Experiments and Monte Carlo simulations on multiple Coulomb scattering of protons

Verbeek, Nico; Wulff, Jörg; Janson, Martin S.; Bäumer, Christian; Zahid, Sameera; Timmermann, Beate; Brualla, L.

doi:10.1002/mp.14860

Cited by 6 publications