Experimental study for the production cross section of β+ emitters for range verification in protontherapy

Abstract

In protontherapy, the uncertainties in the range of the beam delivered to the patient result in some safety margins in the planning that limit the dose that can be delivered to the tumour. For this reason, there is an intensive research program aiming at in vivo range verification. In particular, positron emitters are induced on C, N, O, Ca and P nuclei by the protons of the beam in the patient. Based on this, in vivo PET range verification relies on the comparison of measured and simulated activity distributions of these isotopes. The accuracy of the simulated distribution depends on the accuracy of the cross section for the production of these positron emitters. A revision of the experimental data available in the EXFOR database shows that the corresponding cross sections do not always cover the full energy range of interest, and that there are sizeable differences between the different measurements. The aim of this study is to develop a method for measuring the production cross sections of the positron emitters 11C and 13N in the most abundant isotopes in human body: C, N and O. This will be used, in a first step, to measure the cross section of positron emitters produced by a low energy proton beam at the CNA cyclotron. The 18 MeV energy beam produced by the cyclotron is degraded using a multi-stack target configuration in order to obtain the cross section in different energy points. The activity induced by the beam has been measured using a clinical PET scanner. The production cross section of these reaction channels have been measured and compared with the available data, showing a reasonable agreement with them within uncertainties.