Volume 12 Issue 6 - June 2014
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Low-Dose CT Screening for Patients at High Risk for Lung Cancer
  The United States Preventative Services Task Force (USPSTF) has issued a Grade B recommendation for low-dose CT screening for lung cancer in certain high-risk individuals who:
Are asymptomatic
Are between the ages of 55 and 80 years
Have a history of at least 30 “pack-years” of smoking
Are either current smokers or have quit in the past 15 years
Do not have co-morbidities that would prevent effective treatment for lung cancer

  Annual screening reduces mortality by 20% in this high-risk population

  Screening is not an alternative to quitting smoking

  Screening results are presented in a structured reporting system called Lung-RADS

Eligibility Criteria
Smoking Cessation
Screening Protocol
Risks of Screening
Reporting: Lung-RADS
Incidental Findings
Further Information

Table 1. A Eligibility Criteria

Asymptomatic adults

History of ≥30 "pack years" of smoking

Current smokers or those that have quit within past 15 years

Age 55–80 years

Ability and willingness to undergo curative treatment

Following the results of the National Lung Screening Trial (NLST) that showed 20% reduction in mortality following annual screening of heavy smokers with low-dose CT, the United States Preventative Services Task Force (USPSTF) issued a grade B recommendation for lung cancer screening in this population. Under the Affordable Care Act (ACA), private insurers must cover any procedure that receives a grade B recommendation from the USPSTF without co-pay. This policy is likely to take effect in January 2015. However, the ACA does not specify if Medicare must cover the procedure. In April 2014, the Medicare Evidence & Coverage Advisory Committee (MEDAC) panel voted against recommending Medicare coverage for lung cancer screening. This recommendation is not binding, and the Center for Medicaid and Medicare Services (CMS) is expected to issue a decision in February 2015.

The American College of Radiology (ACR) has issued guidelines for the performance of lung cancer screening procedures and standardized reporting using a Lung-RADS lexicon similar to BI-RADS for breast cancer screening.

The aim of this article is to provide information regarding the USPSTF eligibility criteria, the reporting algorithm and recommended management for each category of screening results. It includes links to the Radiology Order Entry system, the Mass General lung cancer screening website, and the American College of Radiology lung cancer screening reporting documents.

Figure 1. A 69-year-old heavy smoker evaluated with screening CT. An 8 mm calcified nodule in the right lung (arrow) is consistent with a granuloma: LungRADS 1. This is a benign finding and a negative screen. The patient is recommended to return for annual screening 12 months.

Figure 2. A 63-year-old man evaluated with screening CT. Initial screening demonstrates a 5 mm nodule (arrow) that is likely a benign finding: LungRADS 2. The patient was advised to return for annual screening in 12 months.

Eligibility Criteria
The US Preventive Services Task Force (USPSTF) recommends annual screening for lung cancer with low-dose CT in asymptomatic adults aged 55 to 80 years who have a history of at least 30 "pack years" of smoking and are current smokers or have quit within the past 15 years (Table 1).  A "pack year" is defined as smoking a pack of cigarettes a day for a year. Screening is not recommended for those with health problems that substantially limit life expectancy or who cannot or are unwilling to undergo curative treatment. Nor is it appropriate for people who have smoked less than 30 "pack years" or who are under 55 years of age because the risks of screening in these populations may be greater than the benefits.

Smoking Cessation
Screening for lung cancer does not substitute for smoking cessation. All patients undergoing or considering screening should be offered counseling or pharmacotherapy for smoking cessation, which is the most effective way to reduce the risk of lung cancer. Individuals who chose to be screened are likely aware of their risk from smoking and may show increased motivation to quit. Moreover, efforts to help individuals quit smoking increase the cost-effectiveness of screening for lung cancer.

Figure 3. A 70 year old female referred for screening. CT shows a mixed solid and ground glass 7 mm nodule, the solid portion measures 3 mm: LungRADS 3. Follow-up CT recommended in 6 months showed increase in the solid component. Fine needle aspiration showed atypical cells and wedge resection revealed adenocarcinoma.

