Optimum wavelength of ultraviolet rays in gafchromic EBT2

Abstract

Introduction Gafchromic films have been used for the measurement of X-ray dose in diagnostic radiology. UV-A ray can be used as a substitute for X-rays in the double exposure technique to compensate for nonuniformity error of Gafchromic EBT2. Purpose When using a UV-A light emitting diode (UV-A LED), it is necessary to determine the optimal UV-A wavelength to react with the active layer of Gafchromic EBT2. Therefore, changes in the optical density of Gafchromic EBT2 induced by UV-A were investigated by irradiating it at various wavelengths with UV-A LED. Materials and methods At first, Gafchromic EBT2 was pre-irradiated using a uniform UV-A by using fluorescent lamp for 60 min from a distance of 72 cm to reduce nonuniformity error. Second, Gafchromic EBT2 was irradiated for 60 min from a distance of 5.3 cm using a UV-A LED at a wavelength of 353–410 nm. The maximum, minimum, and mean ± standard deviation of pixel values of the subtraction images were evaluated using 0.5 inch of circular region of interest (ROI). The most sensitive wavelength of UV ray was decided. In addition, UV strength was measured in each UV-A LED. Results When a UV-A LED wavelength of 375 nm was used, the mean ± SD of pixel value of Gafchromic EBT2 was indicated highly pixel value. It was 8915.25 ± 608.86. A 375 nm wavelength UV-A was most effective and sensitive for Gafchromic EBT2. Conclusion The 375 nm wavelength of UV-A is available as a substitute for X-rays in the double exposure technique. Disclosure Research supported by JSPS KAKENHI Grant Number 26460740 .