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UBC Theses and Dissertations

Towards intra-operative dosimetry for prostate brachytherapy : improved seed detection and registration to ultrasound using needle detection Lobo, Julio


Errors in seed placement during low dose rate prostate brachytherapy can result in over-treating healthy tissue and/or under-treating cancer cells. In a standard treatment procedure, seeds are implanted according to a planned seed distribution. This pre-operative plan (pre-plan) is created using an ultrasound volume scan taken about two weeks earlier. Errors in seed placement can occur due to changes in prostate structure during those two weeks, and from seed displacement during and after the actual operation. This thesis presents methods of seed localization that are suitable for both postoperative and intra-operative use. The techniques can be applied to the imaging modalities used in the current operation setup to implement a method of intraoperative planning. This involves using Transrectal Ultrasound (TRUS) and C-arm X-ray Fluoroscopy (fluoro) data to monitor the seed positions relative to the current target volume during an operation. Towards this goal, an automatic method of assigning seeds to their corresponding insertion needle tracks has been developed to match seeds between modalities so that seed displacements can be computed. This method can be applied to measure intra-operative misplacement, by comparing the desired positions to the actual positions computed from fluoro data, or post-implant movement, comparing the fluoro seed positions to those from post-implant Computed Tomography (CT) data. For the intra-operative and post-implant data, 99.31% and 99.41% of the seeds were correctly assigned, respectively. An average intra-operative seed displacement of 4.94±2.42 mm and a further 2.97±1.81 mm of post-implant movement is measured. This information reveals several directional trends and can be used to preemptively correct the pre-operative plan (pre-plan).

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