Dose build-up effects induced by delta electrons and target fragments in proton Bragg curves - measurements and simulations.

Dose build-up effects induced by delta electrons and target fragments in proton Bragg curves - measurements and simulations.
Phys Med Biol. 2018 Aug 08;:
Authors: Pfuhl T, Horst F, Schuy C, Weber U
Abstract
Dose build-up effects in the entrance channel of proton Bragg curves were investigated in detail by means of simulations and experiments. There are two relevant dose build-up effects. Firstly, the δ-electron build-up effect which takes place in the first few millimeters of the tissue until an equilibrium state of the forwards scattered δ-electrons is reached. Secondly, the target fragment build-up effect that covers the first centimeters in the entrance channel of the proton Bragg curve. These target fragments are created in inelastic interactions of the beam protons with the target nuclei and partially have low kinetic energies and/or high atomic numbers compared to the incident beam protons. Consequently, the target fragments possess high LET values and thus an increased RBE. However, the production cross sections relevant for target fragmentation in ion beam therapy still have large uncertainties. Therefore, in this work target fragmentation was investigated indirectly by measuring low-noise proton Bragg curves with the focus placed on their build-up regions. The measurements clearly show the magnitude and shape of the two different build-up effects. Additionally, with the application of a magnetic filter, it was possible to ...

Source: Physics in Medicine and Biology - August 8, 2018 Category: Physics Authors: Pfuhl T, Horst F, Schuy C, Weber U Tags: Phys Med Biol Source Type: research