The Skin Erythema for Combinations of Gamma and Roentgen Rays

THE reaction of the skin is a very important factor in external radiation therapy, since, in general, it limits the dose that can be administered. Consequently, any scheme which made possible the use of a larger amount of effective radiation without injury to the skin, would be of value. Recently some clinical evidence has been brought forward to show that when treatment is given by means of a combination of gamma and roentgen rays, the skin reaction is less marked than when only one type of radiation is used. It seems worth while to investigate this matter, to see whether this is really the case, or whether the idea is based on erroneous determinations of the magnitudes of the radium and roentgen-ray doses administered. If it is found to be true, there remains the further problem of whether this combined treatment is more effective from the point of view of tumor regression. That depends on the possible selective response of the tissues to the radiations employed, and is entirely outside the scope of the present study. The method of measuring the radiation administered is of primary importance. No physical means would be satisfactory, since it has not yet been shown that skin reaction is proportional to ionization or to any other physical phenomenon, over the range of radiations to be considered. The best, and simplest, way is to measure the radiation by the phenomenon being studied, the skin erythema. This makes unnecessary the use of any measuring instrument except to check the constancy of the roentgen-ray output. In our case it was found that under the same conditions (voltage, milliamperage, etc.), the roentgen-ray machine emits the same quantity of radiation from day to day, within very narrow limits. The radium, of course, will not change during the time of the research. A method for investigating the effect of combining two types of radiation by this means has been used by one of us (E. H. Q.) in a study of the erythema dose for a combination of beta and gamma rays (1). It consists in, first, determining the separate erythema doses for the given types of radiation, and then in making tests of the skin reaction with combinations of the two. If 50 per cent of the erythema dose for one type, followed immediately by 50 per cent of the dose for the other, produces the same effect as 100 per cent of either one alone, then the combined dose, according to our standard, is the same as either single one. But if it takes, say, 60 per cent of each to produce the same reaction as 100 per cent of either, then the combined dose is less; there is an increase in the total amount that must be administered to produce the effect. In other words, the skin will stand more radiation if it is combined in this manner. As we have already stated, this gives no information about the therapeutic effects of the combination.