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POINT: Should Radiation Dose From CT Scans Be a Factor in Patient Care? YesRadiation Dose a Factor in Patient Care? Yes FREE TO VIEW

Robert J. McCunney, MD, MPH
Author and Funding Information

From Brigham and Women’s Hospital.

CORRESPONDENCE TO: Robert J. McCunney, MD, MPH, Brigham and Women’s Hospital, 75 Francis St, Boston, MA 02215; e-mail: mccunney@mit.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. 2015;147(4):872-874. doi:10.1378/chest.14-3020
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Published online

How radiation from a CT scan should be considered in patient care depends upon the circumstances in which the test is conducted. Ionizing radiation, the adverse health effects from which are cumulative, should be minimized but used when appropriate.

Chest CT scans are used primarily for diagnostic purposes but also for monitoring disease and screening for asymptomatic disease. The challenge regarding radiation risks is to address the purpose of the CT scan. In evaluating pulmonary embolism, chest injuries, and other life-threatening conditions, radiation exposure is a trivial factor. In evaluating hemoptysis, chronic shortness of breath, and symptoms that may reflect malignancies, radiation exposure needs to yield to obtaining important diagnostic information. In screening for lung cancer, however, radiation exposure should be considered in evaluating benefits and risks of the CT scan.

The National Lung Screening Trial (NLST) demonstrated a 20% reduction in lung cancer mortality by periodic screening with low-dose CT (LDCT) scanning.1 Other prospective studies, albeit of smaller and shorter duration, have not shown reductions in lung cancer mortality.2,3 Nonetheless, as a result of the high incidence and mortality of lung cancer and the number of cigarette smokers at risk, many organizations have recommended LDCT scanning for screening, according to the entry criteria of the NLST: age from 55 to 74 years, 30 pack-year smoking history, and, for ex-smokers, those who have quit within the previous 15 years.4

The NLST lasted just over 3 years, but the eligibility criteria span 20 years, so upon reaching age 55, eligible patients may have another 20 years of screening ahead, including the corresponding follow-up full-chest CT scans and other diagnostic studies, involving ionizing radiation exposure. In light of the age-related incidence of lung cancer, it is not unreasonable to expect that screening will continue beyond age 74 and that “slippage” in the eligibility criteria may occur as people younger than age 55 and those with less than a 30 pack-year history seek screening.

The US Preventive Services Task Force stated: “If LDCT becomes routine, it will be important to measure the risk of radiation-associated harms and identify methods to lower the dose.”4 Radiation dose from a CT scan depends primarily on the CT scan machine itself, the number of images obtained, and the body habitus of the patient.5 Some studies offer a perspective about long-term health risks associated with ionizing radiation: An evaluation of cancer risk from CT scans conducted in 2007 concluded that an additional 4,100 cases of cancer would result.6 Most studies suggest that the additional risk of lung cancer from periodic LDCT scans is not trivial and approximates an additional 1% increase in lung cancer; if this risk is considered in light of the upwards of 8 million people who meet NLST criteria, tens of thousands of additional cases of lung cancer would occur.7

Radiation dose from chest CT scans may vary from 2 to 20 mSv.8 In the NLST, the effective dose per LDCT averaged 2 mSv, whereas in the ITALUNG trial, the effective dose was 3.6 mSv.9 Further adding to the complexity of assessing radiation risks from lung cancer screening is the synergistic effect between cigarette smoking and radiation exposure.

