Answer to Question #7917 Submitted to "Ask the Experts"

Category: Nuclear Medicine Patient Issues — Diagnostic Nuclear Medicine

The following question was answered by an expert in the appropriate field:

I have been very sick this year and have had the following tests within a 10-month period: three abdominal/pelvis CT scans, one brain CT scan, one sinus CT scan, one heart CT angiography scan, and one nuclear medicine white blood cell scan. I am very worried about overexposure and I am having trouble finding out what safe limits are.

The summed effective dose for the seven exams you listed, received over a period of 10 months, is approximately 66 millisievert (mSv). In comparison, the annual effective dose limit for occupational radiation workers is 50 mSv/year and you receive an effective dose of approximately 3 mSv/year from natural radiation sources like the sun and naturally occurring radioactive materials.

In medical practice, there is no annual patient dose limit because the immediate medical benefit of the diagnostic information far outweighs the small risks from the radiation dose resulting from the test. If you are sick now, diagnosing the condition and addressing it immediately is the right choice.

An effective dose of 66 mSv is so small that it would be difficult to scientifically measure the increased risk or there may be no risk. In human populations, we can only reliably measure an increased risk at effective doses greater than 100 mSv. At doses lower than 100 mSv, we can only estimate the risk, because it's too small to measure directly. However, the benefits of diagnostic scans are easily measured and result in lives saved and improved health for many.

Some recently published papers have expressed concern about the increased use of diagnostic exams that use radiation sources. These papers have received a good amount of publicity in the press and have a point in that medical users of radiation have a responsibility to ensure that the radiation exams are necessary, minimize the doses needed to produce the information, and are not duplicating prior exams.

However, these papers only address the small risks from the radiation and ignore the immediate benefits these diagnostic exams provide to patients. As the saying goes, "There's no free lunch." When we are suffering from an illness, should we avoid a small theoretical risk while ignoring the immediate problem at hand? In most cases, the immediate problem needs to be addressed now and the alternatives to diagnostic radiation scans are either less effective or more risky.

The benefits of medical radiation exposures were recently addressed in response to these papers by the Health Physics Society and the American Association of Physicists in Medicine, and I would recommend the following articles for your consideration:

In summary, I would like to reassure you that you were not "overexposed" to radiation. Your dose was too small to cause any acute radiation effect. I hope that you have enjoyed the immediate benefits of the diagnostic information in exchange for a long-term risk that is too small to measure.

Mike Bohan
Radiation Safety Officer

Answer posted on 13 February 2009. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.