Simulation studies on the correlation of distal dose Fa 11 off of a 70-MeV proton beam with a prompt gamma distribution

While a proton beam has an advantage over conventional electron and photon radiation therapy by sparing healthy tissues and organs surrounding the tumor volume, it is important to know the proton dose distribution, especially the location of distal dose falloff, to ensure the patient's safety and the effectiveness of the treatments. This study is aimed at developing a prompt gamma scanning system by using a Monte Carlo technique for a 70-MeV proton beam, which is a usual low-energy bound of the therapy beam and at designing a system as compact as possible for actual construction. The system is set to measure the distribution of prompt gammas emitted at 90 ± 1° relative to the incident proton beam. The simulation showed that the distal falloff position of the proton beam could be determined from the prompt gamma distribution to an accuracy of 1 - 2 mm.