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Session: Poster session 2 (Odd numbers)
Session starts: Friday 27 January, 10:00
Presentation starts: 10:00

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Robin Straathof (Delft University of Technology, BioMechanical Engineering, Delft, The Netherlands)
Jaap Meijaard (Delft University of Technology, Precision and Microsystems Engineering, Delft, The Netherlands)
Sharline van Vliet-Pérez (Erasmus University Medical Center, Radiotherapy, Rotterdam, The Netherlands)
Inger-Karine Kolkman-Deurloo (Erasmus University Medical Center, Radiotherapy, Rotterdam, The Netherlands)
Remi Nout (Erasmus University Medical Center, Radiotherapy, Rotterdam, The Netherlands)
Ben Heijmen (Erasmus University Medical Center, Radiotherapy, Rotterdam, The Netherlands)
Linda Wauben (Delft University of Technology, BioMechanical Engineering, Delft, The Netherlands)
Jenny Dankelman (Delft University of Technology, BioMechanical Engineering, Delft, The Netherlands)
Nick van de Berg (Delft University of Technology, BioMechanical Engineering, Delft, The Netherlands)

Abstract:
ABSTRACT Purpose In brachytherapy (BT) for cervical cancer, a radioactive source is driven by cable through an intracavitary (IC) applicator placed in the vaginal and uterine cavity, and/or through interstitial (IS) catheters guided through the applicator and implanted in tissue. Accurate understanding of source cable and catheter behaviour is important due to the steep dose gradient in BT of up to 12% per mm. The purpose of this study is to develop and validate comprehensible computer models to simulate: (1) BT source paths, and (2) insertion forces of catheters in curved IC/IS applicator channels. These models can aid novel (3D-printed) BT applicator development and improve source path models used for treatment planning. Method Source cables or catheters were modelled as an interconnected series of rigid beam elements connected through torsional springs. For evaluating the source cable model, simulated paths of a Flexitron source cable (Elekta, Stockholm, Sweden) in CT/MR ring applicators (Elekta, diameters: Ø26, Ø30 and Ø34 mm, angles: 45° and 60°) were compared with manufacturer-specified source paths. For validating catheter models, simulated ProGuide 6F catheter with obturator (Elekta) insertion forces in S-shaped channels with varying design parameters (curvature, geometric torsion, and clearance) were compared with force measurements in dedicated 3D-printed templates. Results and discussion Median and maximum differences between simulated and manufacturer-specified dwell positions were 0.5 – 1.2 mm and <2.0 mm respectively in all but one ring applicator. Simulated catheter insertion force results were in close agreement with experimental results for all channel design parameters. Conclusion The developed models show promising results in predicting the behaviour of flexible instruments in BT applicators. Insights from these models can aid novel applicator design with improved motion and force transmission of BT instruments, and contribute to overall treatment precision.