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Medical imaging study shows risks

28 August 2009: Three-year US study highlights harmful effect of radiation exposure through medical imaging procedures.

 

The cumulative effect of low doses of radiation during medical imaging can be harmful, researchers say.

The three-year study, published in the New England Journal of Medicine, included over half a million adults. The researchers calculated the dose of ionising radiation from imaging procedures to which each patient was exposed.

The researchers compared these figures to the general population’s exposure and the exposure of healthcare professionals, such as radiologists. They excluded any procedures in which radiation was given as treatment, such as radiation therapy for breast cancer.

The estimated amount of radiation each person received was measured in millisieverts (mSV) of ionising radiation. Exposure to doses over 50mSV has been linked to an increased risk of developing cancer. Healthcare professionals adhere to guidelines which restrict radiation exposure levels of 100mSV every five years (20mSV each year), with a maximum of 50mSV in any one year.

Nearly seven out of 10 people in the study had at least one medical imaging procedure in the three year period. Most of the patients were exposed to only about 2.4mSV each year. About 20 ,in 1000 of the patients were exposed to between 20 and 50 mSV and two in 1000 received more than 50mSV in the study. This small but substantial group of people are at a much higher risk of cancer.

If this were reflective of the US population, it would mean four million Americans are exposed to high and very high doses of radiation through medical imaging procedures.

Having unnecessary imaging procedures may mean that the risks outweigh the benefits.

Bupa International medical director, Dr Sneh Khema said: “The use of medical imaging such as CT scans has increased in recent years in the US, which means more people are being exposed to radiation at levels higher than the average.

"The risk of exposure needs to be balanced against the clinical need for the test. People need to be aware of the risk and have any imaging procedures in an accredited healthcare setting.”
 

Key facts

Categories of radiation exposure in the study are as follows:

  • Low - less than 3mSV in a year which is equivalent to the background level from natural sources in the US.
  • Moderate - up to 20mSV in a year which is the five year average limit of exposure for healthcare professionals.
  • High - up to 50mSV in a year, which is the maximum limit for healthcare professionals.
  • Very high - more than 50mSV in a year.

Medical imaging procedures in the study included X-rays, fluoroscopy, computerised tomography (CT) scans and nuclear medicines scans.

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