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Radiation Risk From Lung Cancer ScreeningRadiation Risk From Lung Cancer Screening: Glowing in the Dark? FREE TO VIEW

David C. Christiani, MD, MPH, FCCP
Author and Funding Information

From the Harvard School of Public Health, and Massachusetts General Hospital/Harvard Medical School.

Correspondence to: David C. Christiani, MD, MPH, FCCP, Harvard School of Public Health, 665 Huntington Ave, I-1401, Boston, MA 02115; e-mail: dchris@hsph.harvard.edu


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

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2014;145(3):439-440. doi:10.1378/chest.13-2588
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The introduction of helical (spiral) CT scanning in the late 1980s revolutionized diagnostic medical imaging. Single-detector row CT scanners and, more recently, multidetector row CT scanners markedly increased the clinical indications for CT imaging and resulted in more CT imaging examinations being performed. The introduction of low-dose spiral CT (LDCT) scanning led to increased screening for lung lesions in asymptomatic individuals at high risk for lung cancer. Subsequently, clinical trials were undertaken to evaluate the use of LDCT screening.

In a 2007 editorial for the British Medical Journal, my colleague and I called for caution in adapting widespread use of LDCT scanning for lung cancer screening pending the results of randomized clinical trials, lest we make the same errors as with mammograms.1 The trials have now been done, and the results show a significant survival benefit from three annual screenings with LDCT scan in a population with specific characteristics (ie, those aged > 55 years who have smoked cigarettes at a cumulative dose of ≥ 30 pack-years and, if a former smoker, < 15 years quit2), reducing lung cancer mortality by 20% and overall mortality by 7%. Another article from the same trial—the National Lung Cancer Screening Trial (NLST)—showed that two annual incidence screenings with LDCT scan results in fewer advanced stage and more early stage cancers diagnosed.3 An accompanying trial by the Pan-Canadian Early Detection of Lung Cancer Study and British Columbia Cancer Agency that assessed the probability of cancer in nodules detected on LDCT scan showed that combining predictive variables, including older age, sex, family history, emphysema, larger nodule size, location in upper lobe, part-solid type, lower nodule count, and speculation, with LDCT scan increased the positive predictive value of baseline screening LDCT scan for cancer.4 In fact, the data suggested that in a population with the same age and exposure characteristics as that of the NLST, the cost-benefit ratio from lung cancer screening with LDCT scan is larger than that of current mammogram screening programs for breast cancer.5

The largest reduction in lung cancer mortality in the United States now comes from smoking cessation. However, smoking cessation alone is not a panacea; one-half of lung cancers are diagnosed in former smokers, so screening for lung cancer is needed, and imaging offers the best approach. In the future, biomarkers (eg, proteomic or metabolomic patterns) used alone or in conjunction with an imaging-based technology, such as CT scanning, may help to identify early stage lung cancers. In addition, genetic markers could be used to identify people at high risk for lung cancer who would benefit from more intensive screening. However, we currently have no evidence that any of these technologies help with early detection, leaving LDCT scan as the best option. When an abnormality is found on LDCT scanning, patients undergo full-dose diagnostic CT scans that have at least fourfold more radiation effective dose.

A persistent concern of many professionals in the medical and public health communities is that in the rapidly evolving field of multidetector row CT imaging, issues of radiation dose may have been diminished in the quest for increased image quality, diagnostic accuracy, and new imaging techniques.6 Hence, the issue of patient radiation exposure, including estimated cumulative dose from multiple examinations for systematic screening and follow-up testing, is investigated in the article by McCunney and Li7 in this issue of CHEST (see page 618). They compared the risk of a typical patient in an LDCT screening program (three full-dose CT scans performed in screen-positive patients) with that of atomic bomb survivors and occupational exposures in the nuclear industry. Despite obvious differences in the populations being compared (acute, high-dose exposure in the case of bomb survivors and chronic, low-level exposures in nuclear industry workers), the contrasts allow some perspective on the issue. With the use of estimates of lifelong radiation exposure and effective dose, the authors found that long-term (20-30 years) LDCT screening programs are associated with nontrivial cumulative radiation doses that may exceed occupational or atomic bomb exposure and independently increase risk of lung cancer due to cumulative radiation exposure.

A key aspect in this analysis is the estimation of effective dose. Effective dose is calculated by summing the absorbed doses to individual organs weighted for their radiation sensitivity. Effective dose has limitations because it represents the radiation detriment for the general population or the specific population of radiation workers and may not be appropriate for many patient populations. Hence, there may well be exposure misclassification in the estimates used by McCunney and Li7 for actual lung dose. However, effective dose remains the best measurement available. Because it is not possible to measure the absorbed dose inside a patient, it is not feasible to calculate the exact effective dose for each patient examination. Moreover, the authors focused on internal dose (ie, lung) as the main target when chest exposures can also expose breast tissues and bone marrow to substantial levels of radiation. However, it is possible to make a reasonable estimate of the effective chest, and hence lung, dose.

