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Answer to Question #7251 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:

Q

I am to have a nuclear stress test that is supposed to be the most up-to-date test and machine to date. I am confused about the amount of radiation on the tables with multiple levels. All I really know is that it is a nuclear stress test that takes three to four hours to complete and I will walk the treadmill and rest. Can you give me an idea of the amount of radiation exposure with this information? I am 33 years old and have had many radiation tests in the last 10 years.
 

A

Without specific details on the radiopharmaceutical and amount utilized, the question can be answered, but with a several assumptions. Our medical center performs cardiac stress/rest tests using a radiopharmaceutical called 99mTc (technetium-99m) Myoview. Myoview is a trade name for tetrofosmin. For the stress portion of the test (i.e., while walking on a treadmill), 930 MBq are administered and for the rest portion of the test, 333 MBq are administered.

For females administered those amounts of 99mTc Myoview, the effective dose is estimated to be 7.77 millisievert (mSv) for the stress portion of the test and 2.8 mSv for the rest portion of the test. Summing those values results in a total estimated effective dose of about 10.57 mSv. For males, the calculated effective dose would be 6.48 mSv for the stress portion and 2.33 mSv for the rest portion. These calculated values would of course be different if other radiopharmaceuticals (e.g., 201Tl) and/or different amounts are utilized. The difference for men and women is that the women's dose includes the dose to the ovaries and uterus versus the men's dose to the testicles.

To put that total effective dose in perspective—we all receive an effective dose equivalent of about 3 mSv each year from what is called background radiation. This background radiation includes radon, cosmic rays, radiation from natural radioactivity in the earth, etc. If one lives at higher elevations (e.g., Denver, Colorado), the annual background radiation level is estimated to be around 4 mSv. While there are some technical differences between the terms effective dose and effective dose equivalent, they can be considered about the same for comparison purposes.

Thus, the effective dose (10.57 mSv for women and 8.81 mSv for men) from the stress/rest test example above would be equivalent to what one would receive from about 3.5 years for women and 3 years for men of background radiation for the average member of the U.S. population or about 2.6 years of background radiation for a woman living in the Denver area, two years worth for a man living in Denver.

Even though we assume that there may be a higher risk of cancer/leukemia from any radiation exposure, there is no human data that specifically indicates there is any statistically significant risk from radiation dose equivalents of this magnitude.1 For warranted medical procedures with either x rays or radiopharmaceuticals, the benefit of the information obtained from the procedure significantly outweighs the risk from the radiation dose equivalent.

Mack L. Richard, MS, CHP


1 As noted in the Health Physics Society Position Statement on "Radiation Risk in Perspective," there is no demonstrated health effect for radiation exposures below 50-100 millisievert.
 

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 21 February 2008. 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.
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