Range and density variations monitoring during proton therapy based on time-of-flight detection of prompt gamma radiation

The aim of this work is to seek for an optimal angular detection of prompt photons emitted perpendicularly to the beam direction using a time-of-flight technique, which enables a huge neutron background rejection. A homogeneous PMMA phantom was studied. The prompt photon profile correlates well with the dose distal fall-off when the proper selection of θ=90±0.7° of the emitted prompt gamma rays is made. The correlation to the dose can be detected with the present method with an accuracy of up to 4 mm at 50% height of the prompt gamma rays profile.