Intra-operative Use of C-arm Cone-beam CT for Quality Assurance of Low-dose-rate Prostate Brachytherapy Dose Delivery
The investigators will assess the feasibility of intraoperative use of C-arm cone-beam CT
imaging for intraoperative dosimetric evaluation in prostate low-dose-rate (LDR)
brachytherapy. Patients recruited are those who will receive standard LDR brachytherapy for
prostate cancer treatment. Consenting patients will undergo additional 3D C-arm cone-beam CT
imaging (3D C-arm) and motorized trans-rectal ultrasound (TRUS). Volumetric and dosimetric
measures will be compared to those using the standard Day-0 CT images. The investigators
hope that the intraoperative 3D C-arm provides quality assurance measures sufficient to
eliminate the need for Day-0 CT LDR brachytherapy and provide the opportunity for
intraoperative modification of seed delivery plan.
Standard post-implant quality assessment at the BC Cancer Agency involves a pelvic CT 2-3 hours after treatment. This scan is performed outside the operating room, in a different location. As a result, it is not possible to receive immediate feedback on the quality of treatment. Furthermore, soft tissue visualization is poor in CT imaging and contouring variability is large. The use of other imaging modalities such as ultrasound would be beneficial. However, since the scan is performed at a different time, and with the patient in a different position, registering the images would be challenging.
Intra-operative C-arm CT imaging would provide immediate feedback on the quality of treatment, provide the opportunity of using information from intra-operative ultrasound imaging for soft tissue visualization, and eliminate the need for a separate scan in a different location.
Patients who are receiving low-dose-rate brachytherapy and consent to participate will undergo the additional imaging interventions described in section 5.7 of the application.
Patients will also undergo a pelvic CT as the standard of care.
To limit patient exposure to additional radiation dose, the investigators will divide the participants into 3 groups, each of which will receive a portion of the abovementioned scans. Details are described in the attached protocol.
Seed locations will be identified on the 3D C-arm volume. The prostate volume on the TRUS images will be delineated and the contours will be mapped onto the 3D C-arm volume to compute standard dosimetric parameters (V100, D90). Seeds and contours will be outlined on the corresponding Day-0 CT and standard dosimetric parameters will be computed. Day-0 CT will be contoured by multiple observers to compute variability in the resulting dosimetric parameters. Dosimetric values from the 3D C-arm will be compared to those of Day-0 CT and their intra-observer variability.
The seeds will be identified on 3D C-arm volumes with the TRUS probe inserted and retracted to create two seed clouds. Corresponding seeds will be matched. The difference between the seed locations in the two seed clouds will be used to model the prostate deformation due to the presence and absence of the TRUS probe.
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