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

Objective . Proton therapy currently faces challenges from clinical complications on organs-at-risk due to range uncertainties. To address this issue, positron emission tomography (PET) of the proton-induced 11 C and 15 O activity has been used to provide feedback on the proton range. However, this approach is not instantaneous due to the relatively long half-lives of these nuclides. An alternative nuclide, 12 N (half-life 11 ms), shows promise for real-time in vivo proton range verification. Development of 12 N imaging requires better knowledge of its production reaction cross section. Approach . The 12 C(p,n) 12 N 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 × 10 8 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 12 N 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, a comparison between measured and simulated scanner sensitivity showed a scaling factor of 1.25 (±3%). Despite this, there was an improvement in the precision of the cross section measurement compared to values reported by the only previous study. Significance . Short-lived 12 N imaging is promising for real-time in vivo verification of the proton range to reduce clinical complications in proton therapy. The verification procedure requires experimental knowledge of the 12 N production cross section for proton energies of clinical importance, to be incorporated in a Monte Carlo framework for 12 N imaging prediction. This study is the first to achieve a precise measurement of the 12 C(p,n) 12 N nuclear cross section for such proton energies.