Proton range monitoring using 13N peak for proton therapy applications

Abstract

The Monte Carlo method is employed in this study to simulate the proton irradiation of a water-gel phantom. Positron-emitting radionuclides such as 11C, 15O, and 13N are scored using the Particle and Heavy Ion Transport Code System Monte Carlo code package. Previously, it was reported that as a result of 16O(p,2p2n)13N nuclear reaction, whose threshold energy is relatively low (5.660 MeV), a 13N peak is formed near the actual Bragg peak. Considering the generated 13N peak, we obtain offset distance values between the 13N peak and the actual Bragg peak for various incident proton energies ranging from 45 to 250 MeV, with an energy interval of 5 MeV. The offset distances fluctuate between 1.0 and 2.0 mm. For example, the offset distances between the 13N peak and the Bragg peak are 2.0, 2.0, and 1.0 mm for incident proton energies of 80, 160, and 240 MeV, respectively. These slight fluctuations for different incident proton energies are due to the relatively stable energy-dependent cross-section data for the 16O(p,2p2n)13N nuclear reaction. Hence, we develop an open-source computer program that performs linear and non-linear interpolations of offset distance data against the incident proton energy, which further reduces the energy interval from 5 to 0.1 MeV. In addition, we perform spectral analysis to reconstruct the 13N Bragg peak, and the results are consistent with those predicted from Monte Carlo computations. Hence, the results are used to generate three-dimensional scatter plots of the 13N radionuclide distribution in the modeled phantom. The obtained results and the developed methodologies will facilitate future investigations into proton range monitoring for therapeutic applications.

A Feasibility Study on Proton Range Monitoring Using 13N Peak in Inhomogeneous Targets

“…The obtained offset value is in a good agreement with our previous work on irradiation of homogeneous phantoms [ 18 ]. For the SOBP proton beam results shown in Figure 4 b, the 13N peak is within the same ~1 to ~2 mm offset distance that we have previously reported [ 18 ]. However, since the SOBP is broad, the 13 N peak would be inside the SOBP region, see Figure 4 b. Interestingly, the generated 13 N peak in the SOBP region (see Figure 4 b) is broader than that of pristine Bragg peak (see Figure 4 a), mainly due to the proton beam energy modulation that was used to achieve a spread-out Bragg peak.…”

“…Comparing the offset distance between the Bragg peak and the 13 N peak, an offset distance of ~1 mm was obtained for both peaks shown in Figure 4 a. The obtained offset value is in a good agreement with our previous work on irradiation of homogeneous phantoms [ 18 ]. For the SOBP proton beam results shown in Figure 4 b, the 13N peak is within the same ~1 to ~2 mm offset distance that we have previously reported [ 18 ].…”

“…Similar to our previous works on homogeneous targets [ 18 , 19 ], we have employed our previously developed SA technique to quantify the amount of produced 15 O, 11 C, and 13 N positron emitting radionuclides in the modelled target phantoms. The SA was initially developed for kinetic analysis of PET tracer [ 23 ].…”

“…Considering the low threshold and rather substantial yield of 13 N producing nuclear reaction, it was found to be useful for proton range monitoring and verification [ 17 ]. Previously, we have investigated the use of this nuclear reaction and the generated 13 N peak for proton range monitoring and verification in homogeneous targets both numerically [ 18 ] and experimentally [ 19 ]. In our previous works, we have also developed a spectral analysis (SA) approach to detect 13 N production from dynamic PET data and succeeded in rendering 13 N distribution proximal to the Bragg peak in homogenous phantom targets.…”

“…In the present work, we have extended our previously developed tools [ 18 , 19 ] for investigating the feasibility of using 13 N for proton range monitoring and verification in inhomogeneous target phantoms. The Particle and Heavy Ion Transport code System (PHITS) ( (accessed on 14 September 2022)) Monte Carlo (MC) package was used.…”