Experimental performance of double-scattering Compton camera with anthropomorphic phantom

In proton therapy, it is important to very accurately determine the range of the proton beam. Recently it was found that this range can be determined from the distribution of the prompt gammas generated along the beam's passage. The Compton imaging technique can be considered to be a promising candidate for accurate determination of prompt gamma distributions, in that it produces a better image for higher-energy gammas when compared with conventional mechanical-collimation-type imagers. In the present study, the Compton imaging technique was evaluated by experimentally obtaining Compton images of relatively high-energy gamma sources positioned in an anthropomorphic phantom. Preparatory to that, two point-like gamma sources, ¹³⁷Cs (662 keV) and ²²Na (1275 keV), were placed in the brain region of the phantom at different depths and imaged using a double-scattering Compton camera. The Compton camera, recently developed as a prototype system, consists of two position-sensitive semiconductor detectors as scatterer detectors and a scintillation detector as an absorber detector. The evaluated imaging and angular resolutions for the source energies of 662 and 1275 keV were 13.7 mm and 5.9° FWHM and 11.4 mm and 3.8° FWHM, respectively.