Computed tomography–ultrasound fusion brachytherapy: Description and evolution of the technique

Purpose In this manuscript, we describe our computed tomography (CT)–ultrasound (US) fusion prostate brachytherapy method and report the updated dosimetry result and trend. Methods and materials This cohort of 132 consecutive patients received CT–US fusion prostate brachytherapy from the first author (DBF) from December 2002 to August 2006. The technique consists of a hybrid preplanned and intraoperative dynamic dosimetry method, which initially delivers a standard preplanned source distribution, and then uses interval CT-based source identification dosimetry, fused to an identically spaced intraoperative US volume study series, to direct remedial sources that correct initial dosimetry deficiencies. Results The median and minimum prostate Day 0 prostate volume of interest receiving 100% of prescribed dose (V100) results in this patient cohort measured 98.26% and 92.61%, respectively, with all Day 0 prostate dose received by 90% of the volume of interest (D90) results exceeding 100% of the prescribed dose, and the maximum Day 0 prostate D90 value measuring 128% of the prescribed dose. During the period of this analysis, a trend to the decreased quantity of dynamic remedial millicuries per case was identified, with the total sources decreasing from 116% to 106% of the preplanned level, resulting in minimal V100 and D90 decreases, while continuing to exceed the minimum Day 0 dosimetry requirements. Conclusions CT–US fusion dynamic prostate brachytherapy represents a consistent prostate brachytherapy dosimetry delivery mechanism, creating a tight lower and upper bound to the final Day 0 prostate V100 and D90 parameters. The practice and pitfalls of this technique are discussed in detail.