Program Information
Real-Time In Vivo Dosimeters Using LiPCDA and Optical Fibers
A Rink1*, A Croteau2 , S Caron2 , O Mermut2 , DA Jaffray1 , (1) Princess Margaret Cancer Center, Toronto, ON, (2) National Optics Institute, Quebec, Quebec
Presentations
SU-E-T-672 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To investigate dosimeter prototypes made with lithium pentacosa-10,12-diynoate (LiPCDA, the material used in GafChromic EBT films) and optical fibers for their suitability in real-time in vivo measurements.
Methods: The prototypes, made with 500 μm plastic optical fibers and 8.5 μm thickness of LiPCDA at fiber tip, were irradiated with a 6 MV beam. To investigate the efficacy of pre-irradiation calibration, the probes were irradiated to 2 Gy twice, with 5 minutes in between. Net optical density values (netOD) around the main absorbance peak were compared, and effect of correcting second measurement by the first was assessed. Ageing was assessed by irradiating two prototypes to 2 Gy and comparing the netOD to that obtained for 15 prototypes from the same batch 12-14 months earlier. To measure angular dependence, the probes were pre-irradiated with beam perpendicular to fiber axis and then, 5 minutes later either perpendicular or parallel to fiber axes. The thickness-corrected netOD measurements were compared.
Results: Standard deviation of netOD for probes of the same batch was measured to be 5-6%. When netOD was corrected for material thickness by using results from the first irradiation, the standard deviation decreased to 1.3%. This was comparable to the uncertainty in measurements observed with a single probe and is attributed to variations in light output, spectrometer noise and splitter-to-probe connection variations. Comparison of netOD values obtained a year apart failed to illustrate statistically significant decrease in sensitivity due to ageing (0.38 ± 0.03 and 0.3656 ± 0.0003). NetOD measured with MV beam parallel to fiber was within error of netOD measured with MV beam perpendicular to fiber.
Conclusion: Current prototype construction allows for shelf life of at least one year. With material thickness corrected for, the prototypes can measure dose with an uncertainty below 2% at a given energy and dose rate.
Funding Support, Disclosures, and Conflict of Interest: This work has been funded by the Ontario Centres of Excellence Market Readiness grant. The authors have no conflict of interest to declare.
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