Animal experiments in radiotherapy III: large versus small animals.

An evaluation is made of the conflicting claims of large and small animals as models in experimental radiotherapy. The pro's and con's of each are examined in relationship to both tumor and normal tissue studies. It is concluded that there are few, if any, tumor-related studies in which large animals are preferable, and that a somewhat similar situation exists with investigations of early reactions on normal tissues (at least to the extent that these are governed by the cell survival curve). The conclusion emerges, however, that a large animal may be required in certain investigations of late effects. Examples of the very different late effect tolerance levels between mouse and man are given.