TITLE:
Principal Component Analysis of EBT2 Radiochromic Film for Multichannel Film Dosimetry
AUTHORS:
Richard E. Wendt III
KEYWORDS:
Principal Component Analysis, Radiochromic Film, Multichannel Film Dosimetry
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.3 No.3,
August
13,
2014
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.