The influence of dose rate on ultraviolet tumorigenesis

To gain an insight into the relationship between the time in which a daily UV dose is delivered and its carcinogenic effectiveness, the following experiment was performed. Three groups of 24 albino hairless mice (Skh-hr1) were exposed to the same daily dose of UVB radiation (600 J m-2; Philips TL12). The exposure times for the three groups were 1.25, 4 and 12 h per day. A fourth unirradiated group served as a control. All animals exposed to UVB developed multiple skin tumours, whereas the control animals did not develop any observable tumours. Tumour development in the groups exposed for 4 and 12 h was virtually identical. Tumour development was significantly faster in the groups exposed for 4 and 12 h per day than in the group exposed for 1.25 h: the median tumour induction time was reduced by 12%. In terms of the effective dose, this is equivalent to a 25% increase in effectiveness for the 4 and 12 h groups relative to the 1.25 h group. In conclusion, the present experiment shows that prolongation of the exposure duration increases the carcinogenic efficacy of UVB radiation.     

OZONE DEPLETION AND INCREASE IN ANNUAL CARCINOGENIC ULTRAVIOLET DOSE

An increase in skin cancer incidence due to an increase of solar ultraviolet (UV) radiation is one of the best quantitated effects of stratospheric ozone depletion. Until now, estimates of effective UV dosages could not be based on spectral data on carcinogenicity. Instead the spectral dependence of sunburn or mutations was used. These data contained little information on longwave ultraviolet radiation (UVA: 315-380 nm). Recently, in hairless mice, experimental data have become available on the carcinogenic effectiveness of the ultraviolet, including UVA. From these new data we can estimate the effect of ozone depletion on the ambient annual carcinogenic UV dose. We find that a 1% decrease in ozone yields a 1.56% increase in annual carcinogenic UV; this value is not strongly dependent on geographical latitude. From this result, combined with the dose-response relationship for UV carcinogenesis, we conclude that for a 1% decrease in total column atmospheric ozone an increase of 2.7% in non-melanoma skin cancer is to be expected.     

EVALUATION OF SKIN CANCER RISK RESULTING FROM LONG TERM OCCUPATIONAL EXPOSURE TO RADIATION FROM ULTRAVIOLET LASERS IN THE RANGE FROM 190 TO 400 nm

The relative risk of occupational exposure to radiation from UV lasers was estimated using a mathematical model based on both epidemiological data and animal experiments. Calculations were performed for the 193 nm ArF excimer laser cornea shaping, the 308 nm XeCl excimer laser for coronary angioplasty, and other UV lasers in a laboratory environment. The model included the effects of direct exposure and exposure to scattered radiation. The results show that for the two medical applications the increase in the relative risk is comparable to that of one additional day of sunbathing per year. For subjects exposed to UV lasers in a laboratory setting, the relative risk may increase to a value comparable to that of people with an outdoor profession.