Radiology Examinations –
Weighing the radiation risk

When deciding whether to obtain a radiology examination, the potential benefit of the diagnostic information must be weighed against the risks of the study.  For many radiology exams, there is a very small increased risk of cancer due to x-ray exposure.

All of us are exposed to x-rays every day of our lives.  This exposure is due to external radiation from sunshine, cosmic rays and radioactive isotopes that are in the water and soil, and due to internal radiation from radioisotopes within our bodies. 

The dose we receive from x-ray examinations can be related to the time it would take to receive the same dose from natural background radiation.  A table of these values for some common x-ray studies appears below (See Figure 1).

Figure 1

As you can see, the doses from most exams are low and equivalent to short times of exposure to background radiation.  Even the highest value in the table (1.5 years) would be equal to 0.15 years or 1.8 months in other areas of the world where background radiation is 10 times greater. [See note 1.}

The risks of ionizing radiation are of greater concern to people (such as those with VHL) who get repeated CT examinations.  To put these risks into perspective, consider the following:  From population studies, it has been determined that 1 in 5 or 20% of us will eventually die from cancer due to non-radiation sources.  There is very little data available for risk estimates at the CT dose levels, and we do not know if there is a radiation dose threshold for cancer.  Very conservative risk estimates are obtained by 1) disregarding any threshold, and 2) linearly extrapolating cancer risks down to the CT dose levels from the risks observed at much greater dose levels for survivors of the WWII atomic bombs. According to those estimates, the additional risk of cancer from a CT exam of the abdomen is 0.02%.  Thus, if you had one CT scan of your abdomen every year for 30 years, your added risk of eventually dying from cancer due to x-rays would be 0.6%.  Your total risk of dying from cancer would be 20.6% compared with the population average of 20%.  In summary, even conservative estimates indicate the added risk of multiple CT scans of the abdomen is small and almost insignificant. 

There are several things you can do to further minimize your risk.  First, talk with your physician to make sure each examination is needed.  Second ask if the CT examination is being supervised by a board certified radiologist.  These physicians design the examination to use the least amount of radiation necessary.  Third, you may want to consider an examination that does not use ionizing radiation such as ultrasound or magnetic resonance imaging (MRI). Ultrasound does not usually provide the detail needed to examine the kidneys of VHL patients. MRI is more expensive, often less readily available and may require sedation for claustrophobic patients, but is as useful as CT in detecting small renal lesions.

In summary, x-ray examinations including CT are generally safe.  Any small risk is outweighed by the tremendous benefit of the diagnostic information that is obtained.

As printed in the VHL Family Forum 17:2, May 2009. For permission to reprint, please contact VHL Family Alliance, editor@vhl.org. Further information is available from the VHL Family Alliance, info@vhl.org.