Body Size-Specific Organ and Effective Doses of Chest CT Screening Examinations of the National Lung Screening Trial

OBJECTIVE. We calculated body size-specific organ and effective doses for 23,734 participants in the National Lung Screening Trial (NLST) using a CT dose calculator. MATERIALS AND METHODS. We collected participant-specific technical parameters of 23,734 participants who underwent CT in the clinical trial. For each participant, we calculated two sets of organ doses using two methods. First, we computed body size-specific organ and effective doses using the National Cancer Institute CT (NCICT) dosimetry program, which is based on dose coefficients derived from a library of body size-dependent adult male and female computational phantoms. We then recalculated organ and effective doses using dose coefficients from reference size phantoms for all examinations to investigate potential errors caused by the lack of body size consideration in the dose calculations. RESULTS. The underweight participants (body mass index [BMI; weight in kilograms divided by the square of height in meters] < 18.5) received 1.3-fold greater lung dose (median, 4.93 mGy) than the obese participants (BMI > 30) (3.90 mGy). Thyroid doses were approximately 1.3-to 1.6-fold greater than the lung doses (6.3-6.5 mGy). The reference phantombased dose calculation underestimates the body size-specific lung dose by up to 50% for the underweight participants and overestimates that value by up to 200% for the overweight participants. The median effective dose ranges from 2.01 mSv in obese participants to 2.80 mSv in underweight participants. CONCLUSION. Body size-specific organ and effective doses were computed for 23,734 NLST participants who underwent low-dose CT screening. The use of reference size phantoms can lead to significant errors in organ dose estimates when body size is not considered in the dose assessment.