Abstract
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.
Highlights
Proton therapy is one of several radiation therapies to treat cancer
The physical processes that produce positron emitters via the nuclear reactions is different from the energy loss process of protons through the electromagnetic interaction; as a result, the positron emission tomography (PET) image does not reflect the dose information along the proton path
The current database of such nuclear reactions is insufficient below 250 MeV, which are important for proton therapy[6,7,8,10,11,14,23,24]
Summary
Note that the acquired cross section and archival data peaked at almost same energy, 35 MeV. In the energy range over 40 MeV, our acquired cross section values gradually decreased This trend was more significant compared to that observed by Akagi et al, Albouy et al, and Valentin. Our acquired cross section values for 10–20 MeV have uncertainties of a few MeV due to the straggling effect, and the typical width of the nuclear resonance line was several hundred keV; narrow peaks formed by the excitation energies were not separated in our data. Our MC simulation results at each time interval were in good agreement with the PET measurements, within 1-σ uncertainty, for all regions This result validates the normalization method and the obtained cross section values of 16O(p,x)15O, 16O(p,x)13N, and 16O(p,x)11C. We conclude that our acquired cross sections are promising choice for realizing the proton dose estimation from the PET images
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