ESTRO 2025 - Abstract Book

S394

Brachytherapy - Urology

ESTRO 2025

3797

Proffered Paper Electromagnetic tracking-based implant reconstruction in intraoperative prostate HDR-BT: implementation and retrospective evaluation on clinical data Ioannis Androulakis 1 , Jérémy Godart 1,2 , Miranda E.M.C. Christianen 1 , Henrike Westerveld 1 , Lorne Luthart 1 , Remi A. Nout 1 , Mischa S. Hoogeman 1,2 , Inger-Karine K. Kolkman-Deurloo 1 1 Department of Radiotherapy, Erasmus MC Cancer Institute, University Medical Center, Rotterdam, Netherlands. 2 Department of Medical Physics & Informatics, HollandPTC, Delft, Netherlands Purpose/Objective: In transrectal ultrasound (TRUS) based intraoperative prostate HDR-BT treatment planning, implant reconstruction is a laborious and error prone task [1]. It is known that afterloader-integrated electromagnetic tracking (AIEMT) is a reliable method for quality assurance and error detection of the implant reconstruction [2]. Electromagnetic tracking can also be employed directly for implant reconstruction, as has elsewhere been applied using manual measurements [3]. However, integration of AIEMT in the treatment planning system (TPS) is not yet available. In this study we developed a workflow that transforms AIEMT measurements in an implant reconstruction, and imports this in the TPS. The workflow was retrospectively implemented on clinical cases and the dosimetric differences in the delivered plan using the original clinical image-based or AIEMT-based reconstruction method was evaluated. Material/Methods: The AIEMT based reconstruction workflow consists of AIEMT measurements performed after needle implantation using a Flexitron investigational afterloading device with an integrated electromagnetic tracking sensor in the check cable (Elekta AB, Stockholm, Sweden). Along each implanted needle, the AIEMT sensor follows a predefined track measuring positions every 5 mm. The AIEMT measurements of each needle are used to calculate the coordinates of control points defining the needle reconstruction according to Figure 1. The reconstruction of all needles is then imported in the Oncentra-Prostate TPS by modifying the DICOM RT-plan.

For the retrospective evaluation, we used data from 14 patients for whom the implant was measured using AIEMT before the first fraction of intraoperative TRUS-based HDR-BT (part of 2x13.5Gy treatment). The dose distribution