Correlations of post-implant regional dosimetric parameters at 24 hours and one month, with clinical results of low-dose-rate brachytherapy for localized prostate cancer

Purpose: To evaluate the correlations of post-implant regional dosimetrics at 24 hours (24 h) and 1 month after implant procedures, with clinical outcomes of low-dose-rate (LDR) brachytherapy for localized prostate cancer.

Material and methods: Between January 2008 and December 2014, 130 consecutive patients treated for localized prostate cancer, receiving definitive iodine-125 (¹²⁵I) brachytherapy treatment were retrospectively analyzed. All patients underwent post-implant CT imaging for dosimetric analysis at 24 h and 1 month after implantation procedure. Prostate contours were divided into quadrants: anterior-superior (ASQ), posterior-superior (PSQ), anterior-inferior (AIQ), and posterior-inferior (PIQ). Predictive factors and cut-off values of biochemical failure-free survival (BFFS) and toxicities of LDR brachytherapy were analyzed.

Results: The median follow-up time was 69.5 months. Seven patients (5.4%) had biochemical failure. The 3-year and 5-year BFFS rates were 96.7% and 93.1%, respectively. On multivariate analysis, prostate-specific antigen and Gleason score were significant prognostic factors for biochemical failure. D₉₀ (the minimal dose received by 90% of the volume) of PSQ and PIQ at 24 h, and D₉₀ of PSQ at 1 month were also significant factors. The cut-off values of PSQ D₉₀ were 145 Gy at 24 h and 160 Gy at 1 month. D₉₀ of the whole prostate was not significant at 24 h and at 1 month. D₉₀ of PSQ at 1 month was a significant factor for rectal hemorrhage.

Conclusions: Post-implant D₉₀ of PSQ is significantly associated with BFFS for localized prostate cancer not only at 1 month, but also at 24 hours. D₉₀ of PSQ at 1 month is also a significant factor for rectal hemorrhage.