What is the maximum number of Computed Tomography (CT) scans considered excessive in terms of radiation exposure?

From the Guidelines

The cumulative lifetime dose of radiation from CT scans that might increase cancer risk is generally considered to be above 100 mSv, and individuals should follow the ALARA principle (As Low As Reasonably Achievable) when undergoing imaging studies. According to the study by Boone et al 1, there is evidence of adverse effects of radiation at higher doses, with an incremental increase in the incidence of various types of cancer compared with incidence of such cancers in the unexposed population at doses greater than 100 mSv. A typical CT scan delivers about 1-10 millisieverts (mSv) of radiation, with chest CTs on the lower end (5-7 mSv) and abdominal/pelvic scans on the higher end (8-10 mSv) 1.

Key Considerations

• The American College of Radiology white paper on radiation dose in medicine 1 highlights the importance of minimizing radiation exposure, especially for children, pregnant women, and young adults, who are more sensitive to radiation effects.
• The study by Boone et al 1 notes that advances in knowledge and technology have improved the ability to estimate radiation dose and risk, and to optimize CT examination protocols.
• The use of low-dose CT protocols and alternative imaging options like MRI or ultrasound can help reduce radiation exposure when possible.

Recommendations

• Individuals requiring multiple CT scans should discuss with their doctor about alternative imaging options, spacing out scans when possible, and using low-dose CT protocols.
• Medical professionals should follow the ALARA principle when ordering imaging studies, and consider the cumulative lifetime dose of radiation when making decisions about CT scans.
• Patients should be aware of the potential risks of radiation exposure from CT scans, and discuss any concerns with their doctor.

From the Research

CT Scan Radiation Risks

• The number of CT scans that are considered too much radiation is not explicitly stated, but studies have shown that high levels of radiation exposure from CT scans can increase the risk of cancer 2, 3, 4.
• A study published in JAMA internal medicine estimated that approximately 103,000 future cancers could result from CT examinations performed in 2023 in the United States 2.
• The same study found that the estimated radiation-induced cancer risks were higher in children and adolescents, but higher CT utilization in adults accounted for most (93,000; 90% UL, 86,900-99,600 [91%]) radiation-induced cancers 2.
• Another study published in The Surgical clinics of North America discussed the risks to patient safety, including radiation-induced malignancy, associated with CT imaging 3.

Comparison of Imaging Modalities

• A study published in Nihon rinsho. Japanese journal of clinical medicine compared the advantages and disadvantages of different imaging modalities, including CT, MRI, and ultrasound, and noted that CT is an objective and universal imaging method, but has a problem of radiation exposure 5.
• The study also noted that MRI has similar diagnostic accuracy and indication to CT, but with the advantage of not imparting ionizing radiation, and that ultrasound is a well-tolerated and radiation-free imaging method, but has limitations of inter/intra observer variability 5.

Trends in Medical Imaging

• A study published in JAMA analyzed trends in medical imaging in the United States and Ontario, Canada, from 2000 to 2016, and found that rates of CT and MRI use continued to increase among adults, but at a slower pace in more recent years 6.
• The study also found that among children, imaging rates continued to increase except for CT, which stabilized or declined in more recent periods 6.