Regionally Fractionated X-Irradiation Equivalent in Dose to Total-Body Exposure

Abstract

The effect of shielding various portions of the body on radiation mortality has been studied by numerous investigators (1-10). Attempts to explain the markedly decreased mortality that is generally observed when relatively large body regions are shielded have been based primarily on considerations of the radiosensitivity of the tissues exposed, the importance of the functional integrity of these tissues in the total economy of the animal, and the volume-dose received. It is now apparent that still another factor must be considered in evaluating the results of partial body irradiation whether large or small regions are shielded, namely, the influence of possible substances emanating from normal tissues which are capable of enhancing regeneration of radiation-damaged tissues. A considerable body of presumptive evidence for the existence of such a substance (or substances) has accumulated. Jacobson (11) obtained increased survival and/or accelerated hematopoietic recovery by shielding the spleen during irradiation and by post-irradiation spleen implantation or injection of an embryo suspension. Similar beneficial results were demonstrated by Lorenz and associates (12, 13) after a post-irradiation injection of bone marrow and by Cole et al. (14) after injection of a homogenate of spleen. The results of these investigations strongly suggest that the factor (or factors) involved is humoral in nature, although they do not establish whether or not its production and availability in effective quantities depend upon the presence of living cells in the material administered (11, 13). However, Cole et al. (15) have recently obtained a cell nuclei fraction from mouse spleen tissue that effectively decreases radiation mortality, furnishing strong evidence that the presence of living donor cells in the irradiated recipient is not necessarily required. The available data suggest that hematopoietic or reticuloendothelial tissues are primarily concerned in the production and utilization of the active material; however, it is possible that other tissues may also elaborate and/or be affected by the