Impact of neoadjuvant androgen deprivation therapy on postimplant prostate D90 and prostate volume after low-dose-rate brachytherapy for localized prostate cancer

Objective Higher quality of postimplant dosimetric evaluation is associated with higher biochemical recurrence-free survival rates after low-dose-rate brachytherapy for localized prostate cancer. Postimplant prostate D90 is a key dosimetric parameter showing the quality of low-dose-rate brachytherapy. In this study, to improve the quality of low-dose-rate brachytherapy for localized prostate cancer, we investigated pre-implant factors affecting the reduction of postimplant prostate D90. Methods A total of 441 patients underwent low-dose-rate brachytherapy monotherapy and 474 patients underwent low-dose-rate brachytherapy with external beam radiation therapy. Logistic regression analysis was carried out to identify predictive factors for postimplant D90 decline. The cut-off value of the D90 decline was set at 170 Gy and 130 Gy in the low-dose-rate brachytherapy monotherapy group and low-dose-rate brachytherapy with external beam radiation therapy group, respectively. Results On multivariate analysis, neoadjuvant androgen deprivation therapy was identified as an independent predictive factor for the decline of postimplant D90 in both the low-dose-rate brachytherapy monotherapy group (P < 0.001) and low-dose-rate brachytherapy with external beam radiation therapy group (P = 0.003). Prostate volume changes and computed tomography/transrectal ultrasound prostate volume ratio were significantly and negatively correlated with the postimplant D90. The prostate volume changes and computed tomography/transrectal ultrasound prostate volume ratio were significantly higher in patients with neoadjuvant androgen deprivation therapy than those without neoadjuvant androgen deprivation therapy (P < 0.001). Conclusions Neoadjuvant androgen deprivation therapy decreased postimplant D90 with substantial prostate gland swelling after low-dose-rate brachytherapy. When neoadjuvant androgen deprivation therapy is required to reduce prostate volume for patients with large prostate glands and offer adequate local control for patients with high-risk prostate cancer before low-dose-rate brachytherapy, intraoperative D90 adjustment might be necessary.