Radiation Dose Reduction in Low-Dose Chest Computed Tomography Using Precise Topography-Based Scan Range Selection

Wei-Ming Huang ； Sho-Ting Hung ； Keng-Qiang Chen ； Chin-Yin Sheu ； Shin-Lin Shih ； Chun-Chao Huang

《Journal of Radiological Science》 43卷 (2018/03) Pp. 19-26

https://doi.org/10.6698/JRS.201806_43.0004

摘要

PURPOSE. Low-dose chest computed tomography (LDCT) is currently the best tool for early detection of lung cancer. However, accumulated radiation exposure may causes undetermined risk to health. One method to reduce the radiation dose received during computed tomography (CT) is to minimize the scan range. Previous studies have offered no concrete method to achieve that. This study offers a new method for setting a minimal but adequate scan range to avoid unnecessary radiation exposure during LDCT. MATERIALS AND METHODS. We enrolled 50 patients receiving LDCT. All CT scans were performed under one CT scanner (Aquilion ONE, Toshiba Medical Systems, Otawara, Japan). We retrospectively calculated the minimum necessary scan range for CT localizer radiography (topography). We compared different methods using posterior-anterior (PA) topography and lateral topography and considered different patient characteristics, such as gender and body mass index (BMI). We excluded cases with incomplete records or the images that were difficult to interpret. RESULTS. Regardless of patient characteristics, we successfully obtained adequate scan range and reduced radiation dosage by setting the upper limit of the scan as 9 mm more than the first slice of lung apex on PA topography and the lower limit of the scan as 19 mm lower than the last slice of basal lung on lateral topography. The average radiation dosage could be reduced by 12.75%, meaning the average effective dose could be decreased from 0.95 mGy to 0.83 mGy. Taking patient characteristics into consideration, dividing patients into the subgroup by female/BMI ≥ 24 and using lateral view of the topography to set the lower limit of the scan could achieve the maximum dose reduction (17.47%). However, we found that using lateral topography instead of PA topography to set the lower limit of the scan not only produced a lower radiation dose but also overcame the effects of different patient characteristics. CONCLUSION. Setting the LDCT scan range as 9 mm more than the first slice of lung apex on PA topography and 19 mm lower than the last slice of basal lung on lateral topography permits adequate imaging and minimal radiation dose. Using lateral topography to set the lower limit of the lung is the most important factor for minimizing the scan range of LDCT and to avoid unnecessary radiation exposure.

關鍵字

CT localizer radiography ； length of scan ； low dose lung computed tomography ； radiation dose ； topography