Nobuyoshi Tanki, Sachiko Goto, Toshizo Katsuda, Rumi Gotanda, Tatsuhiro Gotanda, Tadao Kuwano
Purpose: Radiochromic film is used for quality assurance and quality control of X-ray equipment in the diagnostic radiology. In addition, three-dimensional dose distribution of computed tomography (CT) is measured. To correct the nonuniformity and uncertainty of radiochromic films for dose measurement of CT, the films are preirradiated ultraviolet (UV)-A rays. There is a difference in the UV protection strength of radiochromic films. A concern exists about the effects of the UV-A irradiation intensity. We thus irradiated with UV-A rays from the backsides of the films to assess if backside irradiation was possible.
Materials and Methods: Gafchromic XR-QA2 and RTQA2 were used in this study. The UV-A rays were simultaneously irradiated on the front and backsides of each film for 12 h. The yellow layer of each film was scanned and imaged. The average pixel values �� standard deviations (SDs) were compared. In the statistical analysis, a paired t-test was performed. To compare, the active-layer densities engendered by the UV-A rays. Calibration curve was created with 48 h of preirradiation of UV-A.
Results: The mean pixel values �� SD for Gafchromic XR-QA2 on the front and backsides were 130.776 �� 0.812 and 81.015 �� 1.128, respectively. On the other hand, the mean pixel values �� SD for Gafchromic RTQA2 on the front and backsides were 62.299 �� 1.077 and 133.761 �� 1.365, respectively. The statistical results of the paired t-test were significantly different (P < 0.01) between both films. Fitting equation of the calibration curve is shown below. y = -390.47 �� 200 + (443.45 �� 10x80).5068 �� 0.0434.
Conclusion: Based on the relationship between the sensitivity of the active layer to UV-A rays and the strength of UV protection on the surface, we concluded that backside irradiation is recommended for Gafchromic XR-QA2, and frontside irradiation is recommended for Gafchromic RTQA2.
