Answer to Question #6774 Submitted to "Ask the Experts"

I'm sure that it was quite disturbing for you to be told after 45 minutes that you should not be there. Hospital personnel are trained to keep radiation exposure to family members as low as possible, so that is why the person told you that you should move. Most hospitals do not let patients have company sit with them prior to a PET scan. It is also important for the patient to rest so that the radiopharmaceutical can go to where it needs to go. If the patient moves around, it can accumulate in body parts that are not important to the scan.

I took a radiation exposure reading of a patient who had received an injection of 10 millicuries of the PET radiopharmaceutical. At three feet, I had a reading of 5 mR/hr (milliroentgen/hour). So if you were sitting three feet away for one hour, your radiation exposure would have been 5 mR. Since you were at two feet for 45 minutes, your estimated exposure would have been around 8 mR. It is not a linear calculation, but since you were closer, the dose was higher. The amount of radiation exposure that you received would not be a concern to me if I had been sitting there.

As points of reference, I can give you some examples of radiation doses that people receive from natural background radiation. Natural background radiation includes cosmic radiation, material in the earth, and naturally occurring material in food and water. If you lived in Denver, your dose from natural background radiation is approximately 3 millirem in one day. The radiation dose from a coast-to-coast airplane flight is about 4-5 millirem. So the dose from your time spent close to your mother is similar to the exposure from living in Denver on vacation for three days or from two cross-country airplane flights. An 8 mR exposure is considered equivalent to an 8 millirem dose. Even if your mother had a higher dose, it was probably not more than double that dose. And I would guess that most people would not avoid a week's vacation in Denver because of the increased radiation exposure.

Regarding your second question, I cannot think of a way for the dose to be amplified. Your mother's body was absorbing the dose, so you could say that her body was shielding you from radiation exposure. There is no way to increase dose unless you add another injection of radioactive material.

I hope this answers your questions and helps put your radiation exposure into perspective.

Marcia Hartman, MS
 

Editor's Note: The information on the natural background exposure in Denver is from the Institute for Science and International Security Web site. The value is listed as 11.8 mSv/yr (millisievert/year), which equals 1,180 millirem annual exposure from radon, cosmic, and terrestrial radiation, food, and water.