Multibody dynamic modeling of the behavior of flexible instruments used in cervical cancer brachytherapy

Robin Straathof*, Jaap P. Meijaard, Sharline M. van Vliet-Pérez, Inger Karine K. Kolkman-Deurloo, Remi A. Nout, Ben J.M. Heijmen, Linda S.G.L. Wauben, Jenny Dankelman, Nick J. van de Berg

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

1 Citation (Scopus)
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Background: The steep radiation dose gradients in cervical cancer brachytherapy (BT) necessitate a thorough understanding of the behavior of afterloader source cables or needles in the curved channels of (patient-tailored) applicators. Purpose: The purpose of this study is to develop and validate computer models to simulate: (1) BT source positions, and (2) insertion forces of needles in curved applicator channels. The methodology presented can be used to improve the knowledge of instrument behavior in current applicators and aid the development of novel (3D-printed) BT applicators. Methods: For the computer models, BT instruments were discretized in finite elements. Simulations were performed in SPACAR by formulating nodal contact force and motion input models and specifying the instruments’ kinematic and dynamic properties. To evaluate the source cable model, simulated source paths in ring applicators were compared with manufacturer-measured source paths. The impact of discrepancies on the dosimetry was estimated for standard plans. To validate needle models, simulated needle insertion forces in curved channels with varying curvature, torsion, and clearance, were compared with force measurements in dedicated 3D-printed templates. Results: Comparison of simulated with manufacturer-measured source positions showed 0.5–1.2 mm median and <2.0 mm maximum differences, in all but one applicator geometry. The resulting maximum relative dose differences at the lateral surface and at 5 mm depth were 5.5% and 4.7%, respectively. Simulated insertion forces for BT needles in curved channels accurately resembled the forces experimentally obtained by including experimental uncertainties in the simulation. Conclusion: The models developed can accurately predict source positions and insertion forces in BT applicators. Insights from these models can aid novel applicator design with improved motion and force transmission of BT instruments, and contribute to the estimation of overall treatment precision. The methodology presented can be extended to study other applicator geometries, flexible instruments, and afterloading systems.

Original languageEnglish
Pages (from-to)3698-3710
Number of pages13
JournalMedical Physics
Issue number5
Publication statusPublished - 2024


We would like to acknowledge the contributions of Yury Niatsetski and Dr. Teunis van Manen (Elekta Brachytherapy, Veenendaal, the Netherlands) for their help with the source path simulations. The authors are grateful to Eva Hofland (Oceanz, Ede, the Netherlands) for providing the 3D‐printed templates. This project was supported by a grant from the Dutch Research Council (NWO), Dutch Cancer Society (KWF), and Top Sector Life Sciences & Health (LSH) (Project No. 17921).

Remi Nout has received research grants from the Dutch Research Council (NWO), Dutch Cancer Society (KWF), Elekta, Varian, and Accuray. The remaining authors have no relevant conflicts of interest to disclose.


  • cervical cancer brachytherapy
  • finite element modeling of source motion
  • flexible instrument
  • multibody dynamics


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