Purpose: To compare the results of intraoperative dosimetry with those of postimplant computed tomography (CT)-based dosimetry after 125I prostate brachytherapy. Methods and materials: We treated 412 prostate cancer patients with 125I prostate brachytherapy, with or without external beam radiotherapy at our institution. Neoadjuvant hormone therapy was administered to 331 patients (80.3%). Implantation was performed using an intraoperative interactive technique. Postimplant dosimetry was performed on Day 1 and Day 30 using CT imaging. The dosimetric results for the prostate, urethra, and rectum were compared among intraoperative ultrasound, and CT scans of Day 1 and Day 30. Results: The mean intraoperative minimal dose received by 90% of the prostate volume (D90) was 118.8% of the prescribed dose vs. 106.4% for Day 1 (p < 0.01) and 119.2% for Day 30 (p = 0.25). There were no significant correlations between the intraoperative D90 and the postimplant D90 values (intraclass correlation coefficients = 0.42 and 0.33 for Day 1 and Day 30, respectively). Prostatic edema at Day 1 had the largest effect on the Day 1 D90 (p < 0.01). The factor significantly affecting the Day 30 D90 was neoadjuvant hormone therapy (p < 0.01). The mean Day 30 D90 for the hormone-treated patients was 117.9%, compared with 124.6% for those who remained hormone naïve. The intraoperative and postimplant dosimetric values differed significantly for the urethra and rectum. Conclusions: Our results demonstrate that there are no significant differences between the D90 assessments obtained intraoperatively and at Day 30 postoperatively. Furthermore, there are no definite correlations between intra- and postimplantation dosimetric values. Other D90 values differed significantly between the intraoperative and postimplant dosimetry. This study suggests that dosimetry has negligible clinical utility for informing patients, at discharge, of whether or not their implants are adequate.
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