Correlation of pre-implant computed tomography pubic arch study with postimplant dosimetry

Pubic arch interference is a common problem encountered during permanent implantation of prostate cancer. Pubic arch interference may be assessed by pelvic computed tomography (CT) scanning or by transrectal ultrasound (TRUS) imaging at the time of volume study. In this article, we present our experience with intraoperative pubic bone interference encountered in 23 consecutive patients with pre-implant CT-based 1 cm or less overlap of gland by pubic arch. Before implantation, the median pubic bone overlap in the anterior part of the gland was 2 mm (range,-11 to +6 mm), and the median pubic arch overlap in the lateral aspect of the gland was 5mm (range, 0 to 10 mm). During implantation, eight (0.95%) of 845 needles in four patients (17%) required repositioning of needles due to pubic arch interference. The median percentage postimplant volume of the gland receiving 144 Gy was 85% (range, 80% to 93%) based on postimplant CT dosimetry performed two to five days after implantation. In conclusion, a criterion of 1 cm or less gland overlap by bone on pre-implant CT scan is a simple, quick, and accurate predictor of significant pubic arch interference at the time of implantation. Based on good CT and TRUS correlation of prostate volume and pubic arch anatomy, the results of this study could be applicable to pubic arch studies performed by either TRUS or CT scanning.