Dose–response linearization in radiochromic film dosimetry based on multichannel normalized pixel value with an integrated spectral correction for scanner response variations

Abstract

Purpose: To introduce a model that reproducibly linearizes the response from radiochromic film (RCF) dosimetry systems at extended dose range. To introduce a correction method, generated from the same scanned images, which corrects for scanner temporal response variation and scanner bed inhomogeneity. Methods: Six calibration curves were established for different lot numbers of EBT3 GAFCHRO-MIC TM 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. An integrated set of correction factors (one per color channel) was also introduced. These factors account for the spatial and temporal changes in scanning states during calibration and measurements. The combination of nPV RGB and this "fingerprint" correction formed the basis of this new protocol and it was tested against net optical density (netOD X¼R;G;B ) single-channel dosimetry in terms of accuracy, precision, scanner response variability, scanner bed inhomogeneity, noise, and long-term stability. Results: Incorporating multichannel features (RGB) into the normalized pixel value produced linear response to absorbed dose (slope of 1) in all six RCF dosimetry systems considered in this study. The "fingerprint" correction factors of each of these six systems displayed unique patterns at the time of calibration. The application of nPV RGB to all of these six systems could achieve a level of accuracy of AE 2.0% in the dose range of interest within modeled uncertainty level of 2.0%-3.0% depending on the dose level. Consistent positioning of control and measurement film pieces and integrating the multichannel correction into the response function formalism mitigated possible scanner response variations of as much as AE 10% at lower doses and scanner bed inhomogeneity of AE 8% to the established level of uncertainty at the time of calibration. The system was also able to maintain the same level of accuracy after 3 and 6 months post calibration.Conclusions: Combining response linearity with the integrated correction for scanner response variation lead to a sustainable and practical RCF dosimetry system that mitigated systematic response shifts and it has the potential to reduce errors in reporting relative information from the film response.

A two‐layer cylinder phantom developed for film‐based isocenter verification of radiotherapy machine

“…These scanned images were saved as tagged image file format (TIFF). The green color channel of the scanned image, which had an optimal overall response at a dose of 6–40 Gy, was used for analysis 19,20 . In addition, the scanned images may be rotated and cropped to minimize improper shifts introduced during film scanning.…”

“…The film scanning process may introduce certain errors due to influence factors such as improper placement of film, cleanliness of the scanner, and incorrect scanner settings 19 . Among them, the effects of scanning resolution and inter‐operator variation are most concerned.…”

Positional and angular tracking of HDR 192Ir source for brachytherapy quality assurance using radiochromic film dosimetry

“…Radiochromic film dosimetry system: The RCF dosimetry system consisted of: (a) EBT3 GAFCHROMIC TM film model lot# 06181801 (Ashland Inc, Wayne, NJ), (b) EPSON scanner model 12000XL (Epson, Nagano, Japan), and (c) the dosimetry protocol developed in our previous work 36 including film handling procedures, calibration, scanning instructions, image analysis, dose, and uncertainty calculation models. The film was calibrated in a 6 MV beam instead of calibrating it at HDR 192 Ir beam quality directly to a maximum dose of 40 Gy.…”

High spatial resolution dosimetry with uncertainty analysis using Raman micro‐spectroscopy readout of radiochromic films

“…RCFs have been used for two‐dimensional radiation dosimetry over the last couple of decades 12,13 . Owing to their tissue‐equivalence, energy‐independent response and high spatial resolution, RCFs are widely used for radiotherapy treatment verification and quality assurance 14,15 . RCFs contain an active layer of diacetylene monomers that polymerizes to form polydiacetylene (PDA) in response to incident ionizing radiation 16 .…”

“…12,13 Owing to their tissue-equivalence, energyindependent response and high spatial resolution, RCFs are widely used for radiotherapy treatment verification and quality assurance. 14,15 RCFs contain an active layer of diacetylene monomers that polymerizes to form polydiacetylene (PDA) in response to incident ionizing radiation. 16 The resulting change in the optical density is typically read out using transmitted or reflected visible light.…”