Interactive tool for visualization and segmentation of permanent radioactive seeds in postoperative prostate brachytherapy CT images

Implantation of radioactive isotopes within the prostate for the treatment of early stage localized prostate cancer is becoming a popular treatment option. Postoperative calculation of the dose delivered to the prostate requires accurate verification of the number and location of seeds within the prostate. Current post operative dosimetry technique requires the dosimetrist to manually count and record the position of each seed from x-ray computed tomography (CT) images. This procedure is operator-dependent and time-consuming, thus limiting the ability of different brachytherapy centers to compare results and create a standard methodology. Seed identification is performed by thresholding the CT images interactively, using a graphical user interface, followed by mathematical morphology to remove noise. Segmented seeds are grouped into regions via connected-component analysis. Regions are then classified into seeds using a prior knowledge of the seed dimensions and their relative positions in the consecutive CT images. Unresolved regions, which can indicate the presence of more than one seed, are corrected manually. The efficiency of this tool was evaluated by comparing the time to manually count the seeds to the time required to do the same task using the automated program. For 15 sets of images from 15 patients, the average time for manually counting the seeds was 45 minutes per patient versus 6.4 minutes on average per patients, the average time for manually counting the seeds was 45 minutes per patient versus 6.4 minutes on average per patient when the software was used to perform the same task. Using the interactive visualization and segmentation algorithm, the time required to count the seeds during post- implant dosimetry has been reduced by a factor of 7 compared to the existing manual technique.