Dosimetry for synchrotron stereotactic radiotherapy: Fricke gel and Monte Carlo calculations

In Synchrotron stereotactic radiotherapy (SSR) the tumor is loaded with atoms of high atomic number (Z) element, and exposed to monochromatic X-rays from a synchrotron source (50-100 keV), in stereotactic conditions. This method is under investigation at the European Synchrotron Radiation Facility (ESRF) for the treatment of brain tumors. Conventional treatment planning systems are not suitable for SSR since the beam energy, the irradiation geometry and the presence of high Z elements differ from commercial systems. Therefore, SSR requires the development of new procedures for the evaluation of dose maps. Monte Carlo (MC) method offers the potential of calculating the dose in complicated geometries, made of heterogeneous materials. MC calculations were performed using the MCNP4C general purpose code. Gel dosimetry allows accurate experimental verification of three-dimensional absorbed dose distributions from any irradiation geometries. In this study, the Fricke chemical dosimeter was employed for it is easy to prepare without special facilities. Various phantoms filled with Fricke gel were irradiated in SSR configuration. The dose profiles obtained were compared with MC simulations.