Hodoscope coincidence imaging for hadron therapy using a compton camera

In hadron therapy particulate radiation is used to treat regions in close proximity to vital organs or tissue. Protons, or Carbon ions, provide enhanced treatment due to the characteristic Bragg peak structure of dose deposition, which constrains maximum dose deposition to a small volume of the patient. However, as there is no transmitted beam novel methods of beam monitoring must be developed to ensure accuracy in dose delivery. The particulate beam activates the target material giving rise to positrons, prompt gamma-rays and neutrons. While positron emission imaging is possible, Compton imaging has some distinct advantages in this role. The broad spectrum of prompt radiation means that incident photon energy is unknown. Unless incident photon energy can be determined, Compton imaging requires that either three or more interactions be measured or that the photon spectrum also be estimated during image reconstruction. However, the extension of the image space to include incident energy is inconvenient as the image space dimension is increased. Here pencil-beam therapy is considered, which allows the inclusion of beam information into the reconstruction algorithm. Coincident hodoscope information constrains the unknown spatial distribution of the emission field to a single dimension leaving one spatial and one spectral dimension. In this investigation hodoscope coincidence imaging using a Compton camera was explored using data simulated with GEANT4 and was shown to be a promising approach to the challenge of monitoring in hadron therapy.