BERKELEY, CA (UroToday.com) - Permanent prostate brachytherapy (PPB) with 125I or 103Pd is a well established treatment for localized prostate cancer. Urinary morbidity, including possible acute urinary retention in 6-34%, is an important problem. Though urethral dose constraints are also recommended in guidelines, data correlating urethral dose with toxicity have only rarely been reported in the literature. The aim of this study was to evaluate possibly predictive factors on acute and late urinary quality of life changes after PPB.
| "...placement of sources with a minimum distance of a few mm to the urethra (5mm has been shown to be a reasonable threshold according to the results of this study) should be a major aim to avoid urinary morbidity." |
59 patients were surveyed prospectively before treatment (A), one month after (B) and >one year after PPB (C) using a validated questionnaire (Expanded Prostate Cancer Index Composite). The urinary domain comprises 12 items for function and bother. The multi-item scale scores were transformed lineary to a 0-100 scale, with higher scores representing better quality of life. Computed tomography (CT) postimplant scans were performed at days 1 (Foley catheter in situ) and 30 after PPB and sources within 5mm of the urethra at day 1 were identified. The prescription dose to the periphery of the prostate was 145Gy.
As opposed to the urethral dose-volume histogram, a larger number of sources within 5mm of the urethra at day 1 predicted significantly larger urinary bother score changes at times B and C – with an impact on incontinence and frequency (e.g. moderate/big problem with leaking urine in 25% vs. 3%, p=0.02; moderate/big problem with frequent urination in 33% vs. 7%, p<0.01, at time C with vs. without ≥3 sources in a single strand placed close to the urethra). In a multivariate analysis assessing problems more than one year after treatment, ≥three sources in single strand close to the urethra were independently predicting for moderate/big problem with leaking urine (HR, hazard ratio, 29; p=0.03) and frequent urination (HR 7.0; p=0.02). Day 30 prostate D90>175Gy predicted for moderate/big problem with pain on urination (HR 6.2; p=0.04).
Focusing on the urethral dose to different parts of the urethra, the only relevant tendency resulted for the impact of the dose to the lower urethra on the bother score worsening at time C (p=0.11/p=0.09 comparing lower urethra D10/D1).
Local trauma and local tissue irritation appears to be more important in comparison to a high local radiation dose. Though the dose to the urethra can also be a surrogate of the source distance to the urethra and certainly needs to be considered in the treatment planning process, placement of sources with a minimum distance of a few mm to the urethra (5mm has been shown to be a reasonable threshold according to the results of this study) should be a major aim to avoid urinary morbidity.
Written by:
Michael Pinkawa, MD as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.
