To evaluate adaptive planning for permanent prostate brachytherapy and to identify the prostate regions that needed adaptation.Methods and materials
After the implantation of stranded seeds, using real-time intraoperative planning, a transrectal ultrasound (TRUS)-scan was obtained and contoured. The positions of seeds were determined on a C-arm cone-beam computed tomography (CBCT)-scan. The CBCT-scan was registered to the TRUS-scan using fiducial gold markers. If dose coverage on the combined image-dataset was inadequate, an intraoperative adaptation was performed by placing remedial seeds. CBCT-based intraoperative dosimetry was analyzed for the prostate (DSymbol, VSymbol, and VSymbol) and the urethra (DSymbol). The effects of the adaptive dosimetry procedure for Day 30 were separately assessed.Results
We analyzed 1266 patients. In 17.4% of the procedures, an adaptation was performed. Without the dose contribution of the adaptation Day 30 VSymbol would be < 95% for half of this group. On Day 0, the increase due to the adaptation was 11.8 ± 7.2% (1SD) for DSymbol and 9.0 ± 6.4% for VSymbol. On Day 30, we observed an increase in DSymbol of 12.3 ± 6.0% and in VSymbol of 4.2 ± 4.3%. For the total group, a DSymbol of 119.6 ± 9.1% and VSymbol of 97.7 ± 2.5% was achieved. Most remedial seeds were placed anteriorly near the base of the prostate.Conclusion
CBCT-based adaptive planning enables identification of implants needing adaptation and improves prostate dose coverage. Adaptations were predominantly performed near the anterior base of the prostate.