The effect of exposure technique on image quality and radiation dose from CT simulation image of chest (phantom study)

Introduction: Computed tomography simulation imaging is a processing for treatment plan that may cause patients high radiation dose receiving. Thus, exposure techniques variation could reduce dose risk. Objectives: Purpose of this study was to study effect of exposure technique on image quality and radiation dose (CTDIvol and effective dose) from CT simulation image of chest. Materials and methods: Exposure parameters (tube voltage, tube current and slice thickness) were varied to achieve low radiation dose with equal reference image quality (120 kVp, 100 mAs). In this study, chest phantom was used. Scanning parameters were 90, 120,140 kVp, in which each kVp was varied to 50, 100, 150 mAs and slice thickness at 3 mm and 5 mm were tested. CTDIvol from each scan was recorded. Effective dose of chest and breast was calculated by impact scan program. Image noise was measured in lung and heart regions. Image quality was evaluated by 2 radiation oncologists. Results: The results showed that kVp and mAs were affected to radiation dose. mAs was direct proportional to while kVp increased radiation dose. In addition, image noise measured in heart and lung region with increasing kVp or mAs, were reduced. Moreover, 3 mm-slice thickness showed higher noise than 5 mm-slice thickness. Conclusion: The recommended exposure parameters for computed tomography simulation assessed by radiation oncologists were 140 kVp, 50 mAs for 3 mm- and 5 mm-slice thickness, respectively. The radiation dose reduced 26.35% (5.92 to 4.36 mGy) from reference exposure technique. Effective dose of chest and breast were 0.7 and 0.57 mSv, respectively. Bull Chiang Mai Assoc Med Sci 2016; 49(2): 245-254. Doi: 10.14456/jams.2016.16