Urethral dosimetry and urinary symptoms after prostate brachytherapy: Analyzing key predictive factors

Urinary toxicity is a common side effect of prostate brachytherapy. This study evaluated the relationship between urethral dosimetry and urinary symptoms following low-dose prostate brachytherapy.

We retrospectively analyzed 175 patients who underwent I-125 prostate brachytherapy. Urethral contours were generated using MRI-TRUS fusion and transferred to day-30 CT scans. Dosimetric parameters were calculated for both rigid and deformed urethral models. Urinary symptoms were assessed using the International Prostate Symptom Score (IPSS) at baseline and 1 month after treatment. Correlations between dosimetric parameters and IPSS were analyzed.

Median IPSS increased from 4 at baseline to 9 at 1 month. Weak correlations were observed between 1-month IPSS and urethral volume, length, and V150 (volume receiving ≥150% of the prescribed dose). Patients with urethral V150 ≥0.61cc had significantly higher 1-month IPSS (mean difference 2.8 points, p = 0.001). In multivariate analysis, only baseline IPSS (p < 0.001) and prostate volume (p = 0.021) independently predicted 1-month IPSS. No dosimetric parameters predicted acute urinary retention.

Early urinary toxicity after prostate brachytherapy is multifactorial. Baseline urinary function and prostate volume were the strongest predictors, but maintaining low urethral V150 remains important to limit morbidity.