Author: Ioannis Androulakis, Miranda E.M.C. Christianen, Jérémy Godart, Mischa Hoogeman, Inger-Karine K. Kolkman-Deurloo, Lorne Luthart, Remi A. Nout, Henrike Westerveld 👨🔬
Affiliation: Department of Radiotherapy, Erasmus MC Cancer Institute, University Medical Center, Rotterdam, The Netherlands, Department of Radiotherapy, Erasmus MC Cancer Institute, University Medical Center Rotterdam 🌍
Purpose:
Despite the advantages of transrectal ultrasound-based treatment planning for HDR prostate cancer brachytherapy which allows on-line treatment delivery in the intraoperative setting, it is known that ultrasound-based implant reconstruction is error-prone. Therefore we aim to create a setup and workflow that allows automated implant reconstruction using a Flexitron afterloader prototype with integrated electromagnetic tracking (EMT) (Elekta AB, Stockholm, Sweden) and Oncentra Prostate (OCP) (Elekta AB, Stockholm, Sweden) treatment planning system.
Methods:
To align the EMT measurement coordinate system with the coordinate system in OCP, a 6DoF EMT reference sensor, detecting position and orientation relative to the EMT field generator, was integrated into the template holder at a stable and known position. Automatic EMT measurements on 11 dwell positions along each needle were performed by the afterloader and registered to the OCP coordinate system. These measurements were used to define each needle reconstruction. The implant reconstruction was then imported in OCP for treatment planning.
For testing we used a setup with an ultrasound prostate phantom (053S, CIRS INC, USA) with four flexible needles positioned in a rectangular geometry, ensuring good TRUS imaging conditions. We assessed the reproducibility of the EMT-based implant reconstruction over 5 measurements by calculating the variability of the active dwell positions in the target region using two standard deviations (sd). The agreement between EMT-based and image-based implant reconstructions was evaluated by comparing the same dwell positions.
Results:
Reconstruction reproducibility for dwell positions in the target region was 0.5 mm. Mean(±2sd) agreement between the two reconstruction methods, expressed by Euclidean distance of corresponding dwell positions in the target region, was 0.7(±0.4) mm.
Conclusion:
We successfully developed and validated a method to integrate EMT-based implant reconstruction in the OCP treatment planning workflow. This advancement has the potential to automate the implant reconstruction process and improve the implant reconstruction quality.