Calculation of Dosage from Intracavitary Radiation

Abstract

Prior to the acquisition of radium element in tubes 15.5 and 21.5 mm. long, it was customary at the State Institute to use single or tandem tubes of emanation for intracavitary radiation. The emanation was contained in a bulb with a short stem, which in turn was incased in a metal tube, the walls of which were 0.5 mm. gold and 0.5 mm. brass. The distribution of radiation around tandem tubes of this type is given in an isodose curve by Mattick (1) and by Mattick and Stenstrom (2). When calculating tissue dosage at 3 cm. from tubes of this type, factors were employed in connection with the curves in order to obtain the intensity in per cent of a skin erythema dose. These factors, .06 for one tube of emanation and .04 for two emanation tubes, when multiplied by the total millicurie hours, gave the intensity at the 3 cm. distance. Since the new radium, as the element, was evenly distributed throughout the length of the tube, instead of being concentrated at the ends as in the case of the radon tubes, and since combinations were to be used of one to five 50 mg. tubes and one to three 100 mg. tubes in tandem formation, it was necessary to establish intensity distribution curves for these combinations and also to relate the intensity at 1 cm. distance from each of these combinations to our standard erythema dose. Isodose curves for this type of work have been published by several authors, the extensive work of Friedrich and Glasser being especially comprehensive (3, 4).