Answer to Question #4043 Submitted to "Ask the Experts"

An inexperienced x-ray technician in a disability screening facility took between 15 and 30 x rays of me, trying to adjust the settings on a machine too small for a person of my size. I consulted with the county radiation control unit and they investigated and informed me that the state physicist concluded I received a minimum of 5,025 mR. Neither they nor my doctor will discuss what, if anything, this means except to say "that's a lot of radiation." They act "funny" when I bring it up and change the subject quickly. My doctor did decide to check my blood and said "as of right now, your blood is close to normal."

How much radiation is 5,025-10,050 mR and what did it do to me? I can't get a straight answer from anyone. I would appreciate any explanation/approximation you can offer. I just need some general information. Can you help me?

Interesting question, thanks for asking. Let me start with a couple of things, then give some other typical radiation doses for comparison, and finish with possible risks.

The unit of radiation exposure you provided in your question is given in terms of mR or milliRoentgen. This is a unit typically used for the entrance skin exposure—not the actual amount received by the organs in the x-ray field or the amount we use to determine risk from radiation exposure. The dose received by the organs is typically less than the exposure to the skin where the x rays enter (so the risk is less; effective dose is usually reported in a radiation unit called millirem or mrem). I also point this out because, for instance, radiation exposure of your arm is going to have little if any risk associated with it; so exposure to your arm cannot really be added to an exposure of your abdomen. In any event, I have included a table listing various skin exposures and effective doses for some common diagnostic x-ray exams so you can see this for yourself (Wall 1997).

Single Radiographs	Skin Exposure, mR	Effective Dose, mrem
Chest (PA)	15	2
Chest (lateral)	40	4
Thoracic spine (AP)	200	40
Thoracic spine (lateral)	500	30
Lumbar spine (AP)	250	70
Lumbar spine (lateral)	600	30
Abdomen (AP)	250	70
Pelvis (AP)	250	70
CT chest	3,000-4,000	800
CT pelvis	3,000-5,000	1,000
CT abdomen	3,000-5,000	1,000

Another comparison that might be useful is the regulatory occupational dose limit for employees who take the x rays or who are exposed to radiation for other reasons because of their job. The regulatory occupational limit is 5,000 mrem per year.

As for the risk of radiation doses, the risk for lifetime fatal cancer due to radiation exposure is estimated at 5 per million per 1,000 mrem (NCRP 1993). This means if one million people were exposed to 1,000 mrem of radiation over their lifetime, five of those million would develop a fatal cancer. The general lifetime fatal cancer risk is about 200,000 per million (about one in five). That means, without additional radiation exposure, we each have a one in five risk of getting cancer. Adding the risk from 10,000 mrem of radiation exposure to the general risk, the total calculated fatal cancer risk would go from 200,000 per million to about 200,050 per million.

This is only a calculation and it is based on statistics obtained from people receiving very high amounts of radiation exposure. According to Dr. Eric Hall, a radiobiologist and professor of radiation oncology and radiology at Columbia University, 5,000 mrem/y is conservatively the lowest dose rate where there is any evidence of cancer risk (Hall 1984).

I hope this information is useful for you to put the radiation level you received into perspective.

Kelly Classic
Certified Medical Health Physicist

References
Wall BF, Hart D. Revised radiation doses for typical x-ray examinations. The British Journal of Radiology 70:437-439; 1997. (5,000 patient dose measurements from 375 hospitals)

Hall, EJ. Radiobiology for the radiologist. Philadelphia, PA: J.B. Lippincott Company; 1984.

National Council on Radiation Protection and Measurements. Limitation of exposure to ionizing radiation. Bethesda, MD: NCRP; NCRP Report 116; 1993.