In the NLST, the estimated effective doses of LDCT and CT scans were 2 mSv and 7 to 8 mSv, respectively; about 10% of the LDCT scans were associated with radiation exposures between 2 and 4 mSv.14 Brenner15 estimated the LDCT scan dose to be 5.2 mGy, which is based on an earlier study that indicated that lung doses vary from 2.5 to 9.0 mGy. In a study of 31,642 patients who underwent CT scanning examinations in 2007, the effective dose was 8 mSv.16 These dose estimates for LDCT scanning, however, are higher than those estimated from the NLST, which estimated doses for LDCT scans to be about 2 mSv.14 Values reported in the scientific literature have ranged from 4 to 18 mSv.17 A CT image-guided FNAB has an estimated effective dose of 1.5 mSv.18 Natural background radiation ranges from 2.4 to 3 mSv per year.17 In the NLST, any nodule > 4 mm was evaluated as follows: chest CT scan (73%), fluorodeoxyglucose PET-CT scan (10%), and FNAB (2.2%). In the first round of NLST, 7,191 positive tests (ie, a nodule > 4 mm) were noted. Among those with positive test results, lung cancer was noted in 3.8%. Thus, 96.2% of the nodules were false positive. Of the 693 people with lung cancer detected, 649 (93.6%) had a positive LDCT scan. Forty-four people (6.4%) with lung cancer had a negative LDCT scan, reflecting false-negative test results. Among these 44 people with lung cancer who had a normal LDCT scan, 15 (35%) had small cell carcinoma.