Determination of the Distal Dose Edge in the Human Voxel Model by Measuring the Prompt Gamma Distribution in Proton Therapy: A Monte Carlo study

Abstract

In vivo dose (particularly the distal dose edge) verification in proton therapy is very important for the safety of patients and for the successful treatment. It was demonstrated that the distal dose edge in the proton doe distribution can be determined by measuring the distribution of the prompt gammas generated by the proton-induced nuclear interaction along the proton passage in water phantom. For the clinical application of the technique determining the distal dose edge, the prompt gammas generated from the elements consisting of the human body should be considered. In the present study, the human voxel model was developed with the computed tomography data of the ATOM adult female phantom which is formulated based on the approximately body composition. The MCNPX code was used to analyze the energy spectra and the generating distribution of the prompt gammas from the major elements composing the human voxel model. And then, the prompt gamma distribution, generated from the human voxel model and measured by the array-type prompt gamma detection system, was calculated and compared with the proton dose distribution in the human voxel model. Our results show that the organs including the higher rate of oxygen could emit the more prompt gammas within the energy window of 4-10 MeV, compare to the other elements in the human body. A good agreement was found between the location of the distal dose edge in the human voxel model and the distribution of the prompt gammas measured by the detection system, despite the significant background gammas by mainly the neutron capture gammas.