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.