Comparison of Various Sources of Interstitial Radiation

Abstract

THE importance of interstitial radiation in cancer therapy is constantly being emphasized. It is now recognized that it is impossible to deal adequately with some types of lesion by external irradiation alone, but that many of these can be controlled by the judicious use of radium or radon needles, or radon seeds. Up to the present time the dosage for these buried sources has been largely developed empirically by each radiologist for himself, except in the case of the gold radon seeds. For these, on a basis of experimental data, a practical system of dosage has been developed which is very satisfactory for lesions up to several centimeters in diameter (1, 2). For various types of implants there has been so far very little basis for comparison. Dosages employed in one clinic could not be related to those in others using somewhat different types of sources. It has thus been difficult to duplicate treatments in different clinics, unless the implants employed happened to be the same size and strength. Some time ago a preliminary paper was published correlating the effects of weak (1–4 mc.) radon seeds, permanent or removable, and certain 1 mg. radium needles, in bleaching butter (3). This work has now been extended to certain 5 and 10 mg. needles and seeds up to 11 mc., of various lengths. In addition to the use of the butter medium, the production of tissue necrosis in the dorsal muscles of rabbits has been employed. The purpose of the present paper is to present the results of these experiments and some conclusions drawn from them. There is considerable variation among the types of implant in use. Most of the filtered permanent radon implants (gold seeds) have a filter of from 0.25 to 0.35 mm. gold, and a length of 4 or 5 millimeters. The removable radon implants have a filter of from 0.25 to 0.3 mm. platinum, and are 5 or 6 mm. long. The strengths of either of these may range from a fraction of a millicurie to four or five millicuries—seldom more. Such small differences in filtration and length may easily be corrected for, or neglected for a first approximation. On the other hand, the needles may have filtrations varying from 0.25 mm. steel or monel metal to 0.5 mm. or more of platinum, and may range in length from a few millimeters to several centimeters. Obviously this part of the problem is much more difficult. It is impracticable to cover the whole range experimentally, but a good deal of information can be obtained from a detailed study of relations between a few types of implants. The sources of radiation used in the present study were gold seeds and platinum radium needles. Detailed specifications are given in Table I. The two reactions used, as already stated, were the bleaching of butter and the formation of tissue necrosis. The bleaching of butter has been used in a great deal of work regarding dosage from both gold and glass seeds, and its use has been discussed in previous papers (4, 5).