| Description |
In adult beagles, the initial retention of 226Ra for 1 eye was 0.071 % of the injected dose at all dose-levels tested. The biological half-times for eye retention varied inversely with the amount of the injected dose and appeared to be a function of the degree of radiation-induced injury. Within the eye, nearly all of the radium was retained in the pigment granules of the respective melanotic tissues, including the tapetum lucidum. This localized retention pattern produced radiation-induced focal lesions that were restricted principally to the pigmented components. The highest doe levels (1.07 to 10.4 µCi226Ra/kg) produced a significant reduction in the number of branched melanocytes and an increase in the number of round clump-like pigment cells of the uvea. The clinical appearance of this change was characterized by fading of the iris, depigmentation of the choroids, and partial or complete loss of the tapetum. The lower dose levels produced very little changed in the branched pigment cells but induced a significant increase in the round pigmented cells. This resulted in hyperpigmented foci or nevi that were especially obvious on the iris. The source of the round clump-like cells, which increased in all dose levels, appeared to be the pigment epithelial layer. This layer within the ciliary body was the most reactive site, with much lesser changes occurring in the choroids and little or no change in the iris. The round pigment cells observed in the iris appeared to arise from the ciliary body. Qualitatively similar lesions were induced by 224Ra, 226 Ra, 228Th, and to a lesser extent , by 239 Pu and 90Sr. Of the various endpoints in the radiation induced eye syndrome, neoplasia was the most ominous. All of the 24 tumors were melanomas which appeared after long latent periods. The highest incidence was observed in the dogs injected with relatively low dose levels of 226 Ra (0.0621 to 1.07 µCi226Ra/jg), 228 Ra (0.0177 to 0.148 µCi228Ra/kg), and 228Th (0.0152 to 0.0302 µCi228Th/kg). They have not occurred in the 239Pu, or 90Sr treated animals. All but one of the eye tumors arose in the ciliary body and the pigment epithelial layer tentatively appeared to be the primary point of origin. The data presented in this thesis is from an on-going study and is current through July 1, 1970. |
