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 (R(100)). Criteria for implant adequacy for both (103)Pd and (125)I included a prostate the percentage of the prostate volume covered by the prescription dose (V(100))>80%, a prostate the maximum dose covering 90% of the prostate volume (D(90)) of 90-140%, and an R(100)<1.0cm(3) for early (Day 0-7) dosimetry and <1.3cm(3) for late (Day 20-45) dosimetry. RESULTS: Mean prostatic volume was 35.1cm(3). The mean time from implant to CT scan was 29.9 days (range, 0-45 days). The respective mean overall prostate V(100) and D(90) were 89% and 101%, respectively, and remained consistent for sequence groups 1 through 6. Overall, the mean R(100) was 0.97+/-1.04cm(3). The R(100) was 1.15cm(3) for sequence Group 1 and with each subsequent sequence group decreased with a nadir of 0.83cm(3) 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, R(100) improved with increasing brachytherapist's experience, reaching a plateau after approximately 20 patients.
