Predictors of urinary morbidity in Cs-131 prostate brachytherapy implants

Cesium-131 is a newer radioisotope being used in prostate brachytherapy (PB). This study was conducted to determine the predictors of urinary morbidity with Cs-131 PB.

A cohort of 159 patients underwent PB with Cs-131 at our institution and were followed by using Expanded Prostate Cancer Index Composite (EPIC) surveys to determine urinary morbidity over time. EPIC scores were obtained preoperatively and postoperatively at 2 and 4 weeks, and 3 and 6 months. Different factors were evaluated to determine their individual effect on urinary morbidity, including patient characteristics, disease characteristics, treatment, and dosimetry. Multivariate analysis of covariance was carried out to identify baseline determinants affecting urinary morbidity. Factors contributing to the need for postoperative catheterization were also studied and reported.

At 2 weeks, patient age, dose to 90% of the organ (D90), bladder neck maximum dose (D(max)), and external beam radiation therapy (EBRT) predicted for worse function. At 4 weeks, age and EBRT continued to predict for worse function. At the 3-month mark, better preoperative urinary function, preoperative alpha blockers, bladder neck D(max), and EBRT predicted for worse urinary morbidity. At 6 months, better preoperative urinary function, preoperative alpha blockers, bladder neck D(max), and EBRT were predictive of increased urinary problems. High bladder neck D(max) and poor preoperative urinary function predicted for the need for catheterization.

The use of EBRT plus Cs-131 PB predicts for worse urinary toxicity at all time points studied. Patients should be cautioned about this. Age was a consistent predictor of worsened morbidity immediately following Cs-131 PB, while bladder D(max) was the only consistent dosimetric predictor. Paradoxically, patients with better preoperative urinary function had worse urinary morbidity at 3 and 6 months, consistent with recently published literature.