Proton imaging at the end of the proton range

Abstract

Since the earliest studies on the usage of protons for image production, it was declared that to take advantage of proton beam it is necessary to choose an initial proton energy close to the minimum possible value, i.e., to work at the end of the proton range, where the proton flux changes very steeply. However, this idea was declared, but was not investigated. In the present work, we study the efficiency of image production at the end of the proton range with the three physical observables that can be used for such purpose: the mean energy of exit proton, number of protons and total energy of exit protons. By using a Monte Carlo simulation, we studied the uncertainties in the determination of object thickness with these observables at the conditions typical for medical imaging. At the area before the end of the proton range, the uncertainty in thickness determination obtained analysing the mean energy of exit proton is significantly less than the uncertainty obtained for the number of protons. At the end of the range, the number of protons becomes preferable for the measurement of the absorber thickness. The precision of the total energy of exit protons matches the precision of the number of protons at the end of the range and the precision of the mean energy of exit proton outside this region. Any effect that justifies the idea to work at the end of the proton range was not observed.