Clinical Aspects of Supervoltage Roentgen Therapy in Cancer

Abstract

THE supervoltage apparatus used by our group since 1933 has been described on several previous occasions. Essentially, the tube is a copy of one built by Professor C. C. Lauritsen at the California Institute of Technology. The valve tube transformer circuit is of the Villard type. The voltage used is 525 to 550 kv. The focal skin distance is 52 cm. and the filtration equivalent to 0.8 mm. lead (half value layer 0.56 mm. lead and 2.8 cm. aluminum). The current through the tube is approximately 3.2 ma., the output being 15 r per minute. The effective wave length is 0.044 Ångstrom (Fig. 1). In the treatment of deep-seated malignancies, it has been shown in the past that, as voltages have been increased, the five-year cures have been increased. Changing from 130 to 140 kv. to 200 kv. was a definite advance. With the advent of supervoltages, in the realm of 500 kv. or more, it was hoped that results would be markedly improved, as absorption of greater intensities in the depths might be expected. It was thought that larger total dosages might be administered, as there would be less skin injury with the supervoltages, due to a decrease in back-scatter and an increase in forward-scatter. A comparison between patients treated in the past with 200 kv. and those treated with supervoltage in more recent years, is almost impossible because other factors beside voltage have been variable. The mode of application of roentgen therapy, fractionation of dosage, time factor of individual applications, and total elapsed time of the entire series have all been altered. These are all very important factors and each may be just as important as the factor of voltage. A description of some of the various lesions treated by means of supervoltage will be given. Carcinoma of the Inner Surface of the Cheek.—This is usually of low grade malignancy and quite resistant to irradiation. We selected a few specimen cases of these conditions for treatment by fractionated supervoltage alone. As these lesions were rather near the surface, adequate dosage could have been secured by lower voltages. The tumor in these cases received about 80 per cent of the surface dosage (as measured by the Lauritsen chamber). Table I shows the method of treatment in these cases, with dosage and results. We realize that fractionated dosage with the ordinary 200 kv. might have accomplished the same result with proper filtration and prolongation of dosage (although, personally, we have never been able to secure similar regressions with 200 kv.). The total dosage of supervoltage in these patients was not large. The majority received a total of about 3,000 r (air), given at the rate of 150 r daily. In some cases the treatment was completed without definite erythema. In none of these cases have there been any late skin changes, telangiectasia or fibrosis, and, in all, the texture of the skin at the present time appears perfectly normal. Carcinoma of the Esophagus.