Answer to Question #15333 Submitted to "Ask the Experts"

Recently I had two CTAs (computed tomography angiogram) and a cerebral angiogram, which is an interventional radiology procedure that utilizes a catheter. I know the risk from a CTA is very small and was told the risk from the cerebral angiogram would be less than the CTAs. After the cerebral angiogram, I asked how much radiation was used and was advised that the amount is 1200 mGy. I am panicking. This is a very large dose. I am hoping I misunderstood or that I am missing something, and I didn't receive over 1 Sv of radiation into my brain, thyroid, eyes, and sinuses. Is interventional radiology/fluoroscopy different from CT and typical x rays in terms of potential harm?

You did not receive a large radiation dose, and your additional risk of cancer is negligible. Let me try to unwrap the radiation dose information that you were given so that perhaps it is clearer.

As you note, the risk from a computed tomography angiogram (CTA) of your head is very small. In order to be able to discuss risk from different procedures, we speak of the effective dose. The effective dose is the radiation dose to your entire body that would have the same risk as the dose from the procedure. When your providers said that the radiation dose from the cerebral angiogram was less than from the two head CTAs, they were referring to the effective dose of the procedures. While I clearly do not have all the information your providers had in making that assessment, their result is in the expected range of effective doses for cerebral angiograms.

But what is the dose of 1200 mGy that was reported to you? Fluoroscopy, like that used in the cerebral angiogram, delivers a much higher radiation dose to the skin at the location viewed than it does to deeper tissues. The 1200 mGy is a skin dose one might see at the site from fluoroscopy. A concern when doing these examinations is potential damage to the skin. Erythema (skin reddening similar to sunburn) can occur at skin doses as low as 2000 mGy. I believe your providers were intending to communicate that the local skin dose from your procedure was well below what would lead to erythema. Since the dose to deeper tissue is much smaller and the area receiving this skin dose is small, this local skin dose still equates to a very small effective dose.

Briefly, let me note that the dose from scattered radiation will be much less than from direct radiation. Also, radiation dose drops off rapidly with distance, so at a short distance from your head the dose from scatter radiation will have decreased a great deal more. More importantly, when looking at effective dose from medical procedures, scatter radiation has been included in the evaluation.

Please do not worry about the risk from these three procedures. I am sure they provided information to your care team that will help them to help you. The effective dose from these procedures was very small and has not caused potential harm.

Keith Brown, PhD, CHP