Two-dimensional modeling for the non uniform response of scanner-radiochromic film systems
Keywords:
Dosimetry, radiochromic films, scanner, nonuniformity, verificationAbstract
Radiochromic films are increasingly used as a verification method for radiotherapy treatments. This work aims at characterizing and correcting the non-uniformity artifacts introduced by the scanner-radiochromic film system. We have found signs of an appreciable pattern not only at the lateral dimension but also along the other dimension. To study this, the dose distribution per monitor unit (MU) on a plane at a reference depth is measured by an ionization chamber array PTW 729. Corresponding distributions for different doses are measured with radiochromic films (EBT3) from distinct batches, whose reading is performed by using two scanners EPSON EXPRESSION 10000XL. By fitting 2D polynomial functions to the resulting images, we model the bidimensional behavior of scanner-radiochromic film system. Therefore, a family of surfaces for each color channel and for a range of considered doses, equivalently optical density (OD), is employed to correct the artifacts. A consistent two-dimensional pattern has been found for both scanners and all the studied ODs. On the film corner areas, both effects may join thus the combined correction becomes necessary. Consequently, a new two-dimensional correction method is proposed and built together with an in-house software for a quick setup in any institution.
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