Effect of scattering angle on energy loss radiography imaging for various proton energies relevant in proton therapy: A simulation study

Introduction The quality of cancer treatment with protons critically depends on the accurate determination of proton stopping powers (PSPs) of traversed tissues. Nowadays, proton treatment planning is based on stopping powers derived from X-ray Computed Tomography (CT) images leading to systematic uncertainties in the proton range in a patient of 3–4% and even up to 10% in regions containing bone. This may cause no dose in parts of the tumor and overdose in healthy tissues. Purpose In order to reduce the uncertainty in the translation of the X-ray CT image into a map of PSPs, we study proton radiography imaging as it delivers PSPs directly, without using a model. Materials and methods Using the Geant4 toolkit we simulate the proton radiography system with two position sensitive detectors and an energy detector. The imaged object is placed between the position detectors. The energy loss radiographs of the phantom with various, including tissue-like, materials are obtained. The multiple Coulomb scattering of a proton passing through various materials blurs the energy loss radiography image, but selecting protons travelling along almost straight paths decreases the blurring. Results Our simulations show that considering protons with small scattering angles increases sharpness between the material boundaries in the energy loss radiographs, and materials with small density differences are distinguished. Conclusion Proton radiography provides a direct information on PSPs of tissues inside the human body improving the accuracy of the calculation of the dose deposition by protons in a patient. Disclosure Authors have no relevant financial or nonfinancial relationships to disclose.