Answer to Question #4879 Submitted to "Ask the Experts"

Q

I recently had a fluoroscopy exam on my shoulder which required contrast, except the doctor had excessive difficulty injecting the contrast, making me stay under the fluoroscope much too long. I am afraid I will get cancer now. I asked the hospital to calculate my dose and was told it was about 4.3 minutes fluoroscopy time at the 17 cm Image Intensifier mode at 5.0 R/min. I was told this was a very conservative approach assuming a thickness of six inches for the irradiated part. The entrance skin exposure (ESE) was 21.5 R. They followed this up with one 10 x 12 film centered on the shoulder at 60 kVp and 5.0 mAs. The ESE from radiography was 35.0 mR. The total ESE from these exams was 21.535 R. Isn't this too much? I thought anything over 10 R was cancer causing and/or life threatening—or is the actual dose less because it was only ESE? How much radiation did I get from this? Should I be worried? I have had so many other x rays and fluoroscopy exams in my life, and I am only 40, I'm afraid I've had too much, especially when combined together with so many exams which I haven't even begun to mention here.

A

Thank you for your question and for obtaining the dose information, which is very helpful for us. I'm going to focus on the 21.5 R ESE because the additional 0.035 R really doesn't add anything relative to biological risk.

You are asking about the 21.5 R and possible biological effects. A paper on the Food and Drug Administration (FDA) Web site indicates that the threshold dose for transient erythema (a redness that will come on like a sunburn and then fade) is around 200 rad (for our purposes, I am going to use "R" and "rad" and "rem" interchangeably; they are all units of radiation exposure/dose and for x rays are pretty similar). Doses higher than 200 rad to the skin can, depending on the size of the dose, cause hair to fall out, tissue scarring, and, eventually, irreparable damage caused by skin ulcers. The dose you cite is nowhere near the doses expected to cause a biological effect on the skin.

I'm not sure where the 10 R that you mention comes from. My suspicion is that you might be thinking of a relative whole-body radiation dose. Perhaps you read something that said doses below 10 R are not shown to cause cancer or are less likely to cause cancer than doses above 10 R. In general, that would be true for whole-body doses—if you were in a situation where your whole body would be exposed to 10 R, your chances of getting cancer would be increased.

Since it was only your shoulder—actually the skin of your shoulder—exposed to the 21.5 R, any additional risk of cancer, if it exists, is uncertain.

There is a calculation where we can take the exposure of a small part of the body and roughly determine what it is equivalent to from a whole-body exposure point of view. This equivalent whole-body dose is called the "whole-body effective dose" or just "effective dose" (see http://http://hps.org/publicinformation/ate/cat51.html, under "Calculating Doses"). We do this only to try to compare doses and risks from various studies that use radiation. For instance, a two-view chest x ray exposes the skin of the chest to about 0.04 to 0.05 R. That equates roughly to a whole-body effective dose of 0.006 rem. So, what we're saying is that the risk of a standard two-view chest x ray is close to the risk of your whole body getting 0.006 rem (which is on the order of six days of background radiation).

If you're still with me (and I hope so), I did this calculation for your 21.5 R ESE shoulder. I calculated an effective whole-body dose of about 0.49 rem. To put that in perspective, it is one-tenth the annual radiation dose limit for a radiation worker. It is very close to the allowable level of radiation a family member can receive when a loved one is released from the hospital with radioactive material inside him/her. It is also very roughly equivalent to about two years' exposure to typical levels of background radiation. I won't relate it to a cancer risk because your whole body didn't get that radiation so it doesn't apply.

I hope this information is helpful. The FDA Web site might also be helpful. It has some very good information about radiation (especially fluoroscopy) and potential biological effects.

Kelly Classic
Certified Medical Health Physicist