Dosimetric coverage of the prostate, normal tissue sparing, and acute toxicity with high-dose-rate brachytherapy for large prostate volumes.

PURPOSE To evaluate dosimetric coverage of the prostate, normal tissue sparing, and acute toxicity with HDR brachytherapy for large prostate volumes. MATERIALS AND METHODS One hundred and two prostate cancer patients with prostate volumes >50 mL (range: 5-29 mL) were treated with high-dose-rate (HDR) brachytherapy ± intensity modulated radiation therapy (IMRT) to 4,500 cGy in 25 daily fractions between 2009 and 2013. HDR brachytherapy monotherapy doses consisted of two 1,350-1,400 cGy fractions separated by 2-3 weeks, and HDR brachytherapy boost doses consisted of two 950-1,150 cGy fractions separated by 4 weeks. Twelve of 32 (38%) unfavorable intermediate risk, high risk, and very high risk patients received androgen deprivation therapy. Acute toxicity was graded according to the Common Terminology Criteria for Adverse Events (CTCAE) version 4. RESULTS Median follow-up was 14 months. Dosimetric goals were achieved in over 90% of cases. Three of 102 (3%) patients developed Grade 2 acute proctitis. No variables were significantly associated with Grade 2 acute proctitis. Seventeen of 102 (17%) patients developed Grade 2 acute urinary retention. American Urological Association (AUA) symptom score was the only variable significantly associated with Grade 2 acute urinary retention (p=0.04). There was no ≥ Grade 3 acute toxicity. CONCLUSIONS Dosimetric coverage of the prostate and normal tissue sparing were adequate in patients with prostate volumes >50 mL. Higher pre-treatment AUA symptom scores increased the relative risk of Grade 2 acute urinary retention. However, the overall incidence of acute toxicity was acceptable in patients with large prostate volumes.