Nodule size is the most important prognostic factor in lung cancer.10 The follow-up of nodules can lead to substantial radiation exposure in long-term screening programs.11 Thus, an enhanced refinement of what constitutes a positive result of a nodule and appropriate time intervals for follow-up testing are critical factors in reducing cumulative radiation exposure. For example, is it necessary to follow up 4-mm nodules? Can follow-up be limited to nodules > 4 mm, the size prompting follow-up in the NLST? A study suggested considerable declines in false-positive results if the criterion for the diameter of nodules requiring diagnostic follow-up is modified.12 When using 5, 6, 7, 8 and 9 mm as the criteria for follow-up, false-positive tests declined 16%, 10.2%, 7.1%, 5.1%, and 4%, respectively.12 Very small nodules, (ie, those < 5 mm in diameter) have a slight risk of malignancy (three of 230 nodules in one series).13 Would a volumetric assessment of nodules be more precise in determining nodules of clinical relevance?14,15 The UK Lung Cancer Screening Study and the NELSON Trial used a volumetric approach to assess the significance of nodules.15

Is it necessary to perform follow up of nodules > 4 mm every 3 to 6 months? Would more precise estimations of tumor doubling times be of value in determining frequency of interval CT scans? Should the Fleischner guidelines be reviewed in light of the NLST results?16 Evaluating lung cancer cases in the NLST in terms of nodule presentation and follow-up would help answer these questions. The availability of these data can be helpful in further characterizing both the significance and growth rates of nodules of clinical importance, including those considered to be “overdiagnosed.” In fact, overdiagnosis detection of nodules with no effect on patient mortality may account for upwards of 20% to 25% of lung cases diagnosed in screening programs.17 If these data on overdiagnosis prove reproducible, the risk benefit of LDCT screening will also change. Importantly, further reductions in radiation exposure may be possible through equipment design and enclosures, and further reductions in radiation could be effected through careful control of voltage used to enable sufficient resolution of images for noting nodules of clinical importance.

The challenge for clinicians is to apply aggregate data from studies of upwards of 25,000 people to the patient. Applying epidemiologic data to the patient requires expertise and judgment, a classic challenge in health care. In screening large numbers of people with LDCT scan, small increases in risk from cumulative radiation may result in large numbers of avoidable cancer, because of the millions of people who meet eligibility criteria for LDCT scan screening.4,7 The major risk factors for lung cancer are smoking intensity and duration, family history of lung cancer, advancing age, and the presence of COPD.18,19 Despite these efforts at defining risks and benefits of screening, the data are not sufficiently practical to use in clinical care.

Risks of lung cancer associated with ionizing radiation need to be addressed with care, since screening tests are conducted on people without symptoms and without apparent disease and in whom cancer may never develop. The NLST demonstrated that 320 people need to be screened annually for 3 years to prevent one lung cancer death.20

How does a clinician advise their patient regarding LDCT scanning? As always, effective communication about benefits and risks is paramount. Advise patients that the NLST showed that one of every four to five people who undergo testing will have a positive test and that one of 25 patients with positive test results will have lung cancer. For those who do not meet the NLST criteria, it is unclear whether LDCT will reduce mortality from lung cancer. What is perfectly clear, however, is that cigarette smoking is associated with accelerated decline in lung function, COPD, and lung cancer. Efforts aimed at improved rates of cigarette-smoking cessation will have the most impact in reducing mortality from lung cancer.

LDCT

low-dose CT

LDR

low-dose radiation

LNT

linear no-threshold

NLST

National Lung Screening Trial

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]
 
Pastorino U, Rossi M, Rosato V, et al. Annual or biennial CT screening versus observation in heavy smokers: 5-year results of the MILD trial. Eur J Cancer Prev. 2012;21(3):308-315. [CrossRef] [PubMed]
 
Saghir Z, Dirksen A, Ashraf H, et al. CT screening for lung cancer brings forward early disease. The randomised Danish Lung Cancer Screening Trial: status after five annual screening rounds with low-dose CT. Thorax. 2012;67(4):296-301. [CrossRef] [PubMed]
 
Humphrey LL, Deffebach M, Pappas M, et al. Screening for lung cancer with low-dose computed tomography: a systematic review to update the US Preventive Services Task Force recommendation. Ann Intern Med. 2013;159(6):411-420. [CrossRef] [PubMed]
 
Marshall HM, Bowman RV, Yang IA, Fong KM, Berg CD. Screening for lung cancer with low-dose computed tomography: a review of current status. J Thorac Dis. 2013;5(suppl 5):S524-S539. [PubMed]
 
