Screening for Lung Cancer with CT: Part II

This is the second installment of a two-part series on screening for lung cancer with CT. For Part I, which discusses who should be screened for lung cancer with CT, click here.

If you are considering undergoing a lung cancer screening CT, the following are some things to think about regarding the benefits and risks of CT screening.

What are the downsides of getting a screening CT?

There are two potential negative consequences of getting a screening CT. The first is radiation. This will be discussed below. The second potential downside is that the CT may prompt additional testing, and in some cases that testing is done to diagnose benign (not cancer) processes. For instance, a suspicious pulmonary nodule may be surgically removed only to find out that it wasn’t a cancer. There is some overlap in the appearances of cancer and benign processes, thus a CT scan can not be 100 percent sure that an abnormal finding represents cancer. When a suspicious abnormality is seen, however, further testing is necessary including PET scan, biopsy or surgery. This testing has some potential side effects.

Should I be worried about the radiation I get from a CT?

Medical radiation has been a hot topic in the news recently and has raised concerns about the possibility of radiation-induced cancers. UCSF is very aware of this concern and has adopted many different techniques for reducing radiation from CT scans including the development low-dose protocols and the purchase of special software specifically designed for radiation reduction.

Each person is exposed to radiation in his/her daily lives from the environment. The yearly dose that each person receives by this means is approximately 3 millisieverts (mSv). Millisieverts is a measure of the dose the whole body receives. In comparison, a standard chest CT imparts a dose of around 6 mSv (i.e. twice the yearly dose from the environment). It is estimated that the lifetime risk of developing a fatal cancer after receiving a dose of 10 mSv is 1 in 2000. Remember that, in general, 1 in 4 people will develop cancer in their lifetime. When considered in this context, the risk of developing a cancer from a CT scan only slightly increases the overall risk from baseline.

Some people who get a screening CT will need one or more follow-up CTs for lung nodules. Small lung nodules have a low likelihood of representing cancer and are typically followed for a period of 1-2 years to ensure they are not growing. These additional CTs are done using a low-dose technique that imparts a radiation dose of approximately 1/10th of a standard CT. Thus, these additional CTs only increase the total radiation from CT by a small amount.

I have a lung nodule. Should I be worried?

Lung nodules are very common and the vast majority of them are benign (not cancer).  Greater than 50 percent of our patients will have a lung nodule found on CT, and more than 97 percent of these nodules are benign. Any nodule has a possibility of representing cancer. The role of CT scan is to determine the likelihood that any nodule is benign or malignant based upon that nodule’s features. Features of a nodule that is likely benign include size < 2 cm, smooth borders and lack of growth over time. Nodules that are likely benign are typically followed with serial CT scans to make sure they are not growing. If they show no growth for a period of 1-2 years, they are considered to be benign and no further follow-up is required. If a nodule shows any suspicious features, some immediate action is generally warranted.

I have a suspicious lung nodule. What do I do next?

Patients with a suspicious lung nodule on CT scan should be referred to a specialist in either pulmonary medicine or thoracic surgery to manage the work-up of that nodule.  Suspicious features of a nodule include size >2 cm, irregular or spiculated borders and growth over time. The next step in the work-up of that nodule depends upon multiple factors. Options include PET scanning, CT guided lung biopsy and surgery. Which of these is performed will depend upon a variety of different factors including the CT appearance, smoking history, age, symptoms and presence of other diseases.

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