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  5. Multichannel Normalized Pixel Value as a Response Function for Radiochromic Film Dosimetry Enables Simultaneous Dose Response Linearization and Scanner Response Correction

Multichannel Normalized Pixel Value as a Response Function for Radiochromic Film Dosimetry Enables Simultaneous Dose Response Linearization and Scanner Response Correction

S Aldelaijan1,2,3,4,5*, P Papaconstadopoulos6 , H Bekerat4 , M Khosravi3 , M Bhagwat3,5 , J Seuntjens1 , S Devic1,4 , I Buzurovic3,5 , (1) McGill University, Montreal, QC, (2) King Faisal Specialist Hospital & Research Center, Riyadh, (3) Dana Farber/Brigham and Women's Hospital, Boston, MA, (4) Jewish General Hospital, Montreal, QC, (5) Harvard Medical School, Boston, MA, (6) Netherlands Cancer Institute, Amsterdam, Netherlands,

Presentations

(Wednesday, 7/17/2019) 7:30 AM - 9:30 AM

Room: 303

Purpose: To introduce a model that reproducibly linearizes the response from radiochromic film (RCF) dosimetry systems at extended dose range and to introduce a novel correction method for scanner response variation and inhomogeneity.

Methods: Six calibration curves were established for six different lot numbers of EBT3 GAFCHROMIC™ film model based on four EPSON scanners (10000XL (2 units), 11000XL, 12000XL) at three different centers. These films were calibrated in terms of absorbed dose to water based on TG51 protocol or TRS398 with dose ranges up to 40 Gy. The film response was defined in terms of a proposed normalized pixel value (nPV(ᴿᴳᴮ)) as a summation of first order equations based on information from red, green and blue channels. The fitting parameters of these equations are chosen in a way that makes the film response equal to dose at the time of calibration. Since the response of the RCF dosimetry system at the time of calibration usually relates to the central area of the scanning bed, a simple integrated correction factor that takes into account the difference in scanning states during calibration and measurements was introduced.

Results: Utilizing multichannel-features into the normalized pixel value response produced linear response to absorbed dose (slope of 1) in all six RCF dosimetry systems considered in this study. Integrating the multichannel correction into the response function formalism mitigated scanner response variations of as much as ±10% at lower doses and scanner bed inhomogeneity of ±8% to the level of measured uncertainty. The total dosimetric uncertainty achieved was at the level of 2.0-3.0% for systems with doses up to 40 Gy.

Conclusion: Combining response linearity with a correction for scanner response variation leads to a sustainable RCF dosimetry system that mitigates systematic shifts in response and reduces potential errors in reporting relative information from the film response.

Funding Support, Disclosures, and Conflict of Interest: S.A. is supported by the scholarship program at King Faisal Specialist Hospital & Research Centre (KFSH&RC). S.A. acknowledges partial support by the CREATE grant of the Natural Sciences and Engineering Research Council (Grant num: 432290).

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