[P020] The influence of phantom diameter on X-ray CT dose evaluation using radiochromic film. (August 2018) - Tanki, Nobuyoshi
Abstract : Purpose: In recent years, one of most important topic for X-ray CT examination is reducing radiation exposure. We have tried to establish the simple and accurate CT dosimetry method using radiochromic (RC) film. In this study, we investigated how the phantom diameter affects the pixel value distribution of RC film. This research is one step of quantifying dose distribution of X-ray CT using RC film. Methods: The radiochromic film was exposed by a clinical CT scanner (Aquilion Lightning, Toshiba Medical Systems). Gafchromic XR-QA2 film was irradiated. The film-folding phantom consists of two acrylic semicylinder. In this study, the large phantom (cylinder cross-section diameter is 16 cm) and the small phantom (cylinder cross-section diameter is 10 cm) were used in this research. The scan parameters were as follows: non-helical scan, tube voltage = 120 kV, tube current = 300 mA, slice thickness = 2 cm, scan speed = 1 s per rotation. Image processing and analysis were performed by MATLAB (The Mathworks, Inc.) and Image J (National Institute of Health). The irradiated films were scanned by a commercial scanner (EPSON ES-10000G, Seiko Epson Co.). Results: To compare the pixel value distribution using two differently sized phantom, we used the contour line analysis. The differences of distribution were observed between the large phantom and the small phantom. It was found that the distribution using the large phantom changes clearly. Conclusions: In conclusion, our method may be useful for analyzing the distribution of pixel value on various conditions.