I. Introduction
Hadrontherapy is a cancer treatment technique based on the use of light ion beams under constant expansion and development worldwide [1]. Light ions lose most of their energy at the end of their path accross distances of the order of a few millimeters typically, in the so-called Bragg peak. This is illustrated in the case of protons with an energy of 62 MeV in Fig. 1. This property allows, after proper treatment planning, to increase the ratio between the dose deposited in the tumor and the dose deposited in the surrounding healthy tissues with respect to conventional radiotherapy. Hadrontherapy treatments are however, currently limited by the fact that the range of the ions in patients is not precisely known. Its uncertainty is approximately ±3% of the range [2]–[4]. For example, the uncertainty for protons of 200 MeV (corresponding to a range of approximately 22 cm in patients) is about 6.8 mm.
Energy deposited (dashed-dotted line) and annihilation points (histograms) as a function of the penetration depth for 62 MeV protons on a PMMA target [5]. The points show experimental data from [6].