between results and a larger than expected impact of moderate hypo–fractionation on the risk of LPRUI. As expected, a link was noted between baseline symptoms, as captured by ICIQ–SF, and an increased risk of LPRUI.

Methods

• The multi-centric study DUE01 incorporated patients.
• Researchers gathered clinical and dosimetry data including the prescribed 2 Gy equivalent dose (EQD2).
• Via the ICIQ-SF questionnaire filled in by the patients at RT start/end and therefore every 6 months, LPRUI was evaluated.
• Conventional (74–80 Gy, 1.8–2 Gy/fr) or moderately hypo-fractionated RT (65–75.2 Gy, 2.2–2.7 Gy/fr) in 5 fractions/week with intensity-modulated radiotherapy had been given to patients.
• They considered six different end-points of 3-year LPRUI, including or not patient’s perception (respectively, subjective and objective end-points).
• For each end-point, multivariable logistic models were developed.

Results

• They examined data of 298 patients.
• 5.1% was the incidence of the most severe end-point (ICIQ-SF>12).
• In addition, EQD2 calculated with alpha–beta=0.8 Gy showed the best performance in fitting data: the risk of LPRUI markedly increased for EQD2>80 Gy.
• The clinical factors more significantly predictive of LPRUI were previous abdominal/pelvic surgery and previous TURP.
• Confirmed by bootstrap-based internal validation, models showed excellent performances in terms of goodness-of-fit and calibration.
• Baseline symptoms were a major predictor for 5 out of six end-points when included in the analyses.