Use of short-lived positron emitters for in-beam and real-time β+ range monitoring in proton therapy

• Published in: Physica medica 2020-01, Vol.69, p.248-255
• Main Authors: Bongrand, A., Busato, E., Force, P., Martin, F., Montarou, G.
• Format: Article
• Language: English
• Subjects: [formula omitted] activity distribution; GEANT4 toolkit; Physics; Positron emitters; Proton therapy
• ISSN: 1120-1797; 1724-191X
• DOI: 10.1016/j.ejmp.2019.12.015

•Quantitative estimation of beta + emitters production rates with the GEANT4 simulation toolkit at 55, 65, 120 and 220 MeV.•Comparison of the 55 MeV simulated production rates to data from Dendooven et al.•Comparison of the simulated β+ activity profiles to those extracted from experimental data.•Study of 12N which, from the work of Dendooven et al., is known to be the main isotope for in-beam PET. The purpose of this work is to evaluate the precision with which the GEANT4 toolkit simulates the production of β+ emitters relevant for in-beam and real-time PET in proton therapy. An important evolution in proton therapy is the implementation of in-beam and real-time verification of the range of protons by measuring the correlation between the activity of β+ and dose deposition. For that purpose, it is important that the simulation of the various β+ emitters be sufficiently realistic, in particular for the 12N short-lived emitter that is required for efficient in-beam and real-time monitoring. The GEANT4 toolkit was used to simulate positron emitter production for a proton beam of 55 MeV in a cubic PMMA target and results are compared to experimental data. The three β+ emitters with the highest production rates in the experimental data (11C, 15O and 12N) are also those with the highest production rate in the simulation. Production rates differ by 8% to 174%. For the 12N isotope, the β+ spatial distribution in the simulation shows major deviations from the data. The effect of the long range (of the order of 20 mm) of the β+ originating from 12N is also shown and discussed. At first order, the GEANT4 simulation of the β+ activity presents significant deviations from the data. The need for precise cross-section measurements versus energy below 30 MeV is of first priority in order to evaluate the feasibility of in-beam and real-time PET.