Reusable ultraviolet monitors: design, characteristics, and efficacy

The Early Days of Personal Solar Ultraviolet Dosimetry

In the early 1970s, environmental conservationists were becoming concerned that a reduction in the thickness of the atmospheric ozone layer would lead to increased levels of ultraviolet (UV) radiation at ground level, resulting in higher population exposure to UV and subsequent harm, especially a rise in skin cancer. At the time, no measurements had been reported on the normal levels of solar UV radiation which populations received in their usual environment, so this lack of data, coupled with increasing concerns about the impact to human health, led to the development of simple devices that monitored personal UV exposure. The first and most widely used UV dosimeter was the polymer film, polysulphone, and this review describes its properties and some of the pioneering studies using the dosimeter that led to a quantitative understanding of human exposure to sunlight in a variety of behavioral, occupational, and geographical settings.

A solar erythemal (sunburn) radiation dosimeter

Measurement of solar erythemal radiation is a technically demanding task because it is accompanied by a vastly greater flux of other solar radiation. An inexpensive solar erythemal radiation dosimeter has been designed which is based on the photocleavage of an alkyl disulphide. The reaction is carried out in a hydrocarbon solvent which can readily donate hydrogen atoms and as a result no polysulphides with absorptions in the erythemal action spectrum were formed. This avoided non-linearities in the dosimeter arising from inner filtering effects. The amount of alkylthiol produced as a result of exposure of the corresponding dialkyl disulphide solution to solar erythemal radiation was linearly related to the dose of radiation received.

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.

Photobiology of melanin pigmentation: dose/response of skin to sunlight and its contents

A randomized double-blind clinical trial involving twenty-two volunteers was conducted in two locations (Orlando, FL, and St. Paul, MN) to test the efficacy of the newly designed ultraviolet monitor badges (Sun Timers), described in another paper by us in this issue of the Journal, 1 and to establish the relationship between spectral band exposure dose and the biologic responses of erythema and pigmentation. Individuals with skin types II, III, and IV, exhibiting differences in reactivity to solar radiation, were exposed to varying doses of full-spectrum sunlight through templates mounted on the lower portion of the back. Simultaneously, on the upper portion of the back, the same volunteers were exposed through two different types of polyester filters that transmitted ultraviolet A (UVA) and visible radiation. Using templates with windows, exposures to full-spectrum sunlight, UVA, and visible radiation were carried out to 1, 2, 3, 6, and 9 sunburn units (approximately 30-270 millijoules/cm2 between 10:30 A.M. and 3:30 P.M. daylight time in mid summer), measured with the aid of a Robertson-Berger meter and an IL700 International Light radiometer. Erythema and pigmentation resulting from these exposures were graded (double-blind) immediately after exposure, at 24 hours, and after 5 days. Numerical skin response ratings at each exposure dose for different spectral bands were then averaged and plotted. It was found that the UVB monitor response was predictive of a 24-hour erythema response and 5-day pigmentation response within 30% of the biologic average for skin types II, III, and IV. UVA radiation stimulated melanogenesis. The minimal melanogenic dose (MMD) for skin type II was the same as the minimal erythemogenic dose (MED). The MMD for individuals of skin types III and IV was distinctly less than their MED. Thus, melanogenesis can be stimulated with a suberythemal dose of UVB or UVA radiation. The sun protection factor values of melanin for melanized skin have been estimated to vary from 1.0 (skin type II) to 4.3 (skin types V and VI).