Abstract
The novel proton radiography imaging technique has a large potential to be used in direct measurement of the proton energy loss (proton stopping power, PSP) in various tissues in the patient. The uncertainty of PSPs, currently obtained from translation of X-ray Computed Tomography (xCT) images, should be minimized from 3–5% or higher to less than 1%, to make the treatment plan with proton beams more accurate, and thereby better treatment for the patient. With Geant4 we simulated a proton radiography detection system with two position-sensitive and residual energy detectors. A complex phantom filled with various materials (including tissue surrogates), was placed between the position sensitive detectors. The phantom was irradiated with 150 MeV protons and the energy loss radiograph and scattering angles were studied. Protons passing through different materials in the phantom lose energy, which was used to create a radiography image of the phantom. The multiple Coulomb scattering of a proton traversing different materials causes blurring of the image. To improve image quality and material identification in the phantom, we selected protons with small scattering angles. A good quality proton radiography image, in which various materials can be recognized accurately, and in combination with xCT can lead to more accurate relative stopping powers predictions.
Highlights
We applied various cuts on a proton scattering angle to minimize the blurring in the energy loss radiography image, discussed
In this paper we present the analysis of the influence of proton scattering angles on the quality of proton energy loss radiography images for a larger and more complex phantom with 11 materials, including some tissue surrogates
The results at proton beam energy of Ep = 150 MeV show that selecting protons that scattered up to 8.7 mrad give the sharpest edges in the energy loss radiograph, in which different materials can be recognized accurately, but at a cost of statistics
Summary
In the simulations we used the Geant4.9.6p04 version with the standard electromagnetic physics, G4EmStandardPhysics_option3(). The default value of the finalRange parameter, which is included in the standard electromagnetic physics, describes the range for the final step and is used in the computation of the step limit by the ionization process. The scattering of a particle after a given step is simulated, and the path length correction and the lateral displacement are computed. Any energy loss process in Geant must calculate the continuous and discrete energy loss in a material. A given energy threshold, which for secondary electrons varies between 55 keV and 250 keV in the materials used, the energy loss is continuous and above it the energy loss is simulated by the explicit production of secondary particles (gammas, e− and e+)
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