Permanent prostate brachytherapy: Dosimetric results and analysis of a learning curve with a dynamic dose-feedback technique

Abstract

Purpose: A permanent prostate brachytherapy (PPB) program utilizing intraoperative inverse-planned dynamic dose-feedback was initiated without prior firsthand experience of alternative techniques. The purpose of this study is to assess the dosimetric learning curve associated with this approach.

Methods and materials: A total of 77 patients underwent PPB implants as monotherapy for localized prostate cancer to a prescription dose of 145 Gy with loose 125I seeds between December 2003 and June 2004. Intraoperative and postoperative dosimetric values, total implanted radioactivity, and operating room (OR) times were compared by sequential case number for all cases.

Results: The median intraoperative dosimetric values were: D90 (the minimum dose to 90% of the prostate) = 170 Gy (range, 135-203 Gy), V100 (the volume of the prostate that receives 100% of the prescription dose) = 96% (range, 86-100), V150 = 66% (range, 34-86). Median postoperative dosimetric values were as follows: D90 = 168 Gy (range, 132-197 Gy), V100 = 95% (range, 86-99), V150 = 74% (range, 51-84). Median implanted activity was 0.79 mCi per cubic centimeter of prostate (range, 0.541-1.13). There was no significant correlation by case number on any postoperative dosimetric parameter studied. Door-to-door OR time was reduced from median 138 to 97.5 min per case at the end of the series with a correlation coefficient of -0.76 for the initial 28 cases.

Conclusion: Satisfactory dosimetric parameters can be achieved from the outset without a learning curve effect in an appropriately trained environment. The learning curve for dynamic dose-feedback PPB in a clinic naïve to other techniques is apparent in terms of OR time.