Evaluation of scanner image properties of radiochromic film for measuring effective energy

Abstract

The effective energy calculated using the halfvalue layer (HVL) is an important parameter for quality assurance (QA) and quality control (QC). However constant monitoring has not been performed because measurements using an ionization chamber (IC) are time-consuming and complicated. To solve these problems, a method using radiochromic film (GAFCHROMIC EBT2 dosimetry film (GAFEBT2) with slight energy dependency errors), a flatbed scanner and step-shaped aluminum filters has been developed. In this study, a mobile scanner was used for digital image acquisition of GAF-EBT2, because the mobile scanner has characteristics of low cost and increased portability compared with a flatbed scanner. GAF-EBT2 was scanned using the flatbed scanner in transmission mode and reflection mode, and the mobile scanner in reflection mode. The HVL (X-ray tube voltages of 120 kVp) was evaluated using the density attenuation ratio. The effective energies obtained using HVL of GAFEBT2 (flatbed scanner, mobile scanner) and an IC dosimeter were compared. In reflection mode, both the flatbed scanner and the mobile scanner provided a flat density profile curve without the error of the light source. The difference ratios of the effective energies by each method using a flatbed scanner (reflection mode) and a mobile scanner (reflection mode) with GAF-EBT2 were less than 5 % compared with results of an IC dosimeter. It is considered that this method offers a simple means of determining HVL for QA and QC consistently and quickly without the need for an IC dosimeter.