Comparison between postoperative TRUS-CT fusion with MRI-CT fusion for postimplant quality assurance in prostate LDR permanent seed brachytherapy.

PURPOSE/OBJECTIVE Permanent seed Low-Dose-Rate brachytherapy is planned and delivered using transrectal ultrasound (TRUS). Post-implant evaluation for quality assurance is usually performed using Computed Tomography (CT). Registration of the CT images with MRI reduces subjectivity in contouring by improving prostate edge detection. We hypothesized that a set of TRUS images post procedure may provide the same benefit. MATERIAL/METHODS Consecutive patients undergoing Low-Dose-Rate prostate brachytherapy were recruited. TRUS images were recorded under anesthesia at completion of their implant. In addition, all patients underwent standard post-implant quality assurance including prostate CT and MRI at day 30. These were co-registered, contoured and seeds were identified. Three independent observers contoured and registered the post implant TRUS images to the Day 30 CT using seed matching. Prostate volumes and dosimetric parameters were compared through Intraclass Correlation Coefficient (ICC) to evaluate the concordance between MRI and ultrasound (US). RESULTS 26 patients were recruited from 10/17 to 01/18. Mean prostate volume was 34.5 (SD 10.8) cm at baseline on planning TRUS images, 37.4 (SD 11.3) cm on Day 0 post implant TRUS and 36.7 (SD 11.7) cm on Day 30 MRI. D90 was 112.6% (SD 9.3) on CT-MRI and 112.9% (SD 11.1) on CT-US. V100 was 94.6% (SD 3.8) for CT-MRI, 95.1% (SD 4.3) for CT-US. Student t-tests were used to compare groups. No significant differences were noted. CONCLUSION Post implant TRUS may be useful for quality assurance for post-implant dosimetry particularly if access to an MRI is limited.