Monte Carlo calculation of beam quality correction factors in proton beams using TOPAS/GEANT4 | Semantic Scholar (2024)

FLUKA can be used to calculate Monte Carlo calculated beam quality correction factorskQ for monoenergetic proton beams using the Monte Carlo code FLUKA and shows a general good agreement for low energies, while differences for higher energies were pronounced.

The perturbation factors p Q were shown to deviate from unity for the investigated chambers, contradicting the assumptions made in dosimetry protocols and the approximation of ionization chamber perturbations in proton beams by the respective water-to-air mass stopping power ratio shall be revised.

There is a need for updating the current recommendations, which assume a constant P of unity in carbon-ion beams, to recommendations that consider chamber-induced differences, as shown in the results.

Analysis of currently available data on beam quality correction factors, kQ, for ionization chambers in clinical proton beams and derive their current best estimates for the updated recommendations of the IAEA TRS-398 Code of Practice showed that except for the beam quality dependence of the water-to-air mass stopping power ratio and of the displacement correction factor, there is no remaining beam quality Dependency pQ.

The precise measurement of beam quality correction factors for mono-energy proton beams using the Monte Carlo technique is required in future studies.

The results indicate that PHITS can calculate the [Formula: see text] and [Formula: see text] with high precision and compare with that of a previous study, which was calculated using other Monte Carlo codes under similar conditions.

The k Q values determined in the present work have been compared with the values tabulated in TRS-398 and its forthcoming update and also with those obtained in previous water calorimetric measurements and Monte Carlo calculations and all results were found to agree within the combined uncertainties of the different data.

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The results of this work seem to indicate that the simulation of proton nuclear interactions should be included in the MC calculation of factors in proton beams, perturbation factors in Proton beams should not be neglected, and the detailed MC simulation of ionization chambers allows for an accurate and precise calculation of Factors in clinical protonbeam beams.

It is concluded that perturbation correction factors in proton beams—currently assumed to be equal to unity—are in fact significantly different from unity for some of the ionization chambers studied.

It is now possible to calculate kQ directly using Monte Carlo simulations and results for most ionization chambers give results which are comparable to TG-51 values.

The beam quality correction factors obtained with the complete Clinac geometries and with the monoenergetic beams differ significantly for energies above 12 MeV, which can be ascribed to secondary photons produced in the linac head and the air path towards the phantom.

Whether the Monte Carlo codes penh, fluka, and geant4/topas are capable of calculating beam quality correction factors in proton beams is analyzed.

Ionization chamber perturbation factors are shown to be energy dependent and nuclear interactions must be taken into account for accurate calculation of the ionization chamber's response and need to be considered in dosimetry procedures.

Based on the Fano cavity test, the Geant4/TOPAS Monte Carlo code, in its investigated version, can provide reliable results for IC calculations.

The calculations have been carried out using three different 60Co source models: a monoenergetic point source, a point source with a realistic 60Co spectrum and the simulated phase space from a radiotherapy 60Co unit, showing the possibility of adopting the mean value of the three source models, weighted with the inverse of their corresponding uncertainties, as a better estimate of fc,Qo.

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