Berrington de González A, Mahesh M, Kim KP, et al. Projected cancer risks from computed tomographic scans performed in the United States in 2007. Arch Intern Med. 2009;169(22):2071-2077. [CrossRef] [PubMed]
 
Brenner DJ. Radiation risks potentially associated with low-dose CT screening of adult smokers for lung cancer. Radiology. 2004;231(2):440-445. [CrossRef] [PubMed]
 
Mettler FA Jr, Huda W, Yoshizumi TT, Mahesh M. Effective doses in radiology and diagnostic nuclear medicine: a catalog. Radiology. 2008;248(1):254-263. [CrossRef] [PubMed]
 
Mascalchi M, Mazzoni LN, Falchini M, et al. Dose exposure in the ITALUNG trial of lung cancer screening with low-dose CT. Br J Radiol. 2012;85(1016):1134-1139. [CrossRef] [PubMed]
 
Gohagan J, Marcus P, Fagerstrom R, Pinsky P, Kramer B, Prorok P; Writing Committee, Lung Screening Study Research Group. Baseline findings of a randomized feasibility trial of lung cancer screening with spiral CT scan vs chest radiograph: the Lung Screening Study of the National Cancer Institute. Chest. 2004;126(1):114-121. [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. [CrossRef] [PubMed]
 
Henschke CI, Yip R, Yankelevitz DF, Smith JP; International Early Lung Cancer Action Program Investigators. Definition of a positive test result in computed tomography screening for lung cancer: a cohort study. Ann Intern Med. 2013;158(4):246-252. [CrossRef] [PubMed]
 
Bellomi M, Veronesi G, Rampinelli C, Ferretti S, De Fiori E, Maisonneuve P. Evolution of lung nodules < or =5 mm detected with low-dose CT in asymptomatic smokers. Br J Radiol. 2007;80(957):708-712. [CrossRef] [PubMed]
 
van Klaveren RJ, Oudkerk M, Prokop M, et al. Management of lung nodules detected by volume CT scanning. N Engl J Med. 2009;361(23):2221-2229. [CrossRef] [PubMed]
 
Baldwin DR, Hansell DM, Duffy SW, Field JK. Lung cancer screening with low dose computed tomography. BMJ. 2014;348:g1970. [CrossRef] [PubMed]
 
MacMahon H, Austin JHM, Gamsu G, et al. Guidelines for management of small pulmonary nodules detected on CT scans: a statement from the Fleischner Society. Radiology. 2005;237(2):395-400. [CrossRef] [PubMed]
 
Veronesi G, Maisonneuve P, Bellomi M, et al. Estimating overdiagnosis in low-dose computed tomography screening for lung cancer: a cohort study. Ann Intern Med. 2012;157(11):776-784. [CrossRef] [PubMed]
 
Tammemägi MC, Katki HA, Hocking WG, et al. Selection criteria for lung-cancer screening. N Engl J Med. 2013;368(8):728-736. [CrossRef] [PubMed]
 
Kovalchik SA, Tammemagi M, Berg CD, et al. Targeting of low-dose CT screening according to the risk of lung-cancer death. N Engl J Med. 2013;369(3):245-254. [CrossRef] [PubMed]
 
O’Connor GT, Hatabu H. Lung cancer screening, radiation, risks, benefits, and uncertainty. JAMA. 2012;307(22):2434-2435. [CrossRef] [PubMed]
 

Figures

Tables

References

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]
 
Pastorino U, Rossi M, Rosato V, et al. Annual or biennial CT screening versus observation in heavy smokers: 5-year results of the MILD trial. Eur J Cancer Prev. 2012;21(3):308-315. [CrossRef] [PubMed]
 
Saghir Z, Dirksen A, Ashraf H, et al. CT screening for lung cancer brings forward early disease. The randomised Danish Lung Cancer Screening Trial: status after five annual screening rounds with low-dose CT. Thorax. 2012;67(4):296-301. [CrossRef] [PubMed]
 
