HE LOCAL radiocurability of tumors varies
T with the clinical stage, histological type,5 and systemic conditions19 4 for a given type of treatment. Differentiating tumors at various accessible sites3 and at the same sit@ are more amenable to radiotherapy than are anaplastic cancers of comparable clinical extent, and, since these 2 tumor types differ in the number of viable cells per unit volume, it might be argued that the number of cells in a given tumor in relation to a constant dose of radiation determines the outcome of treatment. Recently attention has been focused again on the role of oxygen in the radiocurability of tumors.9 It has been suggested that there is a falling gradient of oxygen tension from the periphery to the center of tumor foci,lO and, since the effects of radiation increase with oxygen tension,8 i t might be expected that tumors with large foci would prove more radioresistant than would those with small foci in which the central cells are still within reach of the oxygen supplied by the vessels in the surrounding stroma. Thus it might be the supply of oxygen to a given focus and not the number of cells within it that accounts for its sensitivity or refractoriness to radiation.
In the present paper an analysis is presented of the role of the predominant size of tumor foci on local radiocurability and at the same time the effect of the histological type and clinical stage are re-evaluated with reference to the size of tumor foci. An attempt is made to answer the following questions: Does the size of tumor foci affect the local radiocurability of a tumor? Is the size of tumor