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Protoacoustic range verification by direct comparison with beam range measurements using a tissue-equivalent polymer
Takeshi Miyashita1, Ye Chen1, Yasutoshi Kuriyama2
1Faculty of Engineering, Hokkaido University, Sapporo, Japan.
Summary
Polymer gel dosimeters directly measure proton beam range, validating protoacoustic measurements in proton therapy. This method avoids uncertainties associated with Monte Carlo simulations for improved accuracy.
Area of Science:
- Medical physics
- Radiation oncology
- Biomedical engineering
Background:
- Protoacoustics shows promise for in vivo range verification in proton therapy.
- Conventional tissue-mimicking phantoms (TMPs) rely on Monte Carlo (MC) simulations for ground truth, which can introduce errors.
- Uncertainties in MC simulations stem from material properties and dose model inaccuracies.
Purpose of the Study:
- To propose and evaluate a novel TMP for concurrent dose distribution and protoacoustic measurements.
- To eliminate the need for MC simulations in protoacoustic range verification.
- To improve the accuracy of in vivo range verification in proton therapy.
Main Methods:
- Utilized normoxic N-vinylpyrrolidone-based polymer gel dosimeters as TMPs.
- Irradiated gels with a 226.5 MeV proton beam and analyzed using magnetic resonance imaging.
- Measured protoacoustic ranges with an optical hydrophone (time-of-arrival and simulation-based methods).
Main Results:
- Gel dosimeter and protoacoustic range differences were within 1 mm for both gel sizes.
- Protoacoustic ranges showed a maximum deviation of 2.1 mm compared to MC simulations.
- Discrepancies with MC simulations may be due to inaccuracies in assumed material properties.
Conclusions:
- Polymer gel dosimeters offer a direct validation method for protoacoustic range measurements.
- This approach circumvents the uncertainties inherent in MC simulations.
- Enables more reliable in vivo range verification in clinical proton beams.
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