QUANTITATION OF THE RADIOTHERAPEUTIC IMPORTANCE OF NATURALLY-HYPOXIC NORMAL-TISSUES FROM COLLATED EXPERIMENTS WITH RODENTS USING SINGLE DOSES

The radiotherapeutic importance, for single doses, of some naturally-hypoxic normal tissues has been deduced from a survey of all known published data using rodents. The importance is derived from the additional doses needed for equivalent damage when normal or malignant tissues are clamped and hence severely -hypoxic. The importance of hypoxia in tumor response shows a marked increase at high single doses. The collated data for all normal tissues demonstrates a similar pattern, thus no marked therapeutic difference is apparent. However, this conclusion is indecisive because the data at low and at high doses pertain to different normal tissue types, and at high doses the data are restricted to 1 tissue, rodent 'skin'. A survey of the dose-dependence of the importance of natural hypoxia in the response of various normal tissues shows that in most cases where hypoxia exists it produces dose-modification. This implies an 'effective' homogeneous low oxygen tension among the critical target cells, in contrast to the heterogeneity in tumors. Thus, slight natural hypoxia in normal tissues may he more important therapeutically than considered previously. © 1979.