Determination of distal dose edge location by measuring right-angled prompt-gamma rays from a 38 MeV proton beam

In clinical applications, it is very important to accurately determine the range of a proton beam in a patient. Recently, a prototype prompt-gamma scanning system, called a prompt-gamma scanner (PGS), has been constructed at Hanyang University in Korea with the collaboration of the Korean national cancer center (NCC), based on a series of Monte Carlo simulations. The PGS system is composed of a prompt-gamma collimator, a CsI(Tl) scintillation detector, a multi-channel analyzer (MCA), a precision movement system, and an integrated readout system. The prompt-gamma collimator is designed to effectively shield high-energy neutrons from the proton beam passage and subsequent capture gammas. The PGS system can be used to scan the distribution of the prompt gammas in the patient from the proton beam passage. The distribution of the prompt gammas can then be used to determine the proton beam range or the distal dose edge in the patient. In this study, the PGS system was tested with a 38 MeV proton beam at the Korea cancer center hospital (KCCH). The experiment was also simulated, using a Monte Carlo particle transport simulation code, MCNPX. Our result is very encouraging, showing that there is a clear correlation between the distribution of the prompt gammas and the location of the distal dose edge for the 38 MeV proton beam. According to our result, we believe that the location of the distal dose edge can be determined within 1-2 mm from the distribution of the prompt gammas.