Author: Rohith Kaiyum, Ozzy Mermut, Alexandra Rink 👨🔬
Affiliation: Department of Medical Biophysics, University of Toronto, Department of Physics and Astronomy, York University 🌍
Purpose: To investigate the relationship between chemical features and real-time response to ionizing radiation dose of radiochromic diacetylene crystals.
Methods: A number of radiochromic diacetylene crystals were prepared by varying: (a) the stoichiometric ratio of Li+ and pentacosa-10, 12-diynoic acid (PCDA), (b) the cation used, and (c) the length of the alkyl chain on the diacetylene. The crystals were formulated in gelatin and deposited between two polyethylene sheets forming a film. All films were irradiated under standard or FLASH conditions within a custom phantom equipped with optical fibers for transmission mode spectroscopy, enabling real-time optical measurements. Crystal morphology was examined through scanning electron microscopy or light microscopy.
Results: The 0.2:1 stoichiometric ratio of Li+ to PCDA, an analogue of the commercial material in GafChromic EBT-3 films, had a unique macroscopic presentation, and water incorporated within the crystal itself. Compared to either PCDA, or 1:1 LiPCDA, this arrangement resulted in the highest apparent sensitivity, defined as change in optical density per Gy, and a shifted absorbance peak. Addition of other ions to PCDA yielded mixed results, with some crystals unresponsive to dose over the ranges tested. Due to its similarity to GAFchromic EBT-3 in terms of crystal structure and spectral peak position, the 1:1 Zn combined PCDA was further examined. The Zn samples had linear dose response up to 25Gy but with a lower apparent dose sensitivity relative to PCDA. When the alkyl chain length was shortened, a decrease in apparent sensitivity was observed. However, the decrease was non-monotonic as further shortening did not result in continued loss in sensitivity.
Conclusion: The response to ionizing radiation dose of radiochromic diacetylene crystals has a complex relationship between the diacetylene chemistry, and the water content of the diacetylene crystal. This study allows for optimization of radiochromics for a range of clinical dosimetric applications.