Does a Computed Tomography (CT) scan increase the risk of developing cancer?

From the Guidelines

CT scans do expose patients to ionizing radiation, which slightly increases the risk of developing cancer over time, with an estimated risk of less than 1 in 1,000 from a single scan. The amount of radiation varies by scan type, with chest, abdominal, and pelvic CTs delivering higher doses than head scans [ 1 ]. For context, a chest CT delivers approximately 7 millisieverts of radiation, equivalent to about 2 years of natural background radiation. The cancer risk is higher for children and young adults due to their developing tissues and longer life expectancy [ 1 ]. Despite this small risk, CT scans provide valuable diagnostic information that often outweighs the potential harm. Doctors follow the ALARA principle (As Low As Reasonably Achievable) when ordering imaging studies, considering alternatives like ultrasound or MRI when appropriate [ 1 ].

Key Considerations

• The risk of radiation-induced malignancy from CT scans is small but real, with approximately 0.4% of all cancers in the United States potentially attributable to the radiation from CT studies [ 1 ].
• Advances in technology and medical physics have helped to reduce the dose of radiation that patients receive from tests such as CT scans [ 1 ].
• The radiation exposure of a CT scan is still equivalent to about 100 to 200 chest x-rays, depending on a patient’s size and imaging needs [ 1 ].
• There are also risks associated with the intravenous contrast dye used to increase the diagnostic yield of CT scans, including allergies and severe reactions [ 1 ].

Clinical Implications

• If you need a CT scan for medical reasons, the immediate benefit of accurate diagnosis and treatment typically far outweighs the minimal long-term cancer risk [ 1 ].
• Doctors should consider the ALARA principle and alternative imaging modalities when ordering CT scans to minimize radiation exposure [ 1 ].
• Patients should be informed of the potential risks and benefits of CT scans, including the small risk of radiation-induced cancer, to make informed decisions about their care [ 1 ].

From the Research

Computed Tomography (CT) Scan and Cancer Risk

• The relationship between CT scans and cancer risk has been a topic of debate in the medical field, with some studies suggesting a potential link between the two 2, 3, 4.
• Data extrapolated from atomic bomb survivors and other populations exposed to low-dose ionizing radiation suggest that CT scan-associated radiation may increase an individual's lifetime risk of developing cancer 2.
• However, the risk of cancer from CT scan radiation is still a topic of discussion, and some studies have found that the presumed overall risk of radiation-induced cancer continues to be low 3.
• The communication of the radiation risk from CT in relation to its clinical benefit is important, and most authorities now conclude that there is enough evidence to link future cancers to the radiation exposure from a single CT scan in childhood 4.

Radiation Exposure and Cancer Risk

• The risk of cancer from CT scan radiation is related to the dose of radiation exposure, with higher doses increasing the risk of cancer 3, 5.
• However, the small theoretical increase in risk of cancer incidence must be considered in the context of the clinical benefit derived from a medically indicated CT and the likelihood of cancer occurrence in the general population 5.
• Elimination of unnecessary imaging is the most important method to reduce imaging-related radiation, and technical aspects of medically justified imaging should also be optimized to minimize the dose of radiation 5.

CT Scans and Cancer Screening

• The use of CT for population-based cancer screening continues to be explored for common malignancies such as lung cancer and colorectal cancer 6.
• The available data suggest a small but real risk of radiation-induced malignancy from CT that could become significant at the population level with widespread use of CT-based screening 6.
• However, a growing body of literature suggests that the benefits of CT screening for lung cancer in high-risk patients and CT colonography for colorectal cancer may significantly outweigh the radiation risk 6.