Low-Voltage Contact Roentgen Therapy (Chaoul Therapy)

Abstract

In 1931, proceeding on the assumption that it has never been demonstrated that the biological effect of radiation is dependent upon its wave length and that there is, on the contrary, a considerable weight of evidence against such a thesis, Chaoul and Adam began to investigate the possibility of using low-voltage radiation applied under conditions approximating those obtaining in the surface application of radium. Their motivation was, of course, the scarcity and high price of radium in Germany. Briefly stated, their thesis was this: It may be regarded as axiomatic that the effect of radiant energy depends, not on wave length, but on the total energy absorbed per cubic centimeter of tissue, and the time spacing or fractionation of that total energy. Holthusen has compared the results of irradiation of the skin with rays of a quality represented by a half value layer of 0.37 mm. Al, with the results of irradiation of the skin with gamma rays. With equal amounts of energy he found no qualitative or quantitative difference in erythema or epilation, and in another series of experiments he noted no difference in the effects on Ascaris eggs. Englemann has shown that with like amounts of radiation, the morphological changes observed in tumor cells were identical whether low-voltage x-rays or gamma rays were employed. The conditions which obtain in radium therapy (except teleradium therapy), and which it was sought to approximate, are; (1) a short distance between the surface and the source of radiation, (2) a consequent absorption of a large amount of the energy in the first few centimeters of tissue. To fulfill these conditions it was necessary to devise a special apparatus which was shock-proof, which had a very low inherent filter value, and which was so constructed that the anode-surface distance was very short. Furthermore, the radiation produced should be relatively soft, and the fields irradiated should be small. All of these conditions are met in the apparatus which we have employed, namely, the Philips Metalix Contact Therapy Unit (Fig. 1), operating at 50 kv. constant potential, with 2 ma. of current passing through the tube. The tube used is constructed with a metal sheath, is ray-proof, shock-proof, and has a high-tension connection only to the anode, the cathode side being grounded. It is cooled by an air blower. It is cylindrical in shape and measures 23.7 inches in length, with a diameter at its distal end of 1.18 inches. It is, therefore, easily introduced into body cavities and into surgical incisions. The radiation emerges axially, passing through a glass window and a protective cap of a plastic material having a total inherent filter value of 0.2 mm. Al. The anode-surface distance is 18 mm. The tube is usually used with a rubber covering, which adds 2 mm. to the distance, and if filters are employed the total anode-surface distance becomes 22 mm.