Towards high spatial resolution tissue-equivalent dosimetry for microbeam radiation therapy using organic
Jessie A Posar1, Matthew Large1, Saree Alnaghy1
1Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia.
Journal of Synchrotron Radiation
|September 3, 2021
Summary
This study explores organic semiconductors as tissue-equivalent dosimeters for microbeam radiation therapy (MRT). The developed dosimeter shows promise for high spatial resolution and cost-effectiveness in synchrotron radiation fields.
Area of Science:
- Medical Physics
- Materials Science
- Radiation Dosimetry
Background:
- Microbeam radiation therapy (MRT) utilizes spatially fractionated ultra-high-dose-rate beams to enhance differential responses between normal and tumor tissues.
- Effective quality assurance for MRT necessitates a dosimeter with tissue equivalence, high radiation tolerance, and superior spatial resolution, a challenge yet to be fully addressed.
Purpose of the Study:
- To investigate the feasibility of using a thin-film organic semiconductor as a tissue-equivalent dosimeter for microbeam radiation therapy (MRT) applications.
- To evaluate the dosimeter's performance, including its response, stability, spatial resolution, and dose-rate dependence under synchrotron radiation conditions.
Main Methods:
- A 500 nm thick organic semiconductor device was irradiated using three different beam filters (48, 76, 88 keV) at the Australian Synchrotron's Imaging and Medical Beamline.
- The device's response, calibration factor, and percentage depth dose (PDD) were measured and compared with a PTW microDiamond detector.
- Geant4 simulations were employed to understand the origin of additional dose peaks and their dependence on X-ray energy spectra.
Main Results:
- The organic semiconductor dosimeter demonstrated stabilized response (30% efficiency) after 30 kGy irradiation, with minimal variation (0.5%) at higher doses.
- A consistent calibration factor of 1.02 ± 0.005 µGy/count was achieved across all tested X-ray energy spectra, highlighting its tissue equivalence.
- The dosimeter accurately reconstructed microbeam profiles, although dose-rate dependence and optical photon effects influenced peak detection, as confirmed by simulations.
Conclusions:
- Organic photodetectors show significant potential as cost-effective, flexible, and tissue-equivalent dosimeters for MRT, offering high spatial resolution.
- Optimizing material packaging through solution processing and employing non-fluorescent barrier films can mitigate observed limitations.
- Further development could lead to advanced dosimetry solutions for synchrotron radiation applications.
