Prostate cancer is the most diagnosed cancer among men. Many patients with localized prostate
cancer are treated with brachytherapy, one form of which involves permanent implantation of
approximately 100 radioactive sources into and sometimes immediately around the prostate
while the patient is anesthetized. During the procedure, transrectal ultrasound (TRUS) and
fluoroscopic images (acquired using a mobile C-arm fluoroscopic X-ray system) are used to
guide and visually assess implant quality, but do not provide accurate quantitative dosimetry.
Thus, the patient undergoes a CT scan after the implantation is completed for dosimetric
evaluation. However, this practice is not ideal as it occurs after the patient has left the operating
room, when there is no longer any opportunity to modify the implant, if required.
In this research project, a workflow was developed to assess the feasibility of performing
intraoperative dosimetry using two routinely available imaging systems (a cone beam CT
(CBCT) capable C-arm, and an ultrasound machine) for intraoperative dosimetric assessment of
permanent implant prostate brachytherapy. In the proposed methods, the locations of all
implanted sources were obtained from either 3D reconstructions of multiple planar radiographs,
or from CBCT images. They were then registered to prostate contours delineated on the TRUS
images, based on a common subset of sources identified on both image sets. In this process,
prostate contours were deformed, using a finite element model, to take into account the effect of
probe pressure in the TRUS images. Prostate dosimetric parameters obtained using this method
were in agreement with postimplant CT dosimetry results, considering the uncertainty associated
with each of these methods.
An algorithm for automatic detection of seeds on TRUS images using a convolutional neural
network was also developed during the course of this work. The model was trained to detect the
needle track first and then the individual sources within the needle track. This automated
approach outperformed a human observer in precision.
The results of the work described in this thesis support the conclusion that the proposed
dosimetry methods are feasible for real-time intraoperative dosimetric analysis of the implant
and can potentially also replace postimplant CT dosimetry.Science, Faculty ofPhysics and Astronomy, Department ofGraduat
