The INFN Micro-Si experiment: A silicon microdosimeter for assessing radiation quality of hadrontherapy beams

The MICRO-SI experiment, funded by INFN from 2008 up to 2010, aimed at developing a silicon microdosimeter capable of responding to neutrons and to hadron-therapy beams down to a few keV μm-1. The main goals which were achieved in the framework of this experiment are described in details. The detector, designed and fabricated by exploiting the monolithic telescope technology, demonstrated to provide charge confinement inside the micrometric sensitive volume, thus minimizing the field-funnelling effect. An innovative segmented telescope device was developed in order to have a silicon detector offering sensitive volume dimensions similar to those which can be simulated by a tissue-equivalent proportional counter (TEPC). The response of the segmented device to hadron beams was characterized with clinical protons and with 62 AMeV carbon ions at the INFN-Laboratori Nazionali del Sud (Catania, Italy). Irradiations with mono-energetic neutrons at the INFN-Laboratori Nazionali di Legnaro (Legnaro, Italy) were also performed. The agreement with the spectra measured with a TEPC is very satisfactory and gives confidence on the application of such a silicon device to assess the quality of hadrontherapy beams.