Abstract
OBJECTIVE: The U.S. Centers for Medicare & Medicaid Services (CMS) recently approved the use of low-dose CT for lung cancer screening and described volumetric CT dose index (CTDI(vol)) requirements. These were based on the National Lung Screening Trial, which used only fixed-tube-current techniques. The aim of this study was to evaluate dose index data from a lung cancer screening program using automatic exposure control (AEC) techniques to ensure compliance with requirements and to correlate dose index values with patient size. MATERIALS AND METHODS: CTDI(vol), dose-length product (DLP), and body mass index (BMI) data were collected for 563 lung cancer screening examinations performed with AEC between January 1, 2014, through August 31, 2015. CTDI(vol) and DLP were analyzed according to the patient's BMI classification. Results were compared with the CMS requirement that the CTDI(vol) for a standard-sized patient (height, 170 cm; weight, 70 kg) be 3.0 mGy or less, with adjustments for patients of different sizes. For a subset of patients, the average water-equivalent diameter and size-specific dose estimate were estimated. RESULTS: The average CTDI(vol) for a standard-sized patient was 1.8 mGy, which meets CMS requirements. CTDI(vol) values were lower for smaller patients and higher for larger patients. Overall, the mean CTDI(vol) and DLP were 2.1 mGy and 74 mGy⋅cm, respectively. The size-specific dose estimate for the average water-equivalent diameter (27.5 cm) of the patient subset was 2.6 mGy. CONCLUSION: The screening protocols using AEC resulted in CTDI(vol) values that were compliant with CMS requirements. CTDI(vol) values greater than 3.0 mGy were only observed for overweight or obese patients.