Prostatic conformal brachytherapy: 125I/103Pd postoperative dosimetric analysis.

Abstract

Widespread replication of the favorable long-term results of prostatic conformal brachytherapy achieved by the Seattle group requires evidence that the technical quality of their implants is achievable elsewhere. Preplanning with a modified uniform loading algorithm using low activity seeds produces virtually no regions within the planning volume at less than the prescribed dose and no interconnected volumes between seeds at double the dose. The operative procedure stabilizes the prostate and locates the prostate targets, needles, and seeds and their relationship to the bladder and rectum using transverse and longitudinal ultrasound as well as contrast enhanced fluoroscopy. A detailed postoperative dosimetric analysis of patients with clinical T1/T2 adenocarcinoma of the prostate gland who underwent transperineal ultrasound conformal prostatic brachytherapy from March through June 1996 was performed. The analysis involved 7 consecutive patients implanted with 125I seeds and 5 consecutive patients implanted with 103Pd seeds. Median coverage to the full minimal peripheral dose (mPD) was 96% (range 80-99%) of the prostate volume. At 80% of the mPD, median isodose coverage was 100% (range 91-100%) of the prostate volume. Regarding hot spots to critical structures, the median maximal urethral dose was 175% of the mPD (range 115-227%) and the median maximal dose to the anterior rectal mucosa was 105% of the mPD (range 83-133%). Analysis of postoperative dose-volume histograms has shown that our maximal dose surface to any volume greater than 5 cm3 is 203% (range 175-247%). These results indicate that good quality transperineal ultrasound prostatic conformal brachytherapy can be accurately reproduced in a community hospital setting and that biochemical no evidence of disease (NED) results and local control rates will be comparable to those of the Seattle group with no unexpected urethral or rectal complications or side effects.