Characterization of prompt gamma ray emission for in vivo range verification in particle therapy: A simulation study.

In this paper we investigate the emission and detection characteristics of prompt gamma (PG) rays for in vivo range verification during hadron therapy, using Geant4 simulations. Proton, 4He and 12C beams of varying energy are incident on water phantoms. The PG production yield, energy spectral characteristics and spatial correlation with the Bragg Peak (BP) have been quantified. Further, the angular distributions for PG detection with respect to a point-of-reference on the phantom surface have been explored. The temporal properties of PG emission and time-of-flight (TOF) of PG detection have also been investigated in correlation with the changing particle beam range. Our results show that the primary PG rays from nuclear interactions of the primary beam exhibit the closest correlation to the beam range but its signal is significantly masked by the concurrent secondary PG rays, particularly for heavier ions such as carbon ion beams. The PG TOF spectroscopy encodes the essential information of the beam range but requires high time resolution measurements to retrieve it. A hybrid PG detection system to utilize the energy, timing and spatial characteristics of PG rays is desirable for BP tracking in real-time.

Characterization of prompt gamma-ray emission with respect to the Bragg peak for proton beam range verification: A Monte Carlo study.

In this paper we report a Geant4 simulation study to investigate the characteristic prompt gamma (PG) emission in a water phantom for real-time monitoring of the Bragg peak (BP) during proton beam irradiation. The PG production, emission spatial correlation with the BP, and position preference for detection with respect to the BP have been quantified in different PG energy windows as a function of proton pencil-beam energy from 100 to 200MeV. The PG response to small BP shifts was evaluated using a 2cm-thick slab with different human body materials embedded in a water phantom. Our results show that the prominent characteristic PG emissions of 4.44, 5.21 and 6.13MeV exhibit distinctive correlation with the dose deposition curve. The accuracy in BP position identification using these characteristic PG rays is highly consistent as the beam energy increases from 100 to 200MeV. There exists a position preference for PG detection with respect to the BP position, which has a strong dependence on the proton beam energy and PG energies. It was also observed that a submillimeter shift of the BP position can be realized by using PG signals. These results indicate that the characteristic PG signal is sensitive and reliable for BP tracking. Although the maximization of the PG measurement associated with the BP is difficult, it can be optimized with energy and detection position preferences.