A Factor of Importance in the Radio Sensitivity of Tumours

Cells forming the margins of carcinomatous cell masses are more sensitive to gamma radiation than the central cells. A reasonable explanation for this is that the marginal cells have a more abundant oxygen supply, being near the blood-vessels, and are for this reason more radio-sensitive, since cells under anaerobiosis are radio-resistant. If this be the case, then carcinomas having small cell masses should be more radio-sensitive than those with large cell masses. This deducation is considered, and evidence in its favour discovered. The question of the importance of the macrophage reaction to be seen in tumours regressing after radiation is discussed, and it is concluded that they play no more important part than the phagocytosis of cells killed by the radiation. Conclusion is drawn that repeated doses of radiation should be spaced so as always to catch the tumour in a radio-sensitive state, and that radiation should be withheld during times of radio resistance, following previous radiation. It is suggested that the growth of tumours will supply a measure of their radio sensitivity during life; growth corresponding with sensitivity, and regression with resistance.