Analysis of the Pro-Qura Database: Rectal dose, implant quality, and brachytherapist's experience

Abstract 

Purpose

This study analyzed rectal dosimetry outcomes of Pro-Qura proctored implants to assess the achievability of proposed rectal dose constraints in the setting of standardized pre- and postimplant dosimetry in community-based brachytherapy programs.

Methods and materials

From August 2005 to July 2007, 713 postimplant CT scans were evaluated from 26 brachytherapists actively participating in Pro-Qura. Postimplant dosimetry was performed in a standardized fashion. The entirety of the rectal wall was contoured and evaluated for dose. Rectal dose was defined in terms of the volume of the rectum receiving 100% of the prescription dose (R₁₀₀). Criteria for implant adequacy for both ¹⁰³Pd and ¹²⁵I included a prostate the percentage of the prostate volume covered by the prescription dose (V₁₀₀)>80%, a prostate the maximum dose covering 90% of the prostate volume (D₉₀) of 90–140%, and an R₁₀₀<1.0cm³ for early (Day 0–7) dosimetry and <1.3cm³ for late (Day 20–45) dosimetry.

Results

Mean prostatic volume was 35.1cm³. The mean time from implant to CT scan was 29.9 days (range, 0–45 days). The respective mean overall prostate V₁₀₀ and D₉₀ were 89% and 101%, respectively, and remained consistent for sequence groups 1 through 6. Overall, the mean R₁₀₀ was 0.97±1.04cm³. The R₁₀₀ was 1.15cm³ for sequence Group 1 and with each subsequent sequence group decreased with a nadir of 0.83cm³ in sequence Group 6 (p=0.22). Rectal dosimetry was deemed inadequate in 39% of Group 1 implants but only 22% in Group 6 (p=0.016). The reduced rectal doses did not impact prostate gland coverage.

Conclusions

Using standardized dosimetry, R₁₀₀ improved with increasing brachytherapist's experience, reaching a plateau after approximately 20 patients.

Keywords: Prostate brachytherapy, Quality, Dosimetry, Rectal dose