SU-E-T-83: Potential Improvements in Nonstandard Beam Quality Correction Factor Measurements Using Radiochromic Film Mutlichannel Analysis

Abstract

Purpose: The main goal of this study is to improve the precision and accuracy to which nonstandard beam quality correction factors (kQ) are measured using a novel method of mutlichannel analysis for radiochromic film dosimetry. Methods: A method to reduce systematic errors caused by imperfections in the process of film fabrication is proposed. For each channel of the 48‐bit RGB signal, the error in scanner signal is characterized as a function of the 3 channels using a multidimensional Taylor expansion. Bands of films irradiated with uniform dose are used to estimate the coefficients of the expansion. Achievable uncertainty levels are estimated using EBT and EBT2 film measurements. Results: The method is compared with a single‐channel method using only the red component of the signal. Using the same set of films, results show that the method diminishes uncertainty levels by a factor of 1.5 to 2 in relative dosimetry using EBT and EBT2 films. Results also show that systematic errors are significantly reduced with the method. Uncertainty levels obtained with EBT2 fall below the ones previously obtained with EBT using the red channel only. Conclusions: The method presented in this study can potentially improve the precision and accuracy to which kQ factors are currently measured in nonstandard beams. This study shows that levels of uncertainty of about 0.25% (1‐sigma) on relative dose measurements can be reached with radiochromic film. The study also shows that EBT2 film is an appropriate candidate for such measurements.