The use of anisotropic data in 125I prostate implants

The report recently published by AAPM Task Group 43' (TG43) recommends the use of a two dimensional dose distribution function for the dosimetry associated with 125I, 192Ir and 103Pd sources. For commercial planning systems that cannot be readily adapted to use a two dimensional function, a point source approximation is provided. The dose distribution around an array of 125I seeds has been calculated using the two dimensional model and the point source approximation. Isodose distributions through selected planes and dose volume histograms of selected cubic volumes show that differences between the two models for this array are insignificant, particularly in view of the uncertainties associated with using the data which is provided by TG43 for the two dimensional anisotropy function.