Risk of Tumors or Cancer from Head CT Scans
The risk of cancer from head CT scans is small but real, with studies suggesting that cumulative doses of about 50-60 mGy might approximately triple the risk of leukemia and brain cancer in children, though the absolute risk remains low at approximately one excess case per 10,000 head CT scans over 10 years for children under 10 years of age. 1
Understanding Radiation Exposure from Head CT
- A typical head CT scan exposes patients to approximately 2-4 mSv of radiation, which is equivalent to about 100-200 chest x-rays 2
- The International Commission on Radiological Protection has reported that CT doses can approach or exceed levels shown to result in increased cancer risk 2
- X-rays have been officially classified as a "carcinogen" by multiple international health organizations, including the World Health Organization's International Agency for Research on Cancer 2
Cancer Risk Assessment
- The additional individual relative lifetime cancer mortality risk due to ionizing radiation with whole-body exposure at a low single dose is estimated at 5% per sievert 3
- For head CT scans, the risk is proportionally lower than whole-body exposure, but still present 3
- Children are at higher risk than adults because:
Evidence on Cancer Risk
Supporting Evidence for Cancer Risk
- A retrospective cohort study found a positive association between radiation dose from CT scans and leukemia (excess relative risk per mGy 0.036) and brain tumors (0.023) 1
- Patients receiving cumulative doses of at least 30 mGy had a relative risk of leukemia of 3.18, while those receiving 50-74 mGy had a relative risk of brain cancer of 2.82 1
- Approximately 0.4% of all cancers in the United States may be attributable to radiation from CT studies 2
Questioning Evidence for Cancer Risk
- A methodologic review of studies examining cancer risk from low-dose radiation found that 21 out of 25 higher-quality studies did not support cancer induction by low-dose radiation 4
- This review suggested that exposure to multiple CT scans with a cumulative dose up to 100 mSv (approximately 10 scans) does not increase cancer risk 4
Risk Factors That May Increase Cancer Susceptibility
- Family history of cancer may increase susceptibility to radiation-induced cancer 5
- An interaction between CT scans and family history of cancer has been observed, with the odds ratio for glioma being three times higher in those with a family history of cancer 5
Clinical Decision Making
- The clinical benefits of head CT should outweigh the small absolute risks 1
- Alternative procedures that do not involve ionizing radiation (such as MRI) should be considered when appropriate 1
- For children with mild traumatic brain injury, clinical decision rules like the PECARN rules can help identify children at very low risk for clinically important brain injury who can safely avoid CT scans 2
Risk Reduction Strategies
- Radiation doses from CT scans should be kept as low as reasonably achievable (ALARA principle) 2
- Technological advances in CT scanning have helped reduce radiation doses while maintaining diagnostic quality 2
- Targeted dose monitoring and analyses of dose data can help identify areas where improvement is necessary 3
- Standardized study descriptions and patient size descriptors can help track and minimize radiation exposure 2
Communication of Risk to Patients
- Risk communication about CT scans is often inconsistent, with most risks (65%) communicated using text rather than visual formats 2
- Visual formats may enhance comprehension of risk information without bias 2
- Patient decision aids can assist in the process of considering and weighing risks, but there is no consistent manner of communicating radiation risk to patients 2
While the risk of cancer from head CT scans exists, it must be balanced against the significant clinical benefits of this diagnostic tool. For each individual patient, the decision to perform a head CT should consider the clinical necessity, alternative imaging options, and patient-specific risk factors.