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: a∈[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.