Measurement of the ¹²C(p,n)¹²N reaction cross section below 150 MeV

Abstract

Objective: Proton therapy currently faces challenges from clinical complications on organs-at-risk due to range uncertainties, anatomical changes, and setup errors. To address this issue, Positron Emission Tomography (PET) of the proton-induced 11C and 15O activity has been used to provide feedback on the proton range. However, this approach is not instantaneous due to the long half-lives of these nuclides. An alternative nuclide, 12N (half-life 11 ms), shows promise for real-time in vivo verification of the proton range. Development of 12N imaging requires better knowledge of its production reaction cross section.
Approach: The 12C(p,n)12N reaction cross section was measured by detecting positron activity of graphite targets irradiated with 66.5, 120, and 150 MeV protons. A pulsed beam delivery with 0.7-2×108 protons per pulse was used. The positron activity was measured during the beam-off periods using a dual-head Siemens Biograph mCT PET scanner. The 12N production was determined from activity time histograms.
Main results: The cross section was calculated for 11 energies, ranging from 23.5 to 147 MeV, using information on the experimental setup and beam delivery. Through a comprehensive uncertainty propagation analysis, a statistical uncertainty of 2.6-5.8% and a systematic uncertainty of 3.3-4.6% were achieved. Additionally, calibration measurements showed a systematic correction factor of 1.21 (± 7.5%), which contributed the most to global uncertainty. Despite this, there was an improvement in the precision of the cross section measurement compared to values reported by the only previous study for this nuclear reaction. To obtain a continuous cross section function, a weighted spline interpolation using both datasets was performed.
Significance: Our results were incorporated into the RayStation Monte Carlo (MC) engine for calculating the 12N positron annihilation distribution during treatment, with the aim of developing an MC simulation framework to predict 12N PET imaging for range verification purposes.