TOPAS/Geant4 configuration for ionization chamber calculations in proton beams

Wulff, Jörg; Baumann, Kilian-Simon; Verbeek, Nico; Bäumer, Christian; Timmermann, Beate; Zink, Klemens

doi:10.1088/1361-6560/aac30e

Cited by 32 publications

(89 citation statements)

References 35 publications

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“…For the secondary protons, we observed differences between the spectra generated with the different Monte Carlo codes for energies between 125 and 135 MeV. The production of a secondary proton from an 16 O nucleus requires an energy of $ 12 MeV, 68 ; therefore, the gap between the primary and secondary protons visible in the spectra generated with TOPAS and FLUKA is reasonable. However, this gap cannot be observed in the spectrum generated with PENH.…”

Section: Discussionmentioning

confidence: 90%

“…Table I shows the elemental compositions of water and air used in the Monte Carlo simulations. For all elements, only the main isotopes were considered (e.g., no 17 O but only 16 O in water as well as air). Water had a density of 1.0 g/cm 3 and a mean ionization potential of I w ¼ 78 eV.…”

Section: A Geometries Materials and Source Parametersmentioning

confidence: 99%

“…In the following subsections, the Monte Carlo codes used are described shortly. and prompt-gamma emission are included for a limited number of isotopes: 1 H, 12 C, 14 N, 16 O, 31 P, 40 Ca. 30 Both PENELOPE and PENH have been reported to pass the Fano test within 0.1% 31,33 for the energy range of interest to this work.…”

Section: B Calculated Quantitiesmentioning

confidence: 99%

“…Hence, to provide more data for protons and especially heavier ions, the use of general purpose codes such as fluka and Geant4, primarily designed for high‐energy physics applications, needs to be investigated for the use in ionization chamber calculations. A first study proved that TOPAS, a toolkit based on Geant4, may be used to calculate

f_{Q}

factors in proton beams . On this basis, its usage for the determination of beam quality correction factors in clinical photon and especially proton beams shall be investigated in this work.…”

Section: Introductionmentioning

confidence: 99%

“…A first study proved that TOPAS, a toolkit based on Geant4, may be used to calculate f Q factors in proton beams. 16 On this basis, its usage for the determination of beam quality correction factors in clinical photon and especially proton beams shall be investigated in this work.…”

Section: Introductionmentioning

confidence: 99%

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Comparison of penh, fluka, and Geant4/topas for absorbed dose calculations in air cavities representing ionization chambers in high‐energy photon and proton beams

et al. 2019

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Purpose The purpose of this work is to analyze whether the Monte Carlo codes penh, fluka, and geant4/topas are suitable to calculate absorbed doses and fQ/fQ0 ratios in therapeutic high‐energy photon and proton beams. Methods We used penh, fluka, geant4/topas, and egsnrc to calculate the absorbed dose to water in a reference water cavity and the absorbed dose to air in two air cavities representative of a plane‐parallel and a cylindrical ionization chamber in a 1.25 MeV photon beam and a 150 MeV proton beam — egsnrc was only used for the photon beam calculations. The physics and transport settings in each code were adjusted to simulate the particle transport as detailed as reasonably possible. From these absorbed doses, fQ0 factors, fQ factors, and fQ/fQ0 ratios (which are the basis of Monte Carlo calculated beam quality correction factors kQ,Q0) were calculated and compared between the codes. Additionally, we calculated the spectra of primary particles and secondary electrons in the reference water cavity, as well as the integrated depth–dose curve of 150 MeV protons in water. Results The absorbed doses agreed within 1.4% or better between the individual codes for both the photon and proton simulations. The fQ0 and fQ factors agreed within 0.5% or better for the individual codes for both beam qualities. The resulting fQ/fQ0 ratios for 150 MeV protons agreed within 0.7% or better. For the 1.25 MeV photon beam, the spectra of photons and secondary electrons agreed almost perfectly. For the 150 MeV proton simulation, we observed differences in the spectra of secondary protons whereas the spectra of primary protons and low‐energy delta electrons also agreed almost perfectly. The first 2 mm of the entrance channel of the 150 MeV proton Bragg curve agreed almost perfectly while for greater depths, the differences in the integrated dose were up to 1.5%. Conclusion penh, fluka, and geant4/topas are capable of calculating beam quality correction factors in proton beams. The differences in the fQ0 and fQ factors between the codes are 0.5% at maximum. The differences in the fQ/fQ0 ratios are 0.7% at maximum.

