Experimental Microdosimetry for clinical Hadron Therapy

Hadron therapy is an effective, fast growing radiotherapy technique using protons or light-ions to confine the radiation damage within the tumor with challenging precision. Charged particles produce unique pattern of ionizations which can enhance their biological effectiveness. Microdosimetry is a branch of radiation science which aims to investigate the stochastic nature of radiation-matter interaction by measuring the single-event energy deposition in cell-like volumes and its distribution. However, there are neither well-established devices nor accepted protocols and codes of practice yet. Combined radiobiological-microdosimetry measurements to identify key parameters and how to link physics measurements to biological outcome are needed to standardize microdosimetry. Solid-state microdosimeters are a promising microdosimetry technology. In particular, diamond looks to be an optimal material to use for its fairly tissue equivalence, high radiation hardness, fast time response and high signal to noise ratio. Our research project aims to develop the best experimental system for diamond-based microdosimeters to be used in clinical facilities. Efforts will be focused on studying a reliable calibration method, exploring the use of single-stage as well as telescope devices, studying the impact of the detector thickness and sensitive area, improve reproducibility and implementing a front-end electronic able to accommodate the high counting rate of the detectors and to minimize the magnetic field disturbances caused by the accelerator facility and the electronic noise. An experimental system has been implemented and tested for α-particle measurements and first microdosimetric spectra have been acquired. The acquisition system was tested through a pulse generator to study its frequency response. Further experiments with the α-system will investigate the role of bias voltage and signal-to-noise level. Measurements with ion beams in clinical settings have been planned