Cross section measurements for production of positron emitters for PET imaging in carbon therapy

In light ion beam therapy, positron (${\beta }^{+}$) emitters are produced by the tissue nuclei through nuclear interactions with the beam ions. They can be used for the verification of the delivered dose using positron emission tomography by comparing the spatial distribution of the ${\beta }^{+}$ emitters activity to a computer simulation taking into account the patient morphology and the treatment plan. However, the accuracy of the simulation greatly depends on the method used to generate the nuclear interactions producing these emitters. In the case of Monte Carlo (MC) simulations, the nuclear interaction models still lack the required accuracy due to insufficient experimental cross section data. This is particularly true for carbon therapy where literature data on fragmentation cross sections of a carbon beam with targets of medical interest are very scarce. Therefore, we performed at GANIL in July 2016 measurements on ${\beta }^{+}$ emitter production cross sections with a carbon beam at 25, 50, and 95 MeV/nucleon on thin targets (C, N, O, and PMMA). We extracted the production cross section of ${}^{10,11}\mathrm{C}, {}^{13}\mathrm{N}$, and ${}^{14,15}\mathrm{O}$ that are essential to constrain or develop MC nuclear fragmentation models.

Figure 1

Experimental set-up showing the different apparatus used for the measurement of the production cross sections of several ${\beta }^{+}$ emitters produced by a carbon beam on different targets.

Figure 2

Example of the collected charges in DOSION over time (solid black line) and the first derivative (dashed red line) to extract the start and end times ($t_{\mathrm{start}}$ and $t_{\mathrm{end}}$) of the irradiation as well as the irradiation time, $t_{\mathrm{irr}}$.

Figure 3

Mechanical drawing of the $\gamma$ detection system.

Figure 4

Spectra of the number of 511 keV $\gamma$ rays detected in coincidence per second for (a) the graphite and (b) the PMMA target with a 94.3 MeV/nucleon ${}^{12}\mathrm{C}$ beam. The insets show close-up views on the short decay times. The total fit as well as the contributions of the individual nuclides included are shown.

Figure 5

Production cross sections of ${\beta }^{+}$ emitters extracted for (a) the carbon, (b) the boron nitride targets as well as (c) the reconstructed oxygen target at three beam energies. The given error bars on the energy represent the entrance and exit energy of the beam. For the boron nitride target, the ${}^{10}\mathrm{C}$ and ${}^{11}\mathrm{C}$ have the contributions of both boron and nitrogen target nuclei.