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Section: Discussionmentioning

confidence: 90%

Section: A Geometries Materials and Source Parametersmentioning

confidence: 99%

Section: B Calculated Quantitiesmentioning

confidence: 99%

f_{Q}

factors in proton beams . On this basis, its usage for the determination of beam quality correction factors in clinical photon and especially proton beams shall be investigated in this work.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Comparison of penh, fluka, and Geant4/topas for absorbed dose calculations in air cavities representing ionization chambers in high‐energy photon and proton beams

et al. 2019

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The influence of nuclear interactions on ionization chamber perturbation factors in proton beams: FLUKA simulations supported by a Fano test

et al. 2018

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Purpose In all recent protocols for the reference dosimetry of clinical proton beams, ionization chamber perturbation factors are assumed to be unity. In this work, such factors were computed using the FLUKA Monte Carlo code for three ionization chamber types, with particular attention to the influence of nuclear interactions. Methods The accuracy of the transport algorithms implemented in FLUKA was first evaluated by performing a Fano cavity test. Ionization chamber perturbation factors were computed for the PTW‐34001 Roos® and the PTW‐34070 and PTW‐34073 Bragg peak® chambers for proton beams of 60–250 MeV using the same transport parameters that were needed to pass the Fano test. Results FLUKA was found to pass the Fano test within 0.15%. Ionization chamber simulation results show that the presence of the air cavity and the wall results in dose perturbations of the order of 0.6% and 0.8%, respectively. The 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. Conclusion Ionization chamber perturbations can amount to 1% in high‐energy proton beams and therefore need to be considered in dosimetry procedures.

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Determination of surface dose in pencil beam scanning proton therapy

et al. 2020

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Purpose/objective Quantification of surface dose within the first few hundred water equivalent µm is challenging. Nevertheless, it is of large interest for the proton therapy community to study dose effects in the skin. The experimental determination is affected by the detector properties, such as the detector volume and material. The International Commission on Radiation Units and Measurements in its report 39 recommends assessing the skin dose at a depth of 0.07 mm. The aim of this study is the estimation of the absorbed dose at and around a depth of 70 µm. We used various dosimetric approaches in conjunction with proton pencil beam scanning delivery to determine the skin dose in a clinical setting. Material/methods Five different detectors were tested for determining the surface dose in water: EBT3 and HD‐V2 GAFCHROMIC™ radiochromic film, LiF:Mg,Ti thermoluminescent dosimeter, IBA PPC05 plane‐parallel ionization chamber, and PTW 23391 extrapolation chamber. The irradiation setup consisted of quasi‐monoenergetic scanned proton pencil beams with kinetic energies of 100, 150, and 226.7 MeV, respectively. Radiochromic films were placed within a vertical stack and in wedge geometry and were analyzed with FilmQA Pro™ adopting triple channel dosimetry. The extrapolation chamber PTW 23391, which served as a reference in the current work, was used in a conventional ionization chamber setup with a fixed electrode gap of 2 mm. Three Kapton® entrance windows with thicknesses of 25, 50, and 75 µm were employed. Thermoluminescent dosimeters were provided as powder and were pressed onto a sheet of aluminum. Furthermore, the Monte Carlo code TOol for PArticle Simulation (TOPAS) in version 3.1.p2 was used to model an IBA pencil beam scanning nozzle and score dose to water in a water phantom. Results The resulting depth dose curves were normalized to their 100% dose at the reference depth of 3 cm. We obtained the skin doses with the extrapolation chamber and with TOPAS. For the experimental approach this resulted in 79.7 ± 0.3%, 86.0 ± 0.6%, and 87.1 ± 0.1% for the proton energies 100, 150, and 226.7 MeV, respectively. The results for TOPAS were 80.1 ± 0.2% (100 MeV), 87.1 ± 0.5% (150 MeV), and 86.9 ± 0.4% (226.7 MeV), respectively. Based on the experimental results of the skin dose, we provided a clinically relevant surface extrapolation factor for the common measurement methods. This allows the result of the first measurement depth of a detector to be scaled to the dose at the skin depth. Most practical would be the use of the surface extrapolation factor for the PPC05 chamber, due to its direct reading, the wide availability in clinics and the low uncertainties. The calculated factors were 0.986 ± 0.004 for 100 MeV, 0.961 ± 0.008 for 150 MeV, and 0.963 ± 0.003 for 226.7 MeV. Conclusions In this study, dissimilar experimental approaches were evaluated with respect to measurements at depths close to the surface. The experimental depth dose curves are in good agreement with the simulation with TOPAS Monte Carlo. To the author's...

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TOPAS/Geant4 configuration for ionization chamber calculations in proton beams

Cited by 32 publications

References 35 publications

Comparison of penh, fluka, and Geant4/topas for absorbed dose calculations in air cavities representing ionization chambers in high‐energy photon and proton beams

Comparison of penh, fluka, and Geant4/topas for absorbed dose calculations in air cavities representing ionization chambers in high‐energy photon and proton beams

The influence of nuclear interactions on ionization chamber perturbation factors in proton beams: FLUKA simulations supported by a Fano test

Determination of surface dose in pencil beam scanning proton therapy

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