Dosimetry in phototherapy cabinets

Many skin diseases can be treated with phototherapy. The dose of ultraviolet radiation received at the skin surface should be recorded to guide subsequent treatment doses as well as to monitor cumulative dose. In order to see if a single reading from an electric dosimeter accurately reflected the dose of ultraviolet radiation received at the skin surface, 212 photoresponsive dosimeter badges were affixed at various sites to the skin of one side of a female volunteer. The volunteer was then exposed to ultraviolet A (UVA) radiation in a UVA light treatment cabinet. The monitors were then removed and the received dose recorded. Portions of the body facing the lights directly received the most irradiation. Areas inclined to the plane of the lamps, shaded areas, and anatomic areas near the top and bottom of the cabinet received the least. Dosimetry as recorded by an electronic monitor in the center of the cabinet decreased when a subject stood next to it. Evidently a single measurement of dose by an electronic monitor in an empty treatment cabinet does not necessarily reflect the amount of ultraviolet radiation received at any given anatomic site by a patient undergoing phototherapy.