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 (¹²⁵I) seeds for prostate cancer.

Material and methods: Fifteen patients with prostate cancer were treated using BT with ¹²⁵I 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 (D₉₀), percentage of the volume receiving 100% of prescribed dose (V₁₀₀), and percentage of the volume receiving 200% of prescribed dose (V₂₀₀) were calculated based on TRUS and CT images, separately. The D₉₀ 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 ¹²⁵I 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 D₉₀ 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 D₉₀, V₁₀₀, and V₂₀₀ values (p > 0.05). Post-implant CT-based dosimetry indicated that ¹²⁵I seed implantation had fulfilled the expected plan.

Conclusions: Intraoperative TRUS can be used for dosimetric verification of BT for prostate cancer.