Monte Carlo simulations of different CT X-ray energy spectra within CTDI phantom and the influence of its changes on radiochromic film measurements.

Purpose: In this work we use Monte Carlo simulations to investigate change in Computed tomography (CT) X-ray energy spectra between exposures in air and within CT dose index (CTDI) phantom. While the results of these simulations will be relevant when measuring CTDI with any dosimeter, we apply the appropriate beam quality change correction for CTDI measurements using XR-QA2 model GafChromic™ film.

Methods: Dose profiles were measured with film strips, sandwiched between acrylic rods cut in half, placed within CTDI phantoms and scanned before and after irradiation with document scanner in reflective mode.