Effects of pelvic rotation and needle angle on pubic arch interference during transperineal prostate implants

Purpose: Pubic arch interference due to an enlarged prostate gland or a nar row pubic arch is often a limiting factor in adequate prostate coverage dur ing transperineal brachytherapy. The purpose of this study was to evaluate the effects of both pelvic rotation and needle angles on pubic arch interfe rence using CT-based 3-D information. Methods and Materials: Seven patients had CT imaging in both supine and lit hotomy positions and 3-D treatment planning was performed with three needle angles (20 degrees downward, 0 degrees, 20 degrees upward). The pubic arch interference was then measured and comparisons were made for each needle t rajectory and pelvic position. Results: Increasing pelvic rotation from supine to lithotomy position shows less pubic arch interference. Directing the needle tip upward shows less p ubic arch interference in both supine and lithotomy positions when compared to needle tips directed downward. Conclusions: Both pelvic position and needle angles are important factors i nfluencing pubic arch interference. Preplanning CT-based 3-D information ma y assist for individualized treatment planning in patients with a significa nt bony interference, thus avoiding pubic arch interference during implanta tion. (C) 2000 Elsevier Science Inc.