Measurement of nuclear reaction cross sections by using Cherenkov radiation toward high-precision proton therapy

Monitoring the in vivo dose distribution in proton therapy is desirable for the accurate irradiation of a tumor. Although positron emission tomography (PET) is widely used for confirmation, the obtained distribution of positron emitters produced by the protons does not trace the dose distribution due to the different physical processes. To estimate the accurate dose from the PET image, the cross sections of nuclear reactions that produce positron emitters are important yet far from being sufficient. In this study, we measured the cross sections of ¹⁶O(p,x)¹⁵O, ¹⁶O(p,x)¹³N, and ¹⁶O(p,x)¹¹C with a wide-energy range (approximately 5-70 MeV) by observing the temporal evolution of the Cherenkov radiation emitted from positrons generated via β⁺ decay along the proton path. Furthermore, we implemented the new cross sectional data into a conventional Monte Carlo (MC) simulation, so that a direct comparison was possible with the PET measurement. We confirmed that our MC results showed good agreement with the experimental data, both in terms of the spatial distributions and temporal evolutions. Although this is the first attempt at using the Cherenkov radiation in the measurements of nuclear cross sections, the obtained results suggest the method is convenient and widely applicable for high precision proton therapy.