Integrating automated electromagnetic tracking-based needle reconstruction in the intraoperative high-dose-rate prostate brachytherapy workflow

Background and Purpose: Manual transrectal ultrasound (TRUS) reconstruction, currently used in intraoperative prostate brachytherapy, is error‑prone. Automated implant reconstruction with electromagnetic tracking (EMT) has the potential to improve accuracy. The aim of this study was to implement and validate afterloader‑integrated EMT for automated implant reconstruction. Materials and Methods: An afterloader prototype equipped with an integrated EMT system was used in conjunction with a TRUS-based treatment planning system and setup. A workflow was developed to transform the EMT measurements into the implant reconstruction and import this into the treatment planning software. The workflow was retrospectively evaluated using clinical data from 14 patients. To align the EMT measurements with the treatment-planning coordinate system without a TRUS-based pre-reconstruction, a novel setup was developed using a single reference sensor integrated into the template holder. The reproducibility and accuracy of the workflow using this latter setup was evaluated in phantom measurements. Results: The retrospective evaluation revealed that errors in active dwell positions of up to 10.2 mm caused absolute V_100% differences of up to 5.3 % of the target volume, and up to 24.4 %, 2.1 %, and 14.1 % of the prescribed dose for urethra D_0.1cm3, rectum D_2cm3, and bladder D_1cm3, respectively. In phantom measurements with our novel setup using reference sensor registration, EMT-based reconstruction demonstrated high reproducibility (0.5 mm) and agreement with TRUS-based reconstruction (0.7 mm), requiring a measurement time of < 23 s per implanted needle. Conclusion: The implementation of EMT-based reconstruction on clinical data shows clinically relevant impact on dose-volume metrics of TRUS-based implant reconstructions errors. Using the novel workflow and hardware, highly accurate and automated implant reconstruction is possible.