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Design of static and dynamic ridge filters for FLASH-IMPT: A simulation study
Guoliang Zhang1, Wenchao Gao2, Hao Peng1,3
1Department of Medical Physics, School of Physics and Technology, Wuhan University, Wuhan, China.
Medical Physics
|May 20, 2022
Summary
New ridge filters for intensity-modulated proton therapy (IMPT) eliminate layer switching, significantly reducing treatment time for FLASH applications. These filters maintain dose conformity while enabling high dose rates, proving promising for advanced cancer treatments.
Area of Science:
- Medical Physics
- Radiation Oncology
- Biophysics
Background:
- Intensity-modulated proton therapy (IMPT) is an advanced radiation therapy technique.
- Current IMPT methods, like pencil beam scanning (PBS), often require energy or layer switching, increasing treatment time.
- FLASH radiotherapy aims to deliver radiation doses at ultra-high dose rates to potentially reduce side effects.
Purpose of the Study:
- To design and optimize ridge filters for IMPT, specifically for FLASH applications.
- To evaluate if ridge filters can eliminate the need for layer switching in IMPT.
- To assess the potential of ridge filter-based IMPT for reducing total treatment time and achieving high dose rates.
Main Methods:
- Generated unique dose-influence matrices by passing proton beams through varying thicknesses of material.
- Created conventional IMPT plans using a nonlinear solver to establish reference dose distributions.
- Optimized ridge filter designs (static model A, dynamic model B) using reference plan spot weights.
- Verified ridge filter designs via GEANT4 simulations in a water phantom and a head and neck (H&N) cancer case.
Main Results:
- Both static and dynamic ridge filter models achieved high dose conformity, comparable to reference IMPT plans.
- Achieving a dose rate of 40 Gy/s over 90% of the planning target volume (PTV) required a beam intensity of 2.5 × 10^11 protons/s for both models.
- Total treatment time was reduced by a factor of 4.9 (model A) and 6.5 (model B) compared to reference plans for a 10 Gy fraction dose.
Conclusions:
- The proposed static and dynamic ridge filter designs are effective for PBS-IMPT without layer switching.
- These ridge filters are promising for FLASH-IMPT, enabling reduced treatment times and high dose rates.
- The designs successfully maintain dose conformity, a critical factor in effective radiation therapy.
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