Radiology Rounds - May 2011 - Mass General Imaging Global Health Programs
Volume 9 Issue 9 - September 2011
                       
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CT Screening for Lung Cancer for High Risk Patients
     
  The recently published National Lung Cancer Screening Trial (NLST) showed that low-dose CT screening for lung cancer reduces mortality in high-risk patients

  However, screening results in a high rate of false-positive findings that require follow-up

  There are currently no national society guidelines regarding who should be screened

  Mass General Imaging offers CT screening for lung cancer, recommended in patients who meet the criteria used in the NLST

  CT screening for lung cancer is not covered by insurance

     


   
Table 1. Selection Criteria for CT Screening for Lung Cancer
Current and former smokers with a history of 30 pack-years of smoking*:
-

Former smokers must have quit within past 15 years

55-74 years of age

No history of cancer within the past 5 years†

*A pack year equals the number of packs smoked per day multiplied by the number of years the patient smoked
Patients with a history of cancer may qualify for routine CT studies

Lung cancer is the leading cause of cancer-related deaths. There is considerable evidence that if lung cancer is detected early, mortality is reduced. The National Lung Cancer Screening Trial (NLST), published in June 2011, demonstrated that lung cancer mortality in a high-risk population can be reduced by low-dose CT screening. Unlike prior studies that failed to show a benefit from screening, the NLST was a large prospective randomized clinical trial. The 53,454 participants (aged 55 to 74 years) all had a history of cigarette smoking of at least 30 pack-years and, if former smokers, had quit within the last 15 years. None had a history of cancer of any kind.

Individuals in the NLST trial were randomized to screening by low-dose CT or by radiography. Three exams were given: the first at baseline, the second one year after baseline and the third two years after baseline. The incidence of lung cancers was 645 cases per 100,000 person-years (1060 cancers) in the CT group and 572 cases per 100,000 person-years (941 cancers) in the radiography group (rate ratio, 1.13; 95% confidence interval, 1.03-1.23). The relative reduction in mortality (compared with radiography) from lung cancer with low-dose CT screening was 20%. The death rate from any cause in the CT screening group was reduced by 6.7%, compared to the radiography group. One death from lung cancer was prevented per 320 participants in screening.

Approximately 40% of the participants in the NLST had positive findings of small indeterminate pulmonary nodules considered suspicious for lung cancer in at least one of the three screening tests. These required diagnostic follow-up, mostly with further imaging and, in some cases, invasive procedures. Of these initial findings, 96.4% of the findings in the low-dose CT group were false positives. The rate of at least one complication during follow-up of the CT group was 1.4%. The rate of major complication was 0.06% in the false positive group and 11.2% in those with lung cancer. Of the cancers detected, most were adenocarcinomas, many of which were detected at stage I or stage II.  Small cell lung cancers were, in general, not detected at early stages.

Figure 1. (A) Chest CT of a 70 year-old patient, a heavy smoker, revealed a 4 mm nodule (arrow) in right upper lobe. (B) Follow-up CT one year later shows the small nodule, increased in size. It was biopsied and then resected, revealing adenocarcinoma, papillary type.
Figure 1. (A) Chest CT of a 70 year-old patient, a heavy smoker, revealed a 4 mm nodule (arrow) in right upper lobe. (B) Follow-up CT one year later shows the small nodule, increased in size. It was biopsied and then resected, revealing adenocarcinoma, papillary type.


Indications for Lung Cancer Screening at Mass General Imaging
Although the results of the NLST were positive, it is not clear how they translate to general clinical practice.  National medical societies such as the American Cancer Society are developing guidelines for screening programs, but none are currently available.

Mass General Imaging now offers low-dose CT lung cancer screening. In the absence of national medical society guidelines, Mass General Imaging recommends using the same inclusion criteria used by the NLST, that is, patients aged 55 to 74 years who are current or former smokers with a history of 30 pack-years of smoking and who have no history of cancer within the past 5 years (Table 1).

Lung cancer screening CT studies must be ordered by a physician. The screening study is a non-contrast CT performed with a very low dose protocol with a radiation exposure of approximately 1.5 mSv. This is lower than that for a routine chest CT (about 3 mSv) and a fraction of some other CT scans. In comparison, typical annual background radiation from natural sources is 3.0 mSv in North America. The average radiation dose received from CT screening exams is likely to continue to decrease over time and may gradually become a less important issue.

