CT Scan Radiation Guide: Dose, Side Effects, Cancer Risk, and Safety Considerations

If you're curious or concerned about CT scan radiation, this article will help you understand the risks.

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If you are thinking about booking a CT scan (computed tomography scan) but are worried about the level of radiation used in the scan, we’re here to reassure you that a CT scan is a safe and standard medical procedure. Our guide answers any questions you may have about CT scans, from whether experts consider them a safe imaging technique to how many CT scans you can have.

Do CT scans use radiation?

Yes, CT scans use radiation to take clear and detailed images of the inside of your body. Let’s dig into what type of radiation they use compared to other scans and how much radiation is in a CT scan. 

What radiation do CT scans use?

CT scans use high-energy (ionising) radiation. They use higher doses of radiation than other diagnostic scans, such as X-rays. So, there is a small amount of risk that you are being exposed to radiation that could cause cancer in the future. However, it’s important to remember that ionising radiation surrounds us in everyday life. It’s present in the ground, in building materials in our homes and workplaces, and occurs naturally in many types of food, such as Brazil nuts and bananas. In the UK, the average person is exposed to around 2.7 millisieverts (mSv) of radiation each year.

How much radiation is in a CT scan?

Your CT scan radiation dose depends on the type of CT scan you have and how your technician carries out the scan. Some CT scans use more radiation than others because they take longer, increasing the exposure. The equipment used and how the rest of the body is protected during the scan can also affect exposure. However, the UK government sets strict guidelines on the amount of tradition used during scans. So you can be reassured that they are as safe as they can be.

How much radiation in a CT scan vs an X-ray scan?

It depends on what part of the body is being scanned. For example, a chest CT scan contains a radiation dose of around 6.6 mSv, while a chest X-ray has a radiation dose of around 0.014mSv. So, you can see that radiation from X-rays is much lower than radiation from CT scans. But remember that CT scans offer much more detailed images than X-rays, allowing clinicians to diagnose conditions faster and more accurately. 

What are the risks of CT scans?

CT scans use ionising radiation, which increases the risk of developing cancer later in life. The more radiation exposure from CT scans, the higher the cancer risk. That’s why clinicians weigh the benefits of having a CT scan against the CT scan radiation risk, especially for children and vulnerable patients, and why they use techniques to minimise unnecessary exposure. 

Is a CT scan safe?

CT scans carry some radiation risk that prevents them from being considered 100% safe. However, we know that they provide reliable and accurate diagnostic information, making them valuable tools in fighting disease and saving the lives of thousands of people every year.

If you’re wondering how many CT scans are safe to have, it’s hard to say, as it depends on many factors, including your age and your medical history. The more CT scans you have, the more risk there is of exposure to radiation that may cause cancer. That’s why a clinician will only recommend a CT scan if they think it’s the best way to help diagnose and treat a medical condition. 

What CT scan radiation side effects are there?

Apart from the small risk of cancer from radiation, complications and side effects from CT scans are rare. However, some people have an allergic reaction to the contrast medium (a dye that helps to show blood vessels and organs more clearly) that is injected or ingested before the scan. This can cause:

  • sweating

  • a rash 

  • itchy skin

  • feeling weak

  • difficulty breathing

How much does CT scan increase cancer risk?

Experts estimate that around 6 in 1,000 cancers in the UK are linked to the type of radiation that CT scans use. While studies have found an increased risk of cancer, the overall CT scan cancer risk is still considered to be low. Health experts believe the benefits of CT scans far outweigh the risks of radiation exposure. 

How to get rid of radiation after CT scan procedures

Try not to worry about radiation staying in your body after your CT scan. Any radiation will leave your body naturally within a few hours. You may want to drink extra fluids to help your body flush out the contrast medium, but other than that, there’s nothing you need to do. 

How soon after radiation can you have a CT scan?

If you are having radiotherapy treatment for cancer, your oncologist will usually recommend a follow-up CT scan between six and 12 weeks after your treatment has finished. 

If you need to have multiple scans and you’re worried about the risk of radiation, it’s worth bearing in mind that there is no limit to how many CT scans you can have because the risk is considered to be low. However, it's important that each scan is carefully considered and only done with a clinician's guidance, to ensure the benefits will outweigh any risks.

Severely ill patients may need multiple CT scans to get the correct diagnosis and treatment, which may help to save their lives. People with head injuries may need two or more CT scans to make sure there is no swelling or bleeding in the brain. People with a chronic condition, such as Crohn’s disease, may need regular scans to monitor and manage their condition. 

It’s for these reasons, and the fact that the risk of radiation is considered to be low, that there is no upper limit on how many CT scans you can have, and no one-size-fits-all recommendations on how far apart they should be.

Every CT scan booking we receive is carefully assessed by an experienced GP or radiologist, who will ensure it is the correct scan and is medically justified. You will receive a pre-scan consultation call with them to discuss the reasons for your scan and whether a CT scan is safe and appropriate.

What other CT scan disadvantages should I keep in mind?

Apart from the very small risk from radiation and a possible (although uncommon) risk of allergic reaction to the contrast medium, there are a couple of other things to be aware of:

  • People with claustrophobia or people who get anxious in confined spaces, may find one disadvantage of CT scans is the CT scanner itself. While the scanner is open, some people may feel uncomfortable passing through the doughnut-shaped gantry.

  • People with poor kidney function may be at risk of further kidney damage from the contrast medium used in CT scans. However, your technician will check your most recent blood tests before your scan to ensure your kidneys are working well, so the chance of any damage is low. 

At Scan.com, we understand that people booking CT scans may be worried about the risk of radiation. That’s why you can book a consultation with one of our expert clinicians, who can answer any questions you have about the scan before you book. They can also help reassure you that booking a CT scan has many benefits that far outweigh the risks of radiation, allowing you to get a swift diagnosis and treatment.


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Ionising radiation: dose comparisons. (2011). https://www.gov.uk/government/publications/ionising-radiation-dose-comparisons/ionising-radiation-dose-comparisons

I've had many CT scans. Should I be concerned? (2022). https://www.radiologyinfo.org/en/info/safety-hiw_08

Power et al. 2016. Computed tomography and patient risk: Facts, perceptions and uncertainties. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5183924/

Radiation risk from medical imaging. (2021). https://www.health.harvard.edu/cancer/radiation-risk-from-medical-imaging



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