Evaluation of transrectal ultrasound-based dosimetry for brachytherapy of prostate cancer: a single-center experience

PURPOSE: To explore the possibility of intraoperative transrectal ultrasound (TRUS)-based dose verification in transperineal brachytherapy (BT) with iodine-125 ((125)I) seeds for prostate cancer. MATERIAL AND METHODS: Fifteen patients with prostate cancer were treated using BT with (125)I seeds. Post-implant TRUS and computed tomography (CT) images were imported into treatment planning system (TPS) for dosimetry. Dosimetry parameters, including minimum dose received by 90% of the volume (D(90)), percentage of the volume receiving 100% of prescribed dose (V(100)), and percentage of the volume receiving 200% of prescribed dose (V(200)) were calculated based on TRUS and CT images, separately. The D(90) value of TRUS-based dosimetry was transformed to its expected value. Comparisons of the dosimetric parameters between post-operative verification and preoperative plans were made by paired t-test. One-way ANOVA model was used to assess the differences in preoperative plans. Agreements were evaluated between the preoperative planning and post-operative actual dose parameters using Bland-Altman analysis. RESULTS: In total, 825 of (125)I seeds were implanted successfully in 15 patients. In TRUS-based dosimetry, 674 seeds (81%) were identified clearly in TRUS-based images, and the expected value of D(90) parameter showed no significant differences compared with the preoperative planning and CT post-operation results (p > 0.05). In CT-based dosimetry, 810 seeds (98%) were identified clearly in CT-based images, and there was good consistency of D(90), V(100), and V(200) values (p > 0.05). Post-implant CT-based dosimetry indicated that (125)I seed implantation had fulfilled the expected plan. CONCLUSIONS: Intraoperative TRUS can be used for dosimetric verification of BT for prostate cancer.