Time- and dose-related changes in the thickness of skin in the pig after irradiation with single doses of thulium-170 beta particles

Time-related changes in skin thickness have been evaluated in the pig using a noninvasive ultrasound technique after exposure to a range of single dos es of 0.97 MeV beta particles from Tm-170 plaques. The reduction in relativ e skin thickness developed in two phases; the separation into two phases wa s statistically justified only after 120 Gy (P = 0.04). The first phase was between 12 weeks and 24 weeks after irradiation. No further changes were s een until 48-60 weeks after irradiation, when a second phase of skin thinni ng was observed. No further changes in relative skin thickness were seen in the followup period of 104 weeks. The timing of these phases of relative s kin thinning was totally independent of the radiation dose; however, the se verity of each phase of radiation-induced skin thinning was related to the dose, The pattern of changes was similar to that reported previously after irradiation with 2.27 MeV beta particles from Sr-90/Y-90, but the degree of dermal thinning was less for a similar skin surface dose, From a compariso n of the depth-dose distribution of the beta particles from the two radionu clides, it was concluded that the target cell population responsible for bo th the first and second phase of skin thinning in pig skin after irradiatio n may be located at approximately 800 mu m depth. This corresponds to an ar ea in the reticular dermis in pig skin and may be the appropriate site at w hich to measure the average dose to the dermal tissue. (C) 2000 by Radiatio n Research Society.