The Experimental Determination of the Dose Distribution around Yttrium-90 Sources Suitable for Pituitary Implantation

Abstract

The sources under consideration are of sintered yttria rod (⁹⁰Y), 1 mm in diameter and from 2 to 8 mm in length. The method of evaluating depth dose data is described; Mix D is used as a tissue-equivalent absorber and film as a detector, calibrated by means of a standard ⁹⁰Sr plaque. The validity of this method is discussed. The data presented consist of calibration factors (e.g. a 6 mm rod of 1 mc activity delivers at a point on the minor axis 1 mm away from the surface of the rod a total dose of 460 000 rads), depth dose curves and isodose contours. The depth dose curves are exponential in form, the approximate values of the half-value layer thickness in unit density material being 1 mm. The isodose contours are shown to be approximately elliptical in form. From the data presented it is possible to construct isodose surface around these rods of ⁹⁰Y within known limits of error.