Comparing three UV wavelengths for pre‐exposing Gafchromic EBT2 and EBT3 films

Abstract

Gafchromic films are used for X‐ray dose measurements during diagnostic examinations and have begun to be used for three‐dimensional X‐ray dose measurements using the high‐resolution characteristics of Gafchromic films for computed tomography. However, the problem of unevenness in Gafchromic film active layers needs to be resolved. Double exposures using X‐rays are performed during therapeutic radiology, although this is difficult for a diagnostic examination because of a heel effect. Thus, it has been suggested that ultraviolet (UV) radiation be used as a substitute for X‐rays. However, the appropriate UV wavelength has not been determined. Thus, we conducted this study to decide an appropriate UV wavelength. UV peak wavelengths of 245 nm (UV‐A), 310 nm (UV‐B), and 365 nm (UV‐C) were used to irradiate EBT2 and EBT3 films. Each UV wavelength was irradiated for 5, 15, 30, and 60 min, and irradiation was then repeated every 60 min up to 360 min. Gafchromic films were scanned after every irradiation using a flatbed scanner. Images were split into RGB images, and red images were analyzed using ImageJ, version 1.44, image analysis software. A region of interest (ROI) one‐half inch in diameter was placed in the center of subtracted Gafchromic film images, and UV irradiation times were plotted against mean pixel values. There were reactions in the front and back of Gafchromic EBT3 and the back of Gafchromic EBT2 with UV‐A and UV‐B. However, UV‐C resulted in some reactions in both sides of Gafchromic EBT2 and EBT3. The UV‐A and UV‐B wavelengths should be used.PACS number(s): 87.53 Bn

Intensities of incident and transmitted ultraviolet-a rays through gafchromic films

“…The Gafchromic EBT3 film without a UV protection layer was considered suitable for this study. [ 9 ] Moreover, the active layer (lithium pentacos-10, 12-diynate) of Gafchromic EBT3 can be considered representative of other Gafchromic films. [ 7 ]…”

“…[ 7 ] UV-A rays emitted from a fluorescent lamp (peak wavelength 365 nm) react more effectively with Gafchromic EBT2 and EBT3 than do UV-B and UV-C (peak wavelength 320 nm and 245 nm[ 8 ]) rays. [ 9 10 ]…”

Development of a three‐dimensional dose evaluation method for computed tomography

“…9 , 10 The density of the active layer increases with the amount of exposure to X‐rays and ultraviolet rays. 11 , 12 Compared with that of the 10‐cm‐IC, the spatial resolution of radiochromic films is exceedingly high and thus measuring doses in local regions using radiochromic films is more convenient. However, as the density change is expressed using a pixel value and may differ for each batch of films, a calibration curve to convert the pixel values into doses must be created.…”

“…Gafchromic films are self‐developing dosimetry films that do not require processing or chemicals and can be handled under ambient room light 9,10 . The density of the active layer increases with the amount of exposure to X‐rays and ultraviolet rays 11,12 . Compared with that of the 10‐cm‐IC, the spatial resolution of radiochromic films is exceedingly high and thus measuring doses in local regions using radiochromic films is more convenient.…”