Principal Component Analysis of EBT2 Radiochromic Film for Multichannel Film Dosimetry

Richard E. Wendt III

Department of Imaging Physics, The University of Texas M. D. Anderson Cancer Center, Houston, USA.

DOI: 10.4236/ijmpcero.2014.33021                

Abstract

Radiochromic film with a dye incorporated into the radiation sensitive layer [Gafchromic EBT2, Ashland, Inc.] may be digitized by a color transparency scanner, digitally processed, and calibrated so that a digital image in units of radiation absorbed dose is obtained. A transformation from raw scanner values to dose values was developed based upon a principal component analysis of the optical densities of the red, green and blue channels of the color image of a dose of 0.942 Gy delivered by a Sr-90/Y-90 disk-shaped source. In the order of increasing eigenvalue, the three eigenimages of the principal component analysis contained, by visual inspection, 1) mainly noise; 2) mainly a pattern of irregular streaks; and 3) most of the expected dose information along with some of the same background streaking that predominated in the second eigenimage. The combination of the second and third eigenimages that minimized the background streaking was converted into a transformation of the red, green and blue channels’ optical densities and applied to films with a range of doses from 0 to 63.7 Gy. The curve of dose vs. processed optical density was fit by a two-phase association curve. This processing was applied to a film exposed from its edge by a different Y-90 source in a configuration that was modeled by Monte Carlo simulation. The depth-dose curves of the measurement and simulation agree closely, suggesting that this approach is a valid method of processing EBT2 radiochromic film into maps of radiation absorbed dose.

Keywords

Principal Component Analysis, Radiochromic Film, Multichannel Film Dosimetry

Conflicts of Interest

The authors declare no conflicts of interest.

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