Development of a GAGG prompt gamma camera and simultaneous imaging with prompt X-rays during irradiation by proton beams at clinical dose level

Prompt gamma photon imaging is a promising method for observing a beam's shape and estimating the range of the beam from outside a subject. However 2 dimensional images of prompt gamma photons during irradiation of protons at clinical dose level were still difficult to measure. To achieve prompt gamma photon imaging, we developed a new gamma camera and imaged prompt gamma photons while irradiating proton beams to a phantom at clinical dose level. We also compared the images with simultaneously measured prompt X-ray images. The developed gamma camera uses a 10 mm thick GAGG block optically coupled to a flat panel photomultiplier tube (FP-PMT), and it is contained in a 20 mm thick tungsten container with a pinhole collimator attached. Proton beams at clinical dose level were irradiated to a poly-methyl-methacrylate (PMMA) block, and the gamma camera imaged prompt gamma photons. The prompt X-rays were simultaneously measured during irradiation of proton beams. For all of the tested beams, we could measure the beam shapes of the prompt gamma photons and the prompt X-rays and the ranges could also be estimated from the images. We confirmed that the prompt gamma photon imaging using our developed gamma camera, as well as prompt X-ray imaging, is promising for beam imaging and range estimation in proton therapy at clinical dose level. In the conference, we will also show the time sequential prompt gamma and X-ray images.