Silicon strip detector for a novel 2D dosimetric method for radiotherapy treatment verification

The aim of this work is to characterize a silicon strip detector and its associated data acquisition system, based on discrete electronics, to obtain in a near future absorbed dose maps in axial planes for complex radiotherapy treatments, using a novel technique. The experimental setup is based on two phantom prototypes: the first one is a polyethylene slab phantom used to characterize the detector in terms of linearity, percent depth dose, reproducibility, uniformity and penumbra. The second one is a cylindrical phantom, specifically designed and built to recreate conditions close to those normally found in clinical environments, for treatment planning assessment. This system has been used to study the dosimetric response of the detector, in the axial plane of the phantom, as a function of its angle with respect to the irradiation beam. A software has been developed to operate the rotation of this phantom and to acquire signals from the silicon strip detector. As an innovation, the detector was positioned inside the cylindrical phantom parallel to the beam axis. Irradiation experiments were carried out with a Siemens PRIMUS linac operating in the 6 MV photon mode at the Virgen Macarena Hospital. Monte Carlo simulations were performed using Geant4 toolkit and results were compared to Treatment Planning System (TPS) calculations for the absorbed dose-to-water case. Geant4 simulations were used to estimate the sensitivity of the detector in different experimental configurations, in relation to the absorbed dose in each strip. A final calibration of the detector in this clinical setup was obtained by comparing experimental data with TPS calculations.