Author: Ioannis Androulakis, Jérémy Godart, Mischa Hoogeman, Inger-Karine K. Kolkman-Deurloo, Remi A. Nout, Robin Straathof, Henrike Westerveld, Myra van Laar 👨🔬
Affiliation: Department of BioMechanical Engineering, Delft University of Technology, 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:
In brachytherapy for gynaecological cancers using intracavitary applicators, implant reconstruction is commonly performed using applicator libraries. These libraries contain applicator geometry models as well as dwell position (DP) models defined in respect to the applicator geometry. Here we investigate whether an afterloader integrated electromagnetic tracking (AIEMT) system can be utilized to experimentally define and assess the DP model.
Methods:
Dwell positions in four sets of two configurations of the Elekta Venezia™ Advanced Gynaecological Applicator (22 mm ovoids/40 mm intrauterine and 26 mm ovoids/70 mm intrauterine) were measured using an Elekta Flexitron prototype afterloader with AIEMT. Multiple measurements were performed to define the reproducibility of both the AIEMT measurements and the applicator geometry. AIEMT-based DPs were compared against the manufacturer-specified (MS) DP model and a computed tomography (CT)-corrected DP model that uses CT imaging instead of channel centerline to define DPs in the intrauterine channel.
Results:
Excellent AIEMT measurement reproducibility of ≤0.3 mm was observed for both configurations. The overall reproducibility, including applicator geometric reproducibility, was ≤0.7 mm for both configurations. Large discrepancies from the MS-DP model were observed, with mean±2sd deviations of 1.1±1.3 mm (22/40) and 1.4±1.3 mm (26/70) for the whole applicator, 0.9±1.2 mm (22/40) and 0.9±0.7 mm (26/70) for ovoid, and 1.5±1.7 mm (22/40) and 1.9±1.4 mm (26/70) for intrauterine channels separately. Using the CT-corrected DP model as baseline reduced discrepancies to 0.9±0.8 mm (22/40) and 0.8±0.4 mm (26/70) for the whole applicator, 0.9±0.7 mm (22/40) and 0.8±0.8 mm (26/70) for ovoid, and 1.0±1.0 mm (22/40) and 0.8±0.4 mm (26/70) for intrauterine channels separately.
Conclusion:
This study confirms that AIEMT can reproducibly and accurately reconstruct source dwell positions in gynaecological brachytherapy applicators for commissioning and quality assurance purposes. AIEMT-based DP measurements agree more with measured DP models than MS DP models based on the channel centerline.