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Radiation and the risk of cardiovascular diseases in the low-dose range

Even at relatively low doses, ionising radiation increases the probability of developing cardiovascular diseases. This is indicated by the findings of an extensive metastudy in which the Federal Office for Radiation Protection also participated and which was published in the prestigious British Medical Journal. For example, these findings are relevant to occupational radiation protection or patients who are subject to an application of radiation.

Illustration of the human cardiovascular system Cardiovascular systemSource: peterschreiber.media/Stock.adobe.com

It has long been known that there is a greater risk of heart disease following radiotherapy. This relationship has been the subject of thorough scientific investigation, particularly in studies on radiotherapy following breast cancer or Hodgkin's lymphoma. Radiotherapy with a dose of several grays can result in considerable radiation doses in the region of the heart or other organs and tissues that play an essential role in the cardiovascular system.

In recent years, however, there have also been indications of increased risk in studies investigating a significantly lower radiation dose range of 500 milligrays (mGy) or less. Nevertheless, the scientific evidence of a relationship with cardiovascular diseases is still not particularly reliable in the range of moderate or low radiation doses, as this evidence originates from a relatively small number of stud-ies and the existing literature is somewhat contradictory.

The current systematic review and meta-analysis have now considerably strengthened the scientific evidence.

MethodShow / Hide

An international team of researchers sifted through more than 15,000 studies on the risk of cardio-vascular diseases following radiation exposure. After this process, 93 meaningful studies remained and were evaluated in a meta-analysis.

The examined studies covered wide-ranging forms of radiation exposure in various situations – primarily radiotherapy and occupational exposure to radiation, but also diagnostic radiology and environmental exposure.

As well as cardiovascular diseases, the examined subgroups included ischaemic heart disease (e.g. heart attacks), other forms of heart disease, cerebrovascular disease (strokes and other diseases of the blood vessels in the brain) and other cardiovascular diseases.

Results of the meta-analysisShow / Hide

The meta-analysis shows that risk increases with increasing radiation dose. The risk varies between the subgroups and is highest for cerebrovascular diseases such as stroke and other diseases affecting the blood vessels in the brain.

In the meta-analysis, the additional relative risk for all cardiovascular diseases combined is 11 % per gray. The risk of disease without exposure to radiation would increase:

  • by 1.1 % for 0.1 grays (100 milligrays)
  • by 11 % for 1 gray
  • by 22 % for 2 grays.

A significant increase in risk was also found at a maximum dose of less than 500 milligrays. This also applied to the subgroup of ischaemic heart diseases.

The meta-analysis also revealed significant differences between the results of different studies. However, these differences were less pronounced in high-quality studies and in studies in the rela-tively low dose range or at low dose rates.

There was a noticeably higher relative risk of ischaemic heart disease and all cardiovascular diseases combined per unit of radiation dose in the event of a low dose (under 500 milligrays) or a low dose rate (a prolonged dose over hours or years) compared with the risk at higher radiation doses or dose rates.

In the results of the meta-analysis, the additional absolute lifetime risk of dying from a cardiovascu-lar disease caused by radiation is moderately – albeit significantly – increased. This figure was between 2.3 % (England and Wales) and 3.6 % (Germany) per gray depending on the study and on the country in question, as well as on the different underlying mortality rates for cardiovascular diseases. In other words, for every 100 people exposed to a radiation dose of 1 gray, an additional 2 to 4 people would die of a disease of the cardiovascular system as a result of the radiation. Among these deaths, the dominant diseases are cerebrovascular diseases and ischaemic heart disease.

Overall, the results confirm the assumption of a causal relationship between cardiovascular diseas-es and high radiation doses. They also point to an increased risk even at lower radiation doses. However, there are still some uncertainties (e.g. differences in results between studies) and gaps in research (underlying biological mechanisms in the low-dose range, influence of lifestyle and medical factors etc. on radiation-induced cardiovascular disease risk).

Significance for radiation protection and medical radiation applications

Although the results of this meta-analysis show that the estimated additional absolute lifetime risk of dying of a radiation-induced cardiovascular disease is slightly lower than the estimated risk of dying of a radiation-induced cancer, it is of the same order of magnitude. If these estimates can actually be extrapolated to the low-dose range of 0 to 500 milligrays, this would have consequences for radiation protection because it could mean a doubling of the previously assumed extent of harm due to radiation (the "detriment") in the low-dose range.

In people with a high risk of cardiovascular disease, e.g. due to smoking, lack of exercise or additional conditions such as diabetes or hypertension, exposure to radiation could lead to a particularly pronounced increase in the additional absolute lifetime risk. Should these people receive large radiation doses during medical treatment, particular care should be taken to control other modifiable risk factors.

In the population as a whole, the estimated risks due to most radiation exposure situations is very low. Exceptions include, for example, radiotherapy for cancer or treatment using radionuclides.

Radiation doses of approximately 0.1 grays for the affected organs are used in radiotherapy for benign diseases or treatment with radionuclides, for example. Such doses are also possible in the event of multiple diagnostic procedures using high doses or interventional applications of X-rays.

Patient lying on CT scanner Computed tomographyComputed tomography examination Source: REB Images via Getty Images

A computed tomography (CT) scan typically leads to a heart dose of between 0.0005 and 0.015 grays. According to the findings of Little et al. (2023), a group of 10,000 people each exposed to 10 such scans might expect 0.2–13 additional ischaemic heart disease deaths over a lifetime.

In occupational radiation protection and for the general public, there are strict limit values for exposure to ionising radiation. In medical radiation protection, the protection of patients is governed by the principles of justification and optimisation of radiation applications. Justification means that unnecessary radiation exposure must be avoided and that the benefit and risk must be carefully weighed up. Any radiation application also requires optimisation, i.e. exposure should be limited to the lowest level that is necessary to obtain the relevant diagnostic information.

On the one hand, these results underline the need for additional radiation research in the low-dose range, for example into the underlying biological mechanisms of action. On the other hand, they demonstrate that strict compliance with the principles of radiation protection is indispensable in all areas of medicine.

Publication in British Medical Journal

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State of 2023.03.09

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