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
Highlights
450 Katsuda et al.: Three UV exposures of Gafchromic film of active layer thicknesses can affect the measured doses
The UV peak wavelengths of nm (UV-A), UV-B, and UV-C were used to irradiate the front side of Gafchromic EBT2
We considered that UV-A or UV-B could be used to effectively irradiate Gafchromic EBT2 and EBT3
Summary
450 Katsuda et al.: Three UV exposures of Gafchromic film of active layer thicknesses can affect the measured doses. In the diagnostic range for X-rays, exposure can be slightly changed based on Gafchromic film density. Signal data for X-ray exposures are affected by these nonuniformity errors. A double-exposure technique is used to reduce these nonuniformity errors.[3] it is difficult to provide homogenous X-ray exposure over a wide area, such as a 14 × 17 inch format. Gafchromic films, UV irradiation was originally considered to be taboo because it introduces density noise for X-ray measurements.[6] Nonuniformity errors are expressed using UV irradiation as a substitute for X-rays in a double-exposure technique. UV light can be uniformly irradiated over a wide area, and nonuniformity errors can be reduced by a subtraction method. We performed UV (360 nm) exposure (0.018 mW / cm2) as a doubleexposure technique for Gafchromic EBT and obtained good results.[7]
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