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In this work, perturbation factors for the PTW 23343 Markus ionization chamber in proton beams were determined using Monte Carlo simulations based on the MCNPX code in version of 2.7.0. The calculations were performed for chosen proton energies from 15 MeV to 80 MeV and for various energy spread. The main conclusion is that the perturbation factors for the considered ionization chamber cannot be neglected in the region with the disturbed proton equilibrium in the above-mentioned energy range.

We present experimental investigation of cross sections for processes crucial in view of prompt-gamma imaging. The prompt-gamma rays were produced from an interaction of a proton beam with different phantom materials composed of carbon, oxygen and hydrogen. The used target setup allowed precise selection of the investigated depth in the phantom. We studied details of the dependence of prompt-gamma yields on beam energy, detection angle and elemental composition of irradiated phantom. The analysis was focused on the discrete transitions with the largest cross sections: 4.44 MeV in 12C and 6.13 MeV in 16O. The results are presented in form of profiles of the prompt-gamma yield as a function of depth. They are compared to calculations including different cross-section models. Obtained results are in agreement with the model exploiting cross-section data collected from the literature, but the comparison with the TALYS model shows discrepancies. In the latest experiment, special attention was paid to the shape of the distal fall-off. The width of that fall-off is directly linked to the resolution of prompt-gamma based methods of range verification. Preliminary results on the beam-energy dependence of this quantity are presented.

Summary Purpose Heavy charged particle therapy beams need to be modified before entering the target in order to deliver the prescribed spatial dose distribution. Small and medium lateral treatment fields are usually formed by a system of scatterers and collimators. A design goal is to mi-nimize the beam-losses in the vicinity of the patient in order to reduce the patient's irradiation by secondary particles while keeping a homo-geneous dose distribution over the treatment field. Materials and methods Track – a Monte Carlo code to calculate beam profiles on the target after passing through a system of scatterers and collimators has been developed. A physical model used in the code is presented. Its approximations and restrictions are discussed. Results Results of simulations are compared with experimental data. Validity of the current physical model is discussed. Conclusions The results are in a good agreement with experimental data.

Acta physica Polonica / B 48(3), 675-678 (2017). doi:10.5506/APhysPolB.48.675, Published by Inst. of Physics, Jagellonian Univ., Cracow