A new method to reconstruct in 3D the emission position of the prompt gamma rays following proton beam irradiation

Abstract

A new technique for range verification in proton beam therapy has been developed. It is based on the detection of the prompt ? rays that are emitted naturally during the delivery of the treatment. A spectrometer comprising 16 LaBr3(Ce) detectors in a symmetrical configuration is employed to record the prompt ? rays emitted along the proton path. An algorithm has been developed that takes as inputs the LaBr3(Ce) detector signals and reconstructs the maximum ?-ray intensity peak position, in full 3 dimensions. For a spectrometer radius of 8?cm, which could accommodate a paediatric head and neck case, the prompt ?-ray origin can be determined from the width of the detected peak with a ? of 4.17?mm for a 180?MeV proton beam impinging a water phantom. For spectrometer radii of 15 and 25?cm to accommodate larger volumes this value increases to 5.65 and 6.36?mm. For a 8?cm radius, with a 5 and 10?mm undershoot, the ? is 4.31 and 5.47?mm. These uncertainties are comparable to the range uncertainties incorporated in treatment planning. This work represents the first step towards a new accurate, real-time, 3D range verification device for spot-scanning proton beam therapy.