Use of short-lived positron emitters for in-beam and real-time $\beta^+$ range monitoring in proton therapy
Résumé
Aim: 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.
Background: 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.
Methods: 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.
Results: 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.
Conclusions: 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