How bad is CT radiation

Is a CT examination safe?

A CT examination is not safe for the human body due to the exposure to X-rays, but the benefits outweigh the risks if used correctly. Therefore, a doctor with specialist knowledge in radiation protection checks before each examination whether the use of X-rays makes sense in the respective case and provides the so-called “justifying indication”.Particular caution applies to children and pregnant patients.

In this article we deal with the question of the risks associated with a CT scan and whether it is safe for the human body.

How high is the additional cancer risk from a CT scan in adults?

This question is not that easy to answer, as the studies and data so far mainly come from survivors of the atomic bombs from Japan. The group of survivors (for whom data are available) with the lowest radiation exposure received a dose of approx. 5 - 20 mSv. During CT examinations, patients receive an average dose of approx. 1 - 10 mSv, whereby the dose of a CT examination depends on a large number of different factors (see below). It has been shown that the Japanese survivors had a small but increased risk of dying from cancer. However, since the victims of the atomic bombs were exposed to a slightly higher level of radiation, one has to extrapolate the range for lower doses. If one postulates a linear relationship (called the LNT model), one can assume as a rough estimate:

The following information is from a publication by the US Food and Drug Administration (FDA). The individual cancer risk can hardly be estimated because it depends, among other things, on the examined body region, the age and the sex of the person examined. In addition, the uncertainty described above exists in low doses, so that ultimately no definitive statements are possible.

A CT examination with an effective dose of 10 mSv increases according to the LNT model according to the FDA the likelihood of dying from radiation-induced cancer 1:2000. In the United States, the likelihood of death for the general population from cancer is about 400:2000 (corresponds to 1: 5). Thus, the natural risk of dying from cancer is significantly higher than the radiation-induced risk of CT. According to this model, instead of a probability of 400: 2000, a person has a statistical risk of 401: 2000 of dying from cancer with a 10 mSv CT scan. Thus, the additional risk of cancer in adults is relatively low and the benefits clearly outweigh the risks of a CT scan when used correctly.

When considering this, it should always be taken into account that the omission of a CT in the event of clinical suspicion of a certain disease can also be associated with high risks. For example, a tumor could be “overlooked” in a still curable stage.

Sample doses of typical examinations

The following data are for guidance only; the actual radiation dose of an examination can fluctuate very widely and depends on many different factors. These include the individual size of the examined region, the examination protocol (e.g. use of a low-dose CT) and, last but not least, the CT device itself.

How does X-ray radiation from a CT harm the body?

X-rays can damage the DNA in the cells of our body. Most of the DNA damage is repaired by the body's own repair mechanisms, but this does not always succeed. Then, depending on which area of ​​the DNA was damaged, there is an increased risk of developing cancer later in life. If the radiation damage occurs in the germ cells, there is an increased genetic risk. Direct radiation damage as known, for example, from the TV series Chernobyl (e.g. burns to the skin) does not occur with the radiation doses used as part of a CT.

How can I reduce the radiation exposure of a CT?

As a patient, you should ask your doctor whether a dose reduction is possible during the planned examination. You should also make sure that you are offered protective measures such as gonadal protection or protective goggles. If the same information can also be obtained through another type of examination (e.g. ultrasound, MRT), this should be preferred.

Is the use of X-ray contrast media safe?

Usually, non-ionic contrast media are used for intravenous use, which are generally very well tolerated. In exceptional cases, however, the body can react allergically to the contrast agent. Signs that indicate an allergic reaction are, for example, a new itching of the skin or a new shortness of breath. In this case you should consult your doctor immediately inform so that he can initiate appropriate treatment. By the way: It is quite normal that contrast media can make you warm; some patients report a metallic taste in the mouth or a slight urge to urinate.

Since X-ray contrast media contains iodine and our thyroid metabolizes iodine, it must not be used in people with known hyperthyroidism. However, if a CT examination is absolutely necessary in people with hyperthyroidism, the doctor may be able to inhibit the uptake and synthesis of thyroid hormones with medication.

X-ray contrast media containing iodine can be harmful to kidney function if the kidney is damaged. It is therefore necessary to carefully weigh the benefits and risks in patients with previously known renal impairment. The doctor can support your kidneys by supplying you with sufficient fluid (e.g. via the vein) before or after the examination, and should also discontinue kidney-damaging medication.

Contrast media, which must be drunk before some examinations, is usually very well tolerated. It is known, however, that this can have a slight laxative effect.

What other risks does a CT have?

Sometimes “probably benign” changes become apparent during a CT examination, which may then have to be clarified by means of further diagnostics. In many cases, this is associated with further risks. For example, a focus in the lungs could be described as likely benign. However, in order to safely rule out a malignant tumor, it is decided to puncture the tissue. This, in turn, is associated with higher risks because it is an invasive procedure in the body.

The psychological burden

Doctors generally underestimate the psychological stress that a CT scan can pose for patients. The examination is often accompanied by worries and fears, especially if there is a more serious illness. Perhaps to cheer it up, it should be said that many examinations only serve to rule out serious illnesses. An example of this is anemia, also known as anemia. There are numerous, very different causes for this. Since one of these causes is a tumor disease, a full tumor diagnosis is carried out in many people with anemia, although this is not the cause. And if there is an urgent suspicion of a certain disease, it is always better to discover it as early as possible. If you don't know exactly what is causing the symptoms, you can treat them badly.


In the vast majority of cases, the expected benefit of a CT examination clearly exceeds the risks, so that this should be carried out if the question arises. The assumed additional cancer risk is very low compared to the natural risk, although no definitive statements can be made here for the reasons mentioned above. It should also be borne in mind that failure to investigate can be associated with much greater risks.

How many CTs per year?

Is there a certain number of CT examinations per year that can be carried out without hesitation? There is no such number because even a single CT examination is associated with risks. Therefore: As few CT examinations as possible, as many as necessary. If several CT examinations are necessary in one year, these should also be carried out after a corresponding examination of the indications.

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