Figure 4. A 73-year-old woman was evaluated with screening CT. A 10 mm nodule was seen in the right lower lobe, consistent with lung RADS 4a. A foliow-up low-dose CT at 3 months was recommended.

Screening Protocol
The protocol used for lung cancer screening is a low-dose multi-detector helical non-contrast CT scan, which is performed during a single breath hold. Screening scans are repeated annually until an abnormality is detected or the patient no longer fits the criteria for screening. All patients with significant positive findings are no longer considered to be in the screening program but receive further diagnostic tests.

Risks of Screening
Low-dose CT screening for lung cancer yields a large number of abnormalities suspicious for cancer, most of which are false positives. In the NLST, positive findings (nodules ≥4 mm in any diameter or other abnormalities that were suspicious for lung cancer) were detected in 24.2% of low-dose CT screening studies. Over 95% of these abnormalities were benign on further examination. Subsequent retrospective analysis of the results of another study, the International Early Lung Cancer Action Program, showed that increasing the threshold nodule size to 6 mm reduced the number of positive findings by half without compromising cancer detection. With the higher threshold, only 12% of screening subjects can expect to return for follow-up imaging studies. Approximately 6% will need further evaluation that may require referral to a multidisciplinary clinic comprised of thoracic radiologists, thoracic surgeons, oncologists, and pulmonologists.

The availability of prior chest CT studies at the time of reporting helps the radiologist assess the stability of positive findings and thus reduces the possible need for follow-up.

In the NLST, 4% percent of cancers developed during the interval between annual screenings. These findings indicate that some low-dose CT screening studies are false negatives. Screening may also increase patient anxiety, especially when positive findings appear cancerous.

The radiation dose of a low-dose CT scan is approximately one third that of a standard thoracic CT scan (Table 2). It is comparable to one half of the annual radiation dose due to background radiation at sea level.

Table 2. Average Radiation Doses at Mass General for Selected Examinations
Imaging Examination Radiation Dose
Screening mammography (4 views) 1.2 mSv
Low-dose CT for lung cancer screening 1.5 mSv
Average annual background radiation 3 mSv
Conventional chest CT 4 mSv
CT colonography (screening) 3-5 mSv

Reporting: Lung-RADS
The ACR has developed a reporting system for lung cancer screening called Lung-RADS, which is similar in structure to the BI-RADS system for breast cancer screening. It assigns numbers according to the likely severity of the findings and provides recommended actions for follow-up (Table 3).

When a lung abnormality is observed, a number of characteristics are important for further management including the size of the nodule, whether it is new or existent, whether it is solid or not, and the presence and pattern of calcification. The Lung-RADS system categorizes these findings following precise descriptions to rank cancer risk. The ACR estimates that 90% of screening subjects will fall into Category 1 or 2 and either have no nodules or have those with a very low likelihood of developing cancer (Figures 1 and 2). An estimated 5% of screening subjects will have Category 3 findings that indicate a low (1–2%) likelihood of malignancy (Figure 3). In these cases, a follow-up low-dose CT screening study is recommended after six months. Approximately 4% will be assigned to Category 4, which is divided into two subgroups to account for a higher and lower likelihood of cancer. Patients with findings in Category 4A will be asked to return for a follow-up low-dose CT study in three months or in some cases may be recommended for a PET/CT scan (Figure 4). Those patients who have findings with the highest likelihood of malignancy are assigned to Category 4B. For these patients, follow up depends on the decisions of a collaborative team of radiologists, oncologists, and thoracic surgeons, who may opt for a chest CT with or without contrast, PET/CT, or biopsy (Figure 5) Note that nodule management for this group of patients differs from the published Fleischner guidelines and our institutional nodule management algorithm, which will remain in place for non-screening patients.

