Chest
Volume 145, Issue 3, March 2014, Pages 618-624
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Special Features
Radiation Risks in Lung Cancer Screening Programs

https://doi.org/10.1378/chest.13-1420Get rights and content

The National Lung Cancer Screening Trial (NLST) demonstrated that screening with low-dose CT (LDCT) scan reduced lung cancer and overall mortality by 20% and 7%, respectively. The LDCT scanning involves an approximate 2-mSv dose, whereas full-chest CT scanning, the major diagnostic study used to follow up nodules, may involve a dose of 8 mSv. Radiation associated with CT scanning and other diagnostic studies to follow up nodules may present an independent risk of lung cancer. On the basis of the NLST, we estimated the incidence and prevalence of nodules detected in screening programs. We followed the Fleischner guidelines for follow-up of nodules to assess cumulative radiation exposure over 20- and 30-year periods. We then evaluated nuclear worker cohort studies and atomic bomb survivor studies to assess the risk of lung cancer from radiation associated with long-term lung cancer screening programs. The findings indicate that a 55-year-old lung screening participant may experience a cumulative radiation exposure of up to 280 mSv over a 20-year period and 420 mSv over 30 years. These exposures exceed those of nuclear workers and atomic bomb survivors. This assessment suggests that long-term (20-30 years) LDCT screening programs are associated with nontrivial cumulative radiation doses. Current lung cancer screening protocols, if conducted over 20- to 30-year periods, can independently increase the risk of lung cancer beyond cigarette smoking as a result of cumulative radiation exposure. Radiation exposures from LDCT screening and follow-up diagnostic procedures exceed lifetime radiation exposures among nuclear power workers and atomic bomb survivors.

Section snippets

Materials and Methods

The NLST was used as the primary lung cancer screening reference because recommendations for screening by the American College of Chest Physicians and the American Society of Clinical Oncology have been based on this study.2, 3 Participants were aged 55 to 74 years, had a ≥ 30-pack-year smoking history, and were current smokers or former smokers who quit in the past 15 years.

Screenings yielding noncalcified nodules > 4 mm necessitated diagnostic follow-up, with full CT scan initially. The size

Assumptions on the Prevalence and Incidence of Nodules Detected in Lung Cancer Screening

Up to 50% of smokers aged > 50 years have pulmonary nodules.11, 13 A significant heterogeneity has been noted in the percentage of nodules detected at incidence and prevalence in lung cancer screening programs. We chose to use the range of 25% to 50% for both incidence and prevalence of nodules detected on LDCT scan on the basis of several studies.2, 3, 6, 8, 9 Incidence of nonpulmonary conditions warranting follow-up averaged about 5% in lung cancer screening programs.9

Radiation Doses From LDCT Scanning and CT Scanning

Radiation exposure is measured by a number of units, including sieverts and grays. The sievert reflects the effective dose and represents the stochastic biologic effects of ionizing radiation. One sievert equals 100 rem (roentgen equivalent man), an older radiation metric. The gray is the radiation measure used to reflect the absorbed dose.

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

Assessing Risk of Occupational Radiation Exposure

We addressed chronic low-dose radiation risks by reviewing nuclear worker cohort studies in which the risk of lung cancer was evaluated in light of total ionizing radiation exposure. We also used atomic bomb survivor data to assess acute high-dose radiation exposure risk.

Determining Cumulative Dose of Ionizing Radiation in Lung Cancer Screening Programs

Different scenarios were used to estimate the cumulative radiation exposure from screening over 20- to 30-year periods. The primary variables were (1) percentage of nodules detected on LDCT scan requiring follow-up, (2) radiation doses associated with screening and diagnostic studies, and (3) length of the screening program (20 vs 30 years). We considered 30 years as reflective of starting screening at age 50 and stopping at age 80. These assumptions were made to simplify the estimation of

Estimating Cumulative Radiation Exposure From Lung Cancer Screening Programs

If a 4-mm nodule is detected per LDCT scan, an additional three CT scans are recommended before concluding that the nodule is benign. These additional full CT scans per 4-mm nodule detected add another 24 mSv of radiation exposure. If a 4-mm nodule is detected every 2 years, the cumulative radiation exposure would be 2 mSv per year over 20 years (40 mSv) for the LDCT scans and 24 mSv per follow-up for each 4-mm nodule detected. Thus, over a 20-year period (ages 55-75 years), the cumulative

Conclusions

Of the 90 million current and former smokers in the United States, about 8 to 8.7 million adults meet the NLST criteria for lung cancer screening with LDCT scan.3, 30, 31, 32 Thus, lung cancer screening may involve a substantial number of people, which makes clarifying the risks and benefits of screening of paramount importance.

We evaluated cumulative radiation doses for lung cancer screening participants from the LDCT scan to follow-up full CT scan and FNAB according to the incidence and

Acknowledgments

Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

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