Relation between the Radiation Dose Tolerated by the Skin and the Distance of the Radiant Source from the Skin

Abstract

The surface dosage of gamma-rays required to produce a certain degree of skin reaction by radium therapy depends on the distance between the radiophore and the surface of the skin. At small distances a 5-times greater surface dose may be applied than at greater distances. On the basis of empirically determined application times and of graphs showing the dependence of the intensity of radiation on distance it could be demonstrated that the depth dose 4 mm. below the surface is responsible for the reaction of the skin. In all cases, with distances of 0.25-8 cm., the same degree of reaction is obtained if the dose 4 mm. below the surface is 3500 [plus or minus] 600 r. Dosage figures obtained with ionization chambers of an external diameter of 7-8 mm. are convenient for all types of surface applicators.