Answer to Question #7251 Submitted to "Ask the Experts"

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 Myoview. Myoview is a trade name for tetrofosmin. For the stress portion of the test (i.e., while walking on a treadmill), 25 millicuries (mCi) are administered and for the rest portion of the test, 9 mCi are administered.

For females administered those amounts of ^99mTc Myoview, the effective dose is estimated to be 777 millirem (or mrem—a unit for effective dose) for the stress portion of the test and 280 mrem for the rest portion of the test. Summing those values results in a total estimated effective dose of about 1,057 mrem. For males, the calculated effective dose would be 648 mrem for the 25 millicurie stress portion and 233 mrem for the 9 millicurie 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 300 mrem 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 400 mrem. 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 (1,057 mrem for women and 881 mrem 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 5,000-10,000 mrem (50-100 millisievert).