An MRI-based dose--reponse analysis of urinary sphincter dose and urinary morbidity after brachytherapy for prostate cancer in a phase II prospective trial.

ABSTRACT

PURPOSE: To compare dose-volume histogram variables for the internal and external urinary sphincters (IUS/EUS) with urinary quality of life after prostate brachytherapy. METHODS AND MATERIALS Subjects were 42 consecutive men from a prospective study of brachytherapy as monotherapy with (125)I for intermediate-risk localized prostate cancer. No patient received hormonal therapy. Preplanning constraints included prostate V100 higher than 95%, V150 lower than 60%, and V200 lower than 20% and rectal R100 less than 1cm(3). Patients completed the Expanded Prostate Cancer Index Composite quality-of-life questionnaire before and at 1, 4, 8, and 12 months after implantation, and urinary domain scores were analyzed. All structures including the IUS and EUS were contoured on T2-weighted MRI at day 30, and doses received were calculated from identification of seeds on CT. Spearman's (nonparametric) rank correlation coefficient (ρ) was used for statistical analyses. RESULTS: Overall urinary morbidity was worst at 1 month after the implant. Urinary function declined when the IUS V285 was 0.4% (ρ=-0.32, p=0.04); bother worsened when the IUS V35 was 99% (ρ=-0.31, p=0.05) or the EUS V240 was 63% (ρ=-0.31, p=0.05); irritation increased when the IUS V35 was 95% (ρ=-0.37, p=0.02) and the EUS V265 was 24% (ρ=-0.32, p=0.04); and urgency worsened when the IUS V35 was 99.5% (ρ=-0.38, p=0.02). Incontinence did not correlate with EUS or IUS dose. CONCLUSIONS: Doses to the IUS and EUS on MRI/CT predicted worse urinary function, with greater bother, irritative symptoms, and urgency. Incorporating MRI-based dose-volume histogram analysis into the treatment planning process may reduce acute urinary morbidity after brachytherapy.