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Optical Calibration of Radiochromic Film Thickness With IR Dye

R Kaiyum1*, N Allam2, C Schruder1, O Mermut1, A Rink1,3, (1) Department of Physics and Astronamy, York Univeristy, Toronto, ON, CA, (2) Department Of Medical Biophysics, University Of Toronto, ON , CA, (3) The Princess Margaret Cancer Centre, University Health Network, Toronto, ON, CA

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To optically calibrate for variations in lithium pentacosa-10,12-diynoate (LiPCDA) radiochromic film thickness, for use in real-time fiber optic dosimetry, through the incorporation of an infrared dye.


Methods: Four infrared (IR) dyes, with absorbance peaks occurring at 783 nm, 806 nm, 868 nm and 880 nm, were selected for study. Solubility tests were performed with all four dyes in distilled water to ensure IR dye can remain suspended in aqueous solution. Dilutions were made to determine the concentration required to yield an absorbance value of at least 0.5 in the final film coating. The dyes were then incorporated into the aqueous LiPCDA solutions and coated onto Mylar. The Mylar coatings were irradiated using 254 nm UV photons and scanned (400 nm to 1000 nm) on a spectrophotometer to ensure that the integrated IR dye and LiPCDA peaks can be spectrally resolved and that the dye was stable with absorbed dose.


Results: The two dyes in the higher IR (868 nm, 880 nm) region were eliminated as candidates since they were not water-soluble. IR dye 783 nm and 806 nm were water-soluble at low concentrations and remained suspended in solution. For both dyes, less than 0.005% of total mass resulted in absorbance >0.5 at the main peak in solution. Preliminary data suggests that <0.5% of total mass of IR 806 yielded 0.5 absorbance in a film coating, but potentially aggregated interfering with the main 635 nm absorbance peak of LiPCDA. IR 783 was observed to shift in absorbance wavelength once incorporated into the radiochromic film coating. The location and absorbance was otherwise stable with increased irradiation (254 nm UV light).


Conclusion: IR 783 is a suitable dye for thickness calibration in a radiochromic film using LiPCDA with 635 nm radiation-induced absorbance band. Long-term stability testing is needed to confirm this result.

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Funding Support, Disclosures, and Conflict of Interest: Funding provided by the Canadian Institutes of Health Research Project Grant PJT-162294

Keywords

Radiochromic Film, Dosimetry, Calibration

Taxonomy

Not Applicable / None Entered.

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