Studies on Cell-survival of Irradiated Ehrlich Ascites Tumour

Summary

1. The survival curves obtained with a hypo-diploid Ehrlich ascites carcinoma after irradiation with x-rays in either oxygen or nitrogen are compared with those previously reported for a near-tetraploid tumour.

2. The radiosensitivity of the two cell-lines, as defined by the slope of the exponential part of the survival curves, is the same when the irradiations are in oxygen.

3. Anoxia lowers the radiosensitivity of the diploid tumour by a factor of 2·7 and that of the tetraploid tumour by 3·1.

4. The extrapolation of the exponential part of the survival curves to zero dose results in an intercept of 2·4 for the diploid tumour compared with approximately 10 for the tetraploid tumour.

5. The significance of a high extrapolation number in the fractionated radiation treatment of spontaneous tumours is discussed.