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Intraoperative CBCT-Assisted Evaluation of Prostate Seed Implants: Ready for Primetime

G Cohen

G Cohen*, Y Hu , J Xiong , G Mageras , M Zelefsky , A Damato , Memorial Sloan-Kettering Cancer Center, New York, NY


TU-RPM-GePD-TT-3 (Tuesday, August 1, 2017) 3:45 PM - 4:15 PM Room: Therapy ePoster Theater

Purpose: We describe and validate a novel semi-automatic intraoperative implant evaluation using CBCT for TRUS-guided LDR prostate brachytherapy.

Methods: We implemented real-time CBCT-assisted post-implant evaluations prior to anesthesia reversal. Following intra-operative planning and seed deposition, a CBCT in lithotomy position with US probe in place is acquired. Image registration is performed by matching the TRUS probe in CBCT with a template CT image of the probe that was preregistered to the TRUS coordinates system. Intra-operatively planned seed coordinates were exported and transformed in CBCT frame-of-reference and used as a starting point for an algorithm searching sub-volumes of contiguous voxels with high Hounsfield units. Sub-volumes matching a single seed are listed as detected seeds; larger sub-volumes are listed as ‘likely seeds’, and left for the planner to accept, reject, or split into multiple seeds. CBCT seed coordinates are transformed into US space, and new contours are delineated on a newly acquired US scan. Seeds may be added based on assessment of the resulting isodoses and DVH. A series of ten recent consecutive cases has been reviewed retrospectively.

Results: For the 10 cases reviewed, an average of 97.8% (sd 2.25%) were detected; 95.4% (sd 3.74%) were detected directly and 2.41% (sd 3.16%) were listed as ‘likely’ seeds. Of the 5914 seeds implanted in all patients, 13 were not found by the software. In the clinical cases, these seeds were digitized manually by the planner. Intraoperative evaluation and implantation of additional seeds add 15-20 minutes to the overall procedure time.

Conclusion: We demonstrated that semi-automatic seed identification allows seed identification with a success rate of 97.8%, CBCT assisted intraoperative evaluation of prostate seed implants is an efficient tool to identify and correct suboptimal implant before reversal of anesthesia, and could potentially be used in lieu of Day 0 CT evaluation.

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