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Enhancing dose conformity in head and neck intensity-modulated proton therapy using a novel dynamic multi-leaf
Yushi Wakisaka1,2, Yuki Tominaga1,2, Yuya Miyasaka3
1Department of Radiotherapy, Medical Co. Hakuhokai, Osaka Proton Therapy Clinic, Osaka, Japan.
Medical Physics
|February 19, 2026
Summary
Integrating dynamic multi-leaf collimators (dMLC) with intensity-modulated proton therapy (IMPT) significantly spares organs at risk in head and neck cancer patients. This advanced technique improves dose reduction to surrounding tissues while maintaining target coverage and plan robustness.
Area of Science:
- Radiation Oncology
- Medical Physics
- Cancer Treatment
Background:
- Proton pencil beam scanning (PBS) offers conformal dose distributions but faces challenges with penumbra degradation due to range shifters and air gaps.
- Penumbra degradation in head and neck PBS can increase organ at risk (OAR) doses or compromise target coverage.
- Dynamic multi-leaf collimators (dMLC) enhance dose conformity in single-field uniform dose (SFUD) delivery, and intensity-modulated proton therapy (IMPT) allows for greater flexibility in their use.
Purpose of the Study:
- To integrate dMLC into IMPT for head and neck cancer treatment.
- To propose and evaluate a novel dMLC leaf positioning strategy within IMPT.
- To assess the dosimetric impact, target coverage, and OAR sparing benefits of this integrated approach.
Main Methods:
- Retrospective treatment planning for five head and neck cancer patients using IMPT with three beam angles.
- Comparison of three techniques: uncollimated PBS, dMLC covering the target (dMLCcover), and dMLC blocking OARs (dMLCblock).
- Evaluation of dose-volume histogram (DVH) metrics under various setup and range uncertainties, with dose calculation accuracy validated using 2D gamma analysis.
Main Results:
- dMLC integration with IMPT significantly reduced OAR doses while maintaining target coverage and robustness compared to uncollimated PBS.
- The dMLCblock technique showed superior dose sparing for OARs, especially those adjacent to the target.
- dMLCcover provided the greatest reduction in mean doses to eyeballs/optic nerves and D2% to the optic chiasm, brain, and brainstem, with validated dose calculation accuracy (>95% gamma passing rate).
Conclusions:
- The combination of IMPT and dMLC offers significant dosimetric advantages for head and neck cancer treatment.
- This approach shows promise for clinical application, potentially improving OAR sparing and treatment efficacy.
- Further research is needed to validate efficacy and safety across diverse cases, focusing on leaf positioning accuracy and biological effectiveness.
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