Humphrey LL, Deffebach M, Pappas M, et al. Screening for lung cancer with low-dose computed tomography: a systematic review to update the US Preventive Services Task Force recommendation. Ann Intern Med. 2013;159(6):411-420. [CrossRef] [PubMed]
 
Marshall HM, Bowman RV, Yang IA, Fong KM, Berg CD. Screening for lung cancer with low-dose computed tomography: a review of current status. J Thorac Dis. 2013;5(suppl 5):S524-S539. [PubMed]
 
Berrington de González A, Mahesh M, Kim KP, et al. Projected cancer risks from computed tomographic scans performed in the United States in 2007. Arch Intern Med. 2009;169(22):2071-2077. [CrossRef] [PubMed]
 
Brenner DJ. Radiation risks potentially associated with low-dose CT screening of adult smokers for lung cancer. Radiology. 2004;231(2):440-445. [CrossRef] [PubMed]
 
Mettler FA Jr, Huda W, Yoshizumi TT, Mahesh M. Effective doses in radiology and diagnostic nuclear medicine: a catalog. Radiology. 2008;248(1):254-263. [CrossRef] [PubMed]
 
Mascalchi M, Mazzoni LN, Falchini M, et al. Dose exposure in the ITALUNG trial of lung cancer screening with low-dose CT. Br J Radiol. 2012;85(1016):1134-1139. [CrossRef] [PubMed]
 
Gohagan J, Marcus P, Fagerstrom R, Pinsky P, Kramer B, Prorok P; Writing Committee, Lung Screening Study Research Group. Baseline findings of a randomized feasibility trial of lung cancer screening with spiral CT scan vs chest radiograph: the Lung Screening Study of the National Cancer Institute. Chest. 2004;126(1):114-121. [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. [CrossRef] [PubMed]
 
Henschke CI, Yip R, Yankelevitz DF, Smith JP; International Early Lung Cancer Action Program Investigators. Definition of a positive test result in computed tomography screening for lung cancer: a cohort study. Ann Intern Med. 2013;158(4):246-252. [CrossRef] [PubMed]
 
Bellomi M, Veronesi G, Rampinelli C, Ferretti S, De Fiori E, Maisonneuve P. Evolution of lung nodules < or =5 mm detected with low-dose CT in asymptomatic smokers. Br J Radiol. 2007;80(957):708-712. [CrossRef] [PubMed]
 
van Klaveren RJ, Oudkerk M, Prokop M, et al. Management of lung nodules detected by volume CT scanning. N Engl J Med. 2009;361(23):2221-2229. [CrossRef] [PubMed]
 
Baldwin DR, Hansell DM, Duffy SW, Field JK. Lung cancer screening with low dose computed tomography. BMJ. 2014;348:g1970. [CrossRef] [PubMed]
 
MacMahon H, Austin JHM, Gamsu G, et al. Guidelines for management of small pulmonary nodules detected on CT scans: a statement from the Fleischner Society. Radiology. 2005;237(2):395-400. [CrossRef] [PubMed]
 
Veronesi G, Maisonneuve P, Bellomi M, et al. Estimating overdiagnosis in low-dose computed tomography screening for lung cancer: a cohort study. Ann Intern Med. 2012;157(11):776-784. [CrossRef] [PubMed]
 
Tammemägi MC, Katki HA, Hocking WG, et al. Selection criteria for lung-cancer screening. N Engl J Med. 2013;368(8):728-736. [CrossRef] [PubMed]
 
Kovalchik SA, Tammemagi M, Berg CD, et al. Targeting of low-dose CT screening according to the risk of lung-cancer death. N Engl J Med. 2013;369(3):245-254. [CrossRef] [PubMed]
 
O’Connor GT, Hatabu H. Lung cancer screening, radiation, risks, benefits, and uncertainty. JAMA. 2012;307(22):2434-2435. [CrossRef] [PubMed]
 
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