  The purpose of this study was to find the most accurate model for
radiochromic film dosimetry by comparing different channel independent
perturbation models. A model selection approach based on (algorithmic)
information theory was followed, and the results were validated using
gamma-index analysis on a set of benchmark test cases. Several questions were
addressed: (a) whether incorporating the information of the non-irradiated
film, by scanning prior to irradiation, improves the results; (b) whether
lateral corrections are necessary when using multichannel models; (c) whether
multichannel dosimetry produces better results than single-channel dosimetry;
(d) which multichannel perturbation model provides more accurate film doses. It
was found that scanning prior to irradiation and applying lateral corrections
improved the accuracy of the results. For some perturbation models, increasing
the number of color channels did not result in more accurate film doses.
Employing Truncated Normal perturbations was found to provide better results
than using Micke-Mayer perturbation models.} Among the models being compared,
the triple-channel model with Truncated Normal perturbations, net optical
density as the response and subject to the application of lateral corrections
was found to be the most accurate model. The scope of this study was
circumscribed by the limits under which the models were tested. In this study,
the films were irradiated with megavoltage radiotherapy beams, with doses from
about 20 cGy to 600 cGy, entire (8 ${\rm inch}$ $\times$ 10 ${\rm inch}$) films
were scanned, the functional form of the sensitometric curves was a polynomial
and the different lots were calibrated using the plane-based method.
