Permanent Planar Iodine-125 Implants: The Dosimetric Effect of Geometric Parameters for Idealized Source Configurations

Abstract

To provide dosimetric information about permanent planar (125)I implants in a manner that is useful to the brachytherapist in the operative setting. Reference planar permanent implants were simulated for a variety of areas with sources placed uniformly on a 1-cm grid. Implants having variable source spacing and curvature were simulated and compared with the reference implants. Dosimetric measures were calculated at 0.5 and 1.0 cm from the implant plane. A method for calculating dosimetric statistics for permanent implants ranging from 5 x 5 cm to 13 x 13 cm is presented. A formula to predict the reference source strength needed to achieve a desired dosimetric quantity is also presented. The effect of adjusting strand spacing to compensate for source activity is presented and is shown to be an effective means to adjust implants to use source strengths other than the reference strength. The effect of implant curvature compared with flat implants on dosimetric statistics is presented as a function of radius of curvature. The results presented in this work may be used to provide information about dose delivered from planar permanent implants.