Abstract
High-dose-rate (HDR) brachytherapy has become a popular treatment modality for localized prostate
cancer. Prostate HDR treatment involves placing 10 to 20 catheters (needles) into the prostate gland, and
then delivering radiation dose to the cancerous regions through these catheters. These catheters are often
inserted with transrectal ultrasound (TRUS) guidance and the HDR treatment plan is based on the CT
images. The main challenge for CT-based HDR planning is to accurately segment prostate volume in CT
images due to the poor soft tissue contrast and additional artifacts introduced by the catheters. To
overcome these limitations, we propose a novel approach to segment the prostate in CT images through
TRUS-CT deformable registration based on the catheter locations. In this approach, the HDR catheters
are reconstructed from the intra-operative TRUS and planning CT images, and then used as landmarks for
the TRUS-CT image registration. The prostate contour generated from the TRUS images captured during
the ultrasound-guided HDR procedure was used to segment the prostate on the CT images through
deformable registration. We conducted two studies. A prostate-phantom study demonstrated a submillimeter
accuracy of our method. A pilot study of 5 prostate-cancer patients was conducted to further
test its clinical feasibility. All patients had 3 gold markers implanted in the prostate that were used to
evaluate the registration accuracy, as well as previous diagnostic MR images that were used as the gold
standard to assess the prostate segmentation. For the 5 patients, the mean gold-marker displacement was
1.2 mm; the prostate volume difference between our approach and the MRI was 7.2%, and the Dice
volume overlap was over 91%. Our proposed method could improve prostate delineation, enable accurate
dose planning and delivery, and potentially enhance prostate HDR treatment outcome.