Figure 2. Lung cancer detected by screening CT in a heavy smoker. (A) Low-dose screening CT shows a spiculated nodule in the right upper lobe (arrow). (B) FDG-PET confirmed (arrow) likelihood of cancer. The patient underwent biopsy and the nodule was found to be an adenocarcinoma.
Figure 2. Lung cancer detected by screening CT in a heavy smoker. (A) Low-dose screening CT shows a spiculated nodule in the right upper lobe (arrow). (B) FDG-PET confirmed (arrow) likelihood of cancer. The patient underwent biopsy and the nodule was found to be an adenocarcinoma.


Follow-up of Positive Findings
On screening CT, the finding of a small non-calcified pulmonary nodule (Figures 1 and 2) is regarded as suspicious for cancer and will require further evaluation. The current algorithm incorporating Fleischner Society guidelines for the evaluation of pulmonary nodules detected by CT imaging is shown in Figure 3. By definition, nodules found during CT screening for lung cancer fall in the category of nodules in patients with "No History of Cancer within the Past Five Years" and are in the "High Risk Category" highlighted in yellow in Figure 3. The selection of follow-up diagnostic imaging or procedure(s) and their timing depends on the size of the lesion and its morphologic characteristics, particularly if it has a "ground glass" or solid appearance.

Risk and Benefits
As the NLST trial demonstrated, screening does not prevent all deaths from lung cancer; it reduced the death rate by 20%. Screening also yields a high rate of false positive findings, some of which are incidental findings outside the lung. Although the vast majority of these findings are benign, they may result in unnecessary anxiety during follow-up care. For most patients, follow-up for indeterminate pulmonary nodules will be limited to non-invasive imaging, including CT or PET/CT, which will lead to additional cost and radiation exposure. Larger nodules may require needle biopsy, bronchoscopy, or video assisted thoracoscopic surgery (VATS) to establish the diagnosis and may lead to potential complications. The potential for adverse events associated with positive findings must be discussed with patients considering screening. While there is no insurance coverage for the screening CT scan, insurance should cover follow-up care for patients with positive findings. It should be emphasized that screening is not an alternative to smoking cessation, and active smokers undergoing screening CT should enter a smoking cessation program.

Figure 3.
Figure 3. Algorithm for follow-up of pulmonary nodules. (Download PDF)


Scheduling
Appointments for low-dose CT for lung cancer screening can be scheduled by calling 617-724-9729 or through the Radiology Order Entry system, http://mghroe/. The screenings are performed at the Mass General Imaging Centers in Chelsea, Waltham, and Worcester only and are not covered by insurance. The patient will be charged $350, due at the time of the screening examination. It is important that a responsible health care provider manage follow-up care for patients with a positive finding. Follow-up imaging examinations, which are covered by insurance, can be performed at the Mass General imaging centers or the main hospital campus.

A consultation for PNAB of the lung can be requested by calling Thoracic Imaging and Intervention at 617-724-4254 or by faxing a Thoracic Biopsy Approval form (PDF) to 617-724-0046, available on the Mass General Imaging website.

The Mass General Tobacco Treatment Service provides counseling on tobacco cessation. For more information, please call 617-726-7443.


Further Information
For more information about imaging CT screening for lung cancer, please contact Jo-Anne O. Shepard, MD, Director of Thoracic Imaging, Mass General Hospital, at 617-724-4256.

We would like to thank Theresa McLoud, MD, and Matthew Gilman, MD, Mass General Imaging, and Sue Loomis, Radiology Educational Media Services (REMS) for their assistance and advice for this issue.




References

Aberle DR, Berg CD, Black WC, Church TR, et al. (2011) The National Lung Screening Trial: overview and study design. Radiology 258: 243-253.

Henschke CI, Yankelevitz DF, Naidich DP, McCauley DI, et al. (2004). CT screening for lung cancer: suspiciousness of nodules according to size on baseline scans. Radiology 231: 164-168.

MacMahon H, Austin JH, Gamsu G, Herold CJ, et al. (2005). Guidelines for management of small pulmonary nodules detected on CT scans: a statement from the Fleischner Society. Radiology 237: 395-400.

The National Lung Screening Trial Research Team (2011). Reduced Lung-Cancer Mortality with Low-Dose Computed Tomographic Screening. N Engl J Med 2011;365:395-409.




©2011 MGH Department of Radiology

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