Suitability of radiochromic films for dosimetry of low energy X-rays

This study examined the response characteristics of three commercially available radiochromic films when exposed to low energy (50 kVp) X-rays. The aim was to evaluate the films for potential use in 2D dosimetry for a low-kV intraoperative radiotherapy (IORT) device known as the 'Intrabeam'. Dose-response relationships were obtained for Gafchromic EBT, XR-RV2, and XR-QA film in water at several distances from the Intrabeam device. It was found that the dose rates from the source were excessive for use of the XR-QA film, and that all three film types showed significant energy dependence within the limits of measurement uncertainty. Basic modeling of primary X-ray spectra indicated large changes in the lower energy components with distance from the source, and it is hypothesized that the changes in film response are a result of changes in film energy response. This is in contrast to previous studies indicating less or negligible energy response. All films showed non-linearity in response over the ranges examined. These results imply significant limitations for the use of these films for low-kV dosimetry.