Late urinary morbidity with high dose prostate brachytherapy as a boost to conventional external beam radiation therapy for local and locally advanced prostate cancer

Purpose: Late urinary retention (UR) is a known complication that may occur when using high dose rate brachytherapy (HDR-B) to boost external beam radiation therapy (EBRT) when treating prostate cancer. However, the dosimetric, treatment and clinical factors associated with this complication are not well-known. Materials and Methods: From March 1997 to March 2000 a total of 108 patients with local or locally advanced prostate adenocarcinoma were treated with EBRT (45 Gy) and HDR-B as a boost, when 16 to 20 Gy was given in 4 fractions twice daily. Median patient age was 68 years and median followup was 44 months (range 36 to 72). Each implant was performed using 8 to 18 needles with a median active length of 3 cm. Planning ultrasound target volume ranged from 23 to 65 cc. Results: Biological effective doses for the urethral region ranged from 107 to 138 Gy(3) (median 113). Crude and 5-year actuarial UR-free survival were 95.4% and 86.2%, respectively. Predictive factors for UR on univariate analysis were age more than 65 years (p = 0.0416), planning ultrasound target volume greater than 35 cc and active length of needles more than 3.5 cm (p = 0.0158). On multivariate analysis by Cox regression age was the only predictive factor (p = 0.027). Conclusions: HDR-B appears to offer a safe, reproducible and effective method of boosting conventional EBRT in patients with locally advanced prostate cancer. Results with this technology reveal late urinary morbidity rates paralleling those achieved with other forms of treatment, but further long-term followup is still needed to warrant a definitive conclusion.