Inverse automated treatment planning with and without individual optimization in interstitial permanent prostate brachytherapy with high- and low-activity 125I.

Abstract

To determine whether dose distribution achieved with treatment plans using high- and low-activity (125)I implants differs. Based on intraoperative transrectal ultrasound scans of 71 patients, inverse automated treatment plans (IATP) were performed with 15.5-kBq (0.42-mCi) and 25.2-kBq (0.68-mCi) (125)I implants using a commercial 3-D planning system (Variseed). A prescription dose of 145 Gy in 98% of the prostate volume (V100), a maximum dose to the urethra of 250 Gy (D1), and a maximum dose to 10% of the anterior rectal wall of 145 Gy (D10) were required. The plans were manually corrected, if necessary. In the IATP, a better dose coverage of the prostate was found for high-activity seeds (V100 of 98% vs 84%). The prostate dose values increased with the prostate volume. After manual optimization, the differences were only marginal with a prostate V100 of 99% for both activities, a urethra D1 of 247 Gy and 239 Gy, and a rectum D10 of 135 Gy and 124 Gy for high- and low-activity seeds. Low-activity seeds required more sources (66 vs 47) and needles (24 vs 17; all numbers are median values). Concerning the prostate dose coverage, high-activity seeds are superior in the IATP. After manual adjustment, the dose values for the prostate and the organs at risk are similar. Considering a supposedly decreased toxicity and a shorter implantation time for a lower number of seeds, we recommend high-activity seeds for experienced teams.