Toward a novel simplifed microdosimeter for the clinical environment

Radiation therapy with protons and ions is gaining popularity all over the world, because of the physical and biological advances with respect to photon, electron and neutron radiotherapy. At present, sixty-four therapeutic centers worldwide use particle beams to treat their patients. Most of them use fast protons beams and ten centers (3 in Europe, 5 in Japan and 2 in China) use carbon ions. A definite model of radiation action on living cells is still unestablished, however it is known that the “quantity” of radiation, characterized by the absorbed dose (the mean energy imparted to matter per unit mass) is not sufficient to characterize the biological effect, in that equal doses of different radiations lead to different results. Sparsely ionizing radiations, like gamma rays, are less effective than densely ionizing radiations, like slow protons and carbon ions; the capability of ionizing radiation to damage a living cell is indeed closely related to the local energy deposition within relevant subcellular structures, like the chromosomes. An accurate treatment planning should therefore take into account the particle interactions at the micrometer level. To this respect, microdosimetry offers a valuable technique, by measuring the stochastics of energy deposition in small volumes of approximately 1 m size. Tissue-equivalent gas proportional counters (TEPC) are the reference devices. A miniaturized TEPC has been build at the Legnaro National Laboratories of LNL, to cope with high intensity therapeutic beams used at the Centro Nazionale di Adroterapia Oncologica (CNAO) of Pavia. The objective of this thesis is to study in detail the working characteristics of this mini-TEPC, with the aim to design a novel simplified microdosimeter optimized for the clinical environment.