McCunney and Li’s7 choice of radiation industry workers and atomic bomb survivors is somewhat sensational. Although common sense might suggest that radiation workers and atom bomb survivors have the worst average radiation exposure, this is not the case. For example, airline flight crews are exposed to excess cosmic radiation. Their occupational exposure is about 2 to 5 mSv/y. Over the course of a 30-year career, that would be about 60 to 150 mSv, which easily exceeds the average long-term radiation exposures for radiation workers (mostly < 30 mSv) and atomic bomb survivors (40 mSv) that McCunney and Li7 quote.

The issue at this point is not that LDCT scanning risk outweighs its benefits. However, tests should be ordered using best-evidence clinical indications, namely restricted use to populations with the same age and smoking profile as that in the NLST and, ideally, including optimization with a predictive algorithm.

A position paper by the Fleischner Society a decade ago remains relevant today.6 The radiation effective dose from diagnostic CT scans is high, and further research is needed into the complex relationship among radiation exposure, image noise, and diagnostic accuracy to establish scientifically the minimum radiation doses that provide adequate diagnostic information for clinical practice and to automate procedures to ensure that exposures occur as low as reasonably achievable. The challenge to the makers of CT scanners is to produce excellent image quality but at the radiation dose level of an LDCT scan, and the challenge to clinicians is to restrict screening to patients with the appropriate risk factors.

References

McMahon PM, Christiani DC. Computed tomography screening for lung cancer. BMJ. 2007;334(7588):271. [CrossRef] [PubMed]
 
Aberle DR, Adams AM, Berg CD, et al; National Lung Screening Trial Research Team. Reduced lung-cancer mortality with low-dose computed tomographic screening. N Engl J Med. 2011;365(5):395-409. [CrossRef] [PubMed]
 
Aberle DR, DeMello S, Berg CD, et al; National Lung Screening Trial Research Team. Results of the two incidence screenings in the National Lung Screening Trial. N Engl J Med. 2013;369(10):920-931. [CrossRef] [PubMed]
 
McWilliams A, Tammemagi MC, Mayo JR, et al. Probability of cancer in pulmonary nodules detected on first screening CT. N Engl J Med. 2013;369(10):910-919. [CrossRef] [PubMed]
 
de Koning HJ, Meza R, Plevritis SK, et al. Benefits and harms of computed tomography lung cancer screening programs for high-risk populations. AHRQ Publication No. 13-05196-EF-2. US Preventive Services Task Force website.http://www.uspreventiveservicestaskforce.org/uspstf13/lungcan/lungcanmodeling.htm. July 2013. Accessed October 31, 2013.
 
Mayo JR, Aldrich J, Muller NL; Fleischner Society. Radiation exposure at chest CT: a statement of the Fleischner Society. Radiology. 2003;228(1):15-21. [CrossRef] [PubMed]
 
McCunney RJ, Li J. Radiation risks in lung cancer screening programs: a comparison with nuclear industry workers and atomic bomb survivors. Chest. 2014;145(3):618-624.
 

Figures

Tables

References

McMahon PM, Christiani DC. Computed tomography screening for lung cancer. BMJ. 2007;334(7588):271. [CrossRef] [PubMed]
 
Aberle DR, Adams AM, Berg CD, et al; National Lung Screening Trial Research Team. Reduced lung-cancer mortality with low-dose computed tomographic screening. N Engl J Med. 2011;365(5):395-409. [CrossRef] [PubMed]
 
Aberle DR, DeMello S, Berg CD, et al; National Lung Screening Trial Research Team. Results of the two incidence screenings in the National Lung Screening Trial. N Engl J Med. 2013;369(10):920-931. [CrossRef] [PubMed]
 
McWilliams A, Tammemagi MC, Mayo JR, et al. Probability of cancer in pulmonary nodules detected on first screening CT. N Engl J Med. 2013;369(10):910-919. [CrossRef] [PubMed]
 
de Koning HJ, Meza R, Plevritis SK, et al. Benefits and harms of computed tomography lung cancer screening programs for high-risk populations. AHRQ Publication No. 13-05196-EF-2. US Preventive Services Task Force website.http://www.uspreventiveservicestaskforce.org/uspstf13/lungcan/lungcanmodeling.htm. July 2013. Accessed October 31, 2013.
 
Mayo JR, Aldrich J, Muller NL; Fleischner Society. Radiation exposure at chest CT: a statement of the Fleischner Society. Radiology. 2003;228(1):15-21. [CrossRef] [PubMed]
 
McCunney RJ, Li J. Radiation risks in lung cancer screening programs: a comparison with nuclear industry workers and atomic bomb survivors. Chest. 2014;145(3):618-624.
 
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