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An Improved Sensitometric Calibration Function for Radiochromic Film Dosimetry

T Ren1,2*, J Bourland1,2 , (1) Wake Forest School of Medicine, Winston-Salem, NC, (2) Wake Forest University, Winston-Salem, NC


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To develop and test a new calibration function, REN function for radiochromic film dosimetry. This new calibration function correlates the optical density values/unprocessed grayscale response from a flatbed scanner to dose values. To compare the performance of REN function to the typically used functions for dose calculations.

Methods: All the Gafchromic™ EBT3 film pieces were irradiated by a 10x10 cm² open field of 6 MV X-rays from a calibrated Elekta Versa™ HD linear accelerator. Two sets of dose values for calibration were obtained at depth 5 cm at SAD=100 cm. Doses for both sets were approximately in geometric sequence. One set has range from 0 to 4.2 Gy with the approximate common ratio of 1.2 excluding the unexposed film piece. The other set ranges from 0 to 16 Gy with the approximate common ratio of 2 excluding the unexposed film piece. The two calibration scans were performed on an Epson Expression 10000XL photo scanner. A thin glass sheet was used to compress film pieces during the scanning process to avoid any Callier effect. The performance of the new calibration function was compared to the typically used functions, rational function (first order for both numerator and denominator) and third order polynomials. Root mean square error (RMSE), sum of squares error (SSE) and R-square were used to evaluate the fit goodness of the functions.

Results: For both sets of dose values, REN function provides the better fitting results with lower RMSE and SSE for all the color channels than the polynomials and rational functions. The film measurement of an IMRT QA plan was calculated using REN function. The pass (γ≤1) rate of gamma index analysis was 99.80%(mean gamma value 0.21) with 3%/3mm tolerance.

Conclusion: The new function, REN function is suitable for Gafchromicâ„¢ EBT3 film sensitometric calibration with high dynamic range.


Radiochromic Film, Densitometry, Dose


TH- Radiation dose measurement devices: Radiochromic film

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