FRICKE GEL DOSIMETERS FOR THE MEASUREMENT OF THE ANISOTROPY FUNCTION OF A HDR IR-192 BRACHYTHERAPY SOURCE

The anisotropy function F(r,theta) has been recommended to account for the dose distribution anisotropy that results adopting sealed brachytherapy sources. This function is implemented in the American Association of Physicists in Medicine (AAPM) dose calculation formalism and is widely adopted by the currently available treatment planning systems. In this work, a method based on a suitably developed Fricke gel dosimeter with a built-in catheter and on an optical imaging system was developed for the characterization of F(r,theta) for an Ir-192 source. At radial distances of 15, 20, 25 and 30 mm percentage differences between tabulated and measured data resulted to be almost always smaller than 3%. Fricke gel dosimeters result to be accurate tools for the Ir-192 anisotropy function measurement. These instruments could be easily adopted in quality assurance protocolls to verify the anisotropy function of each newly installed Ir-192 source.