Purpose. To provide Monte Carlo calculated beam quality correction factors (k Q ) for monoenergetic proton beams using the Monte Carlo code fluka. Materials and methods. The Monte Carlo code fluka was used to calculate the dose absorbed in a water-filled reference volume and the air-filled cavities of six plane-parallel and four cylindrical ionization chambers. The chambers were positioned at the entrance region of monoenergetic proton beams with energies between 60 and 250 MeV. Based on these dose values, f Q as well as k Q factors were calculated while factors were taken from Andreo et al (2020 Phys. Med. Biol. 65 095011). Results. k Q factors calculated in this work were found to agree with experimentally determined k Q factors on the 1%-level, with only two exceptions with deviations of 1.4% and 1.9%. The comparison of f Q factors calculated using fluka with f Q factors calculated using the Monte Carlo codes geant4 and penh showed a general good agreement for low energies, while differences for higher energies were pronounced. For high energies, in most cases the Monte Carlo codes fluka and geant4 lead to comparable results while the f Q factors calculated with penh are larger. Conclusion. fluka can be used to calculate k Q factors in clinical proton beams. The divergence of Monte Carlo calculated k Q factors for high energies suggests that the role of nuclear interaction models implemented in the different Monte Carlo codes needs to be investigated in more detail.

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In particle therapy of lung tumors, modulating effects on the particle beam may occur due to the microscopic structure of the lung tissue. These effects are caused by the heterogeneous nature of the lung tissue and cannot be completely taken into account during treatment planning, because these micro structures are too small to be fully resolved in the planning CT. In several publications, a new material parameter called modulation power (P mod ) was introduced to characterize the effect. For various artificial lung surrogates, this parameter was measured and published by other groups and ranges up to approximately 1000 µm. Studies investigating the influence of the modulation power on the dose distribution during irradiation are using this parameter in the rang of 100 to 800 µm. More precise measurements for P mod on real lung tissue have not yet been published. In this work, the modulation power of real lung tissue was measured using porcine lungs in order to produce more reliable data of P mod for real lung tissue. For this purpose, ex-vivo porcine lungs were frozen in a ventilated state and measurements in a carbon ion beam were performed. Due to the way the lungs were prepared and transferred to a solid state, the lung structures that modulate the beam could also be examined in detail using micro CT imaging. An optimization of the established methods of measuring the modulation power, which takes better account of the typical structures within lung tissue, was developed as well.

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