Urinary symptoms following external beam radiotherapy of the prostate: Dose-symptom correlates with multiple-event and event-count models

© 2015 Elsevier Ireland Ltd. Background and purpose This study aimed to compare urinary dose-symptom correlates after external beam radiotherapy of the prostate using commonly utilised peak-symptom models to multiple-event and event-count models which account for repeated events. Materials and methods Urinary symptoms (dysuria, haematuria, incontinence and frequency) from 754 participants from TROG 03.04-RADAR trial were analysed. Relative (R1-R75 Gy) and absolute (A60-A75 Gy) bladder dose-surface area receiving more than a threshold dose and equivalent uniform dose using exponent a (range: aâ [1 ... 100]) were derived. The dose-symptom correlates were analysed using; peak-symptom (logistic), multiple-event (generalised estimating equation) and event-count (negative binomial regression) models. Results Stronger dose-symptom correlates were found for incontinence and frequency using multiple-event and/or event-count models. For dysuria and haematuria, similar or better relationships were found using peak-symptom models. Dysuria, haematuria and high grade (≥2) incontinence were associated to high dose (R61-R71 Gy). Frequency and low grade (≥1) incontinence were associated to low and intermediate dose-surface parameters (R13-R41 Gy). Frequency showed a parallel behaviour (a = 1) while dysuria, haematuria and incontinence showed a more serial behaviour (a = 4 to a ≥ 100). Relative dose-surface showed stronger dose-symptom associations. Conclusions For certain endpoints, the multiple-event and event-count models provide stronger correlates over peak-symptom models. Accounting for multiple events may be advantageous for a more complete understanding of urinary dose-symptom relationships.