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Linearization of Dose Response Curve for the Radiochromic Film Dosimetry System

D Lewis

D Lewis1*, S Devic2, N Tomic2, S Aldelaijan3, F DeBlois2, M Chan4, J Seuntjens5, (1) Ashland Specialty Ingredients , Wayne, NJ, (2) McGill University, Jewish General Hospital, Montreal, Quebec, Canada (3) Saudi Food and Drug Authority, Riyadh, KSA, (4) Memorial Sloan-Kettering Cancer Center, Basking Ridge, NJ, (5) Medical Physocs Unit, McGill University, Montreal, QC, Canada

TH-E-BRB-2 Thursday 1:00:00 PM - 2:50:00 PM Room: Ballroom B

Purpose: In order to measure relative dose distribution with radiochromic film, one need to first measure an absolute dose (following previously established reference dosimetry protocol) and then convert measured absolute dose into relative dose. We present here result of our efforts to establish a functional form that converts the inherently non-linear dose response curve of the radiochromic film dosimetry system into liner one. Methods: In order to test the invariance of the proposed functional form with respect to the film or scanner model used, we have tested it on film pieces from three different GAFCHROMICTM film models (EBT, EBT-2, and EBT-3) irradiated to various doses and scanned on a single scanner. For one of the film models we have also tested it by scanning with three different flatbed scanner models (Epson V700, 1680, and 10000XL). To test our hypothesis that the proposed functional argument linearizes the response of the radiochromic film dosimetry system, we performed a measurement of percent depth dose (PDD) curves in Cobalt-60 beam. Results: Obtained R2 values indicate that the choice of the functional form of the new argument (ζ) appropriately linearizes the dose response of the radiochromic film dosimetry system we used. The linear behavior was insensitive to both film model and flatbed scanner model used. Measured PDD values using the green channel response of the GAFCHROMICTM EBT-3 film model are well within ±2% window of the local relative dose value when compared to the tabulated Cobalt-60 data. Conclusions: We demonstrate the use of a unique functional argument to linearize the inherently non-linear response of a radiochromic film based reference dosimetry system. In this way, relative dosimetry can be conveniently performed using radiochromic film dosimetry system without the need of establishing an absolute calibration curve.

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