Answer to Question #1325 Submitted to "Ask the Experts"

Q

I need to make a table that shows a correlation between electron beam energy (kGy) and ultraviolet (UV)—sun exposure for the same amount of time, if we assume we expose the same thickness of mass. I know the mechanism is different, but I would like to have a few values to show the equivalent for absorption in each case. For example: for 1.5 min 0.5kGy . . .? UV rams 0.75kGy . . .? UV rams 1.0kGy . . .? UV rams and so on up to 5 kGy.

A

As you've noted, the radiation absorbed dose and damage mechanisms from an ionizing radiation, such as an electron beam, is not directly comparable to that from nonionizing radiation, such as ultraviolet (UV) radiation. However, in this case the end point erythema may appear to be the same. I suspect you are doing this for discussions with patients undergoing radiation therapy, where skin reddening is a common side effect. If you're looking at the biological effects of UV radiation, you may wish to get a copy of the American Association of Physicists in Medicine Report No. 3 on "Optical Radiations in Medicine." This report notes that "at the wavelength of maximum sensitivity for production of erythema (295 nm), the minimal erythema dose (MED) is 50 joules per square meter. If this energy is absorbed in the outer 60 micrometers of skin, the 'absorbed dose' is equivalent to 100,000 rads!" The AAPM reports are available free to members, but for sale to nonmembers. David J. Allard, CHP