Table 3. Summary of the Lung-RADS Reporting System

Category Descriptor

Primary Category Management


- 0

Additional lung cancer screening

CT images and/or comparison to prior chest CT examinations is needed


No nodules and/or definitely benign nodules 1 Continue annual screening with low-dose CT in 12 months

Benign appearance
or behavior

Nodules with a very low likelihood of becoming a clinically active cancer due to size or lack of growth 2

Probably benign

Probably benign finding(s) with short-term follow up suggested; includes nodules with a low likelihood of becoming a clinically active cancer 3 Low-dose CT in 6 months


Findings for which additional diagnostic testing and/or tissue sampling is recommended 4A

Low-dose CT in 3 months

PET/CT may be used in cases of a ≥ 8 mm solid component


Chest CT with or without contrast

PET/CT and/or tissue sampling depending on the probability of malignancy and co-morbidities

PET/CT may be used in cases of a ≥ 8 mm solid component

*Significant - other - S -
*Prior lung cancer - C -
*Significant - other findings not related to cancer are indicated by the letter S while the letter C denotes prior lung cancer. These letters are used as modifiers to the primary categories 1–4.
Detailed version of the Lung-RADS reporting system can be found at American College of Radiology website.

Incidental Findings
In NLST, causes of death other than lung cancer included cardiovascular disease (Figure 6), respiratory disease, and other cancers. While the presence of low-attenuation lesions in the liver, kidneys, and thyroid are of uncertain significance, detection of coronary artery calcification and emphysema can change the management of the patient. Treatment of these diseases can improve outcomes.

Figure 5. A 58-year-old asymptomatic woman evaluated with screening CT. A 2.2 cm spiculated nodule in the middle lobe is highly suspicious for lung cancer: LungRADS 4b. The patient underwent CT-guided lung biopsy that confirmed adenocarcinoma and the patient was referred for surgical management.

Figure 6. Incidental finding in 73-year-old woman undergoing screening CT. There is heavy coronary artery calcification noted, which is a predictor for cardiovascular disease. No lung nodule was present and the study was categorized as Lung-RADS 1S.

Lung cancer screening is offered at the Mass General Imaging facilities in Chelsea and Waltham for a fee of $350 if it is not covered by insurance. Patients must be referred for screening by their doctors. Appointments can be made through ROE (inside Partners network) or ROE Portal (outside Partners network), or by calling 617-724-XRAY (9729).

Every effort should be made to obtain prior chest CT studies. At Mass General, studies performed elsewhere can be loaded onto the hospital PACS system through lifeImage prior to a screening examination. For assistance with lifeImage, please contact out Imaging Service Center at 617-726-1798 or visit this website.

The Massachusetts General Hospital Tobacco Treatment Service conducts smoking cessation consultations for in-patients. The Massachusetts Smokers' Helpline, at 1-800-QUIT-NOW (1-800-784-8669), provides confidential telephone information, referral, and counseling at no charge to smokers and other tobacco users who want to quit.

Further Information
For further information on low-dose CT screening for lung cancer, please visit massgeneralimaging.org/lungscreening or contact Amita Sharma, MD, or Jo-Anne Shepard, MD, Thoracic Radiology, Massachusetts General Hospital, at 617-724-4254.

We would like to thank Amita Sharma, MD, Jo-Anne Shepard, MD, and Inga Lennes, MD, Thoracic Oncology, Massachusetts General Hospital, for their assistance and advice on this issue.


Aberle DR, et al. (2011). Reduced lung-cancer mortality with low-dose computed tomographic screening. N Engl J Med 365:395-409

Godtfredsen NS, et al. (2005). Effect of smoking reduction on lung cancer risk. Jama 294:1505-10

Goulart BH, et al. (2012). Lung cancer screening with low-dose computed tomography: costs, national expenditures, and cost-effectiveness. J Natl Compr Canc Netw 10:267-75

Henschke CI, et al. (2013). Definition of a positive test result in computed tomography screening for lung cancer: a cohort study. Ann Intern Med 158:246-52

American College of Radiology (2014) Lung CT Screening Reporting and Data System (Lung-RADS)

Moyer VA (2014). Screening for lung cancer: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med 160:330-8

©2014 MGH Department of Radiology

Janet Cochrane Miller, D. Phil., Author
Raul N. Uppot, Editor



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