A CT scan generally exposes a person to a significantly higher dose of ionizing radiation than what they receive from everyday background radiation, but the risk depends on the amount and frequency of exposure. Everyday background radiation comes from natural sources like cosmic rays, soil, and radon gas, and it is relatively low and constant. In contrast, a single CT scan delivers a concentrated dose of radiation to a specific part of the body, which can be many times higher than the annual background radiation dose.
To put it in perspective, the average person is exposed to about 3 millisieverts (mSv) of background radiation per year from natural sources. A typical CT scan can deliver anywhere from about 2 to 20 mSv depending on the type of scan and the body part being imaged. For example, a chest CT might expose a patient to around 7 mSv, which is roughly equivalent to two years of natural background radiation. More extensive scans, like an abdominal and pelvic CT, can be even higher.
This difference in radiation dose is important because ionizing radiation has the potential to damage cells and DNA, which can increase the risk of cancer over time. While the risk from a single CT scan is generally low, it is not zero. Studies have shown that even low doses of radiation, such as those from medical imaging, can slightly increase the risk of cancer, especially with repeated exposures. Children and young adults are more sensitive to radiation, so the risks are higher for them compared to older adults.
The scientific community continues to study the exact risks associated with low-dose radiation from CT scans. Some research indicates that doses as low as 10 mGy (milligray, a unit related to mSv) can elevate cancer risk, and since many CT scans deliver doses in this range, the concern is valid. However, the risk must be balanced against the benefits of the scan, which often provides critical diagnostic information that can save lives or guide important treatment decisions.
In comparison, background radiation is a constant, low-level exposure that our bodies have adapted to over millions of years. It is generally considered safe at these low levels, although certain populations exposed to higher natural background radiation have been studied to understand long-term effects. The radiation from a CT scan is a short, intense burst, which is why it carries a different risk profile.
Medical professionals aim to minimize radiation exposure by using the lowest dose necessary to achieve clear images and by considering alternative imaging methods like MRI or ultrasound, which do not use ionizing radiation. Guidelines and quality measures are in place to avoid unnecessary scans or excessive radiation doses during CT imaging.
In summary, a CT scan exposes you to more radiation than you receive from natural background sources in a short time, and this increased dose carries a small but measurable risk of cancer, especially with repeated scans or in sensitive populations. However, the diagnostic benefits often outweigh these risks, and ongoing research and technology improvements continue to reduce radiation doses and improve safety.