Influence of scattered radiation on Gafchromic EBT3

Abstract

Gafchromic EBT3 (EBT3) is used as a radiochromic film in half-value layer (HVL) measurement methods, which are used to calculate the effective energy for QA and QC. HVL measurements using EBT3 display a precision of less than 5 % compared with the results of standard method with an ionization chamber (IC) dosimeter, and offer a simple procedure for determining the HVL consistently and quickly without the need for an IC. However, it is difficult to apply this technique because of the scattered radiation caused by the geometric layout of the X-ray computed tomography (CT) apparatus. In this study, the effect of scattered radiation on EBT3 is investigated. It was found that the EBT3 is not affected by scattered radiation at positions beyond 50 mm from the scattering substance. Therefore, the results suggest that EBT3 is suitable for use in X-ray CT HVL measurements. On the other hand, when the distance from the scattering substance was 10 mm or less, EBT3 showed very high absorption compared to a semiconductor detector. Therefore, EBT3 is more sensitive than the semiconductor detector at a close range and can be used to measure scattered radiation when the distance from the scattering substance is 10 mm or less.