AbstractOptimally, the total radiation dose, over-all treatment time, and fractionation should be individualized for every tumour on the basis of histology, the number of malignant cells, the percentage of anoxic cells, and the kinetics of that particular tumour.The histological variety within the epithelial tumours does not affect radiosensitivity. Dose-response curves obtained clinically are shown for subclinical disease in the lymphatic areas. Correlation is attempted between the volume of cancer and the doses necessary to obtain a high percentage of controls. It is shown that, depending upon the anatomical site and the clinical variety of the cancer, the doses and treatment times may be different.Reoxygenation during treatment has been considered necessary to explain the control of human cancers by irradiation. The percentage of controls of very large, poorly vascularized tumour masses irradiated with long treatment times compared with shorter treatment times suggests that reoxygenation may be a factor.Some reflections are made on the repopulation potential of malignant cells by comparing results obtained with the split-course technique versus 850 rads weekly dosage rate.