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

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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.