MONDO: A neutron tracker for particle therapy secondary emission measurements

In Particle Therapy, cancer treatments are performed using accelerated charged particles whose high irradiation precision and conformity permit to destroy the tumour while sparing the surrounding healthy tissues. Several secondary particles are produced during the treatments mainly photons, protons and neutrons. The reduced attenuation length of neutrons yields a secondary particle sample that is larger in number when compared to photons and charged particles. Since neutrons can release a significant dose far away from the tumour region, a precise measurement of their flux, production energy and angle distributions is eagerly needed in order to improve the Treatment Planning Systems (TPS) software, so to properly take into account not only the normal tissue toxicity in the target region, but also the risk of late complications in the whole body. The MONDO (MOnitor for Neutron Dose in hadrOntherapy) project addresses the technical challenges posed by a neutron detector aiming for high detection efficiency and good backtracking precision. The main goal of the project is to develop a tracking detector targeting fast and ultra-fast secondary neutrons based on the reconstruction of two consequent elastic scattering interactions of a neutron with a target material. By reconstructing the recoiling protons, it is hence possible to measure the energy and incoming direction of the neutron using different therapeutic beams (protons, 12C ions and possibly 4He and 16O ions). The detector will be composed by a tracker realized with squared scintillating fibres and read out by a dedicated CMOS-based digital SPAD array detector. The first experimental results of a tracker demonstrator are here presented.