Commissioning of a Microdosimetric Device for Hadrontherapy

Radiotherapy aims at maximising the dose delivered to the tumour whilst minimising that to the healthy tissues. The absorbed dose, being an average quantity, doesn’t consider the random nature of radiation interactions. However, it is well acknowledged that biological effectiveness is related to the microscopic distribution of absorbed energy rather than to its mean value. If the microscopic distribution is uniform throughout the irradiated volume (for conventional photon-based radiotherapy), the absorbed dose is a suitable parameter. For charged particles (e.g. protons, helium and carbon ions) ionizations are clustered around the particle path and produce a not uniform pattern of energy deposition. In this case average values do not accurately predict the biological effects. In treatment planning systems (TPS) used in proton therapy it is currently assumed that the biological effectiveness is constant, independent of the proton beam energy and penetration depth. However, the scientific community is moving toward advanced protocols in which the change in biological effectiveness is considered. In parallel, procedures for the quality assurance of the radiation quality (physical characteristics of the radiation field correlated to the biological effectiveness) need to be developed. Microdosimetry is a valuable technique, but commercial detectors for hadron-therapy applications are not currently available. The engineering of advanced gas-based microdosimeters for the characterization of proton and carbon ion beams is currently ongoing at Legnaro National Laboratories of INFN. This thesis focuses on the characterization and optimization of new devices in gamma, neutron and therapeutic proton fields. The response function will be studied for several operative conditions of the sensor, front-end electronics and control/data acquisition system.