Use of Autoradiographs to Detect Defects in Radium Needles and Tubes and Inequalities in the Distribution of the Radium

It is now well recognized by most radiation therapists that careful preliminary planning and dosage calculations are essential to good radium therapy. Dosage systems have been published by Quimby (5) and Paterson and Parker (3, 4), which provide rules for the proper distribution of radium sources, and tables and charts for calculating the dosage. These dosage systems are based for the most part on the assumption that the radium sources used are free of defects and that the radium is uniformly distributed along the active length of the source. Badly packed needles, damaged containers permitting leakage of the radium, and faulty distribution of the radium may produce considerable discrepancies in the expected tissue dose as calculated for an assumed uniform packing. It would seem important, therefore, for those employing radium, first to study their radium supply to assure themselves that their sources are properly packed and of the strength and filtration designated by the manufacturer. It is the purpose of this paper to describe a simple method of making autoradiographs of radium needles and tubes which can be carried out by anyone acquainted with the fundamentals of radiography and to present illustrations of defects and inequalities of radium distribution, which seem to emphasize the importance of such a study. Certificates regarding the purity and quantity of the radium are usually supplied by the manufacturer or can be obtained from the U. S. Bureau of Standards. Such certificates are often taken as assurance that all sources are of the stated strength and filtration. However, in order to de crease the cost of measuring the radium content of sources and reduce exposure hazards in handling, it has been the practice of the U. S. Bureau of Standards to measure several radium sources of similar active length and content as a group rather than individually. For instance, ten radium needles of a stated strength of 2 mg. each and 3 cm. active length may be measured together, and a certificate supplied stating that the total radium content of the ten needles is 20 mg. Such a certificate does not necessarily indicate that each of the needles is 2 mg. strength, or that the radium is uniformly packed along its active length. This additional information can be obtained by making autoradiographs of each radium needle and tube. Technics have been described by Griffith (2) and by Russ and Clephan (6) for making autoradiographs, and Clephan (1) has published a suitable formula which can be used as a guide for determining the exposure time required for needles and tubes of varying strengths, diameter, active length, and filtration, with a constant multiplication factor based on the speed of the film emulsion used. This formula is as follows: The factor 10 represents the constant suitable with the use of Ilfiex films, whose emulsion speed appears to be similar to that of Eastman non-screen film.