Phase II study of intraoperative dosimetry for prostate brachytherapy using registered ultrasound and fluoroscopy.

PURPOSE: To assess the performance of a system of intraoperative dosimetry and obtain estimates of dosimetry outcomes achieved when utilizing the system in a Phase II clinical trial.

METHODS AND MATERIALS: Forty-five patients undergoing permanent Pd-103 seed implantation for prostate cancer were prospectively enrolled. Seed implantation was performed and dose was tracked intraoperatively using intraoperative registered ultrasound and fluoroscopy (iRUF). Three-dimensional seed locations were computed from X-rays and registered to ultrasound for intraoperative dosimetry, followed by adaptive plan modification to achieve prostate V100 ≥95% and ≥95% D90. Time required for iRUF was recorded. Postoperative CT/MRI scans were performed 1 day after the implantation and used as reference for dosimetric analysis. Dosimetric parameters for the prostate and urethra were compared between standard ultrasound-based dosimetry (USD), iRUF, and postoperative CT/MRI.

RESULTS: Mean total time for iRUF was <30 min. A mean of four seeds (0-12) were added per implant to correct cold spots discovered by iRUF. Day 1 CT/MRI prostate V100 was ≥95% for 44/45 patients; 1 patient had Day 1 V100 93%. No patient had rectal V100 exceeding 1 cc. Compared to CT/MRI, iRUF dosimetry had significantly smaller mean differences and higher correlations for all prostate and urethral dosimetric parameters examined than USD. Both USD and iRUF tended to overestimate dose, but with less bias in iRUF than USD.

CONCLUSIONS: Intraoperative dosimetry utilizing iRUF was associated with acceptable increase in procedure time and enabled very high rates of achieving excellent prostate dose coverage. iRUF intraoperative dosimetry approximated postoperative CT/MRI dosimetry to a greater degree than USD for the prostate and urethra.