Dan L. Fanselow

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).

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.

Reusable ultraviolet monitors: Design, characteristics, and efficacy‡

Reusable ultraviolet dosimetry badges have been developed that provide a visual indication of daily cumulative ultraviolet (UV) exposure. These two-sided, tapelike devices measure UV radiation emitted by sunlight or an artificial UV light source exposure by means of a photochromic aziridine color change reaction that is UV-integrating but optically reversible. UV radiation falling on the exposure side of the badge generates a color change that can be seen from the opposite or readout side. End points are indicated by a visual match of the photochromic with a surrounding reference. This paper describes the construction, component characteristics, and clinical testing of two versions of a new photochromic dosimeter that selectively responds to either UVB (280-320 nm) radiation or UVA (320-400 nm) radiation of the solar spectrum. One version of this monitor, sensitive only to the mid-range UVB, has a peak sensitivity to 300 nm and has four end point markers revealing color changes corresponding to 0.4, 0.8, 2.2, and 6.5 times the minimal erythema dose of an average Caucasian. A second version, sensitive only to UVA, has a peak sensitivity at 355 nm and can monitor exposures ranging from 0.8 to 10 joules/cm2. Outdoor efficacy testing has shown that the UVB monitor is an effective predictor of UV dose-related 24-hour erythema response induced by sunlight. Following a measurement, these monitors can be rezeroed by exposing the readout side to sunlight for a few minutes. They can be reused for eight to ten times. The limitation of the sunlight-calibrated UVB monitor tag is its failure to predict erythema response produced by artificial UVB sources such as FS40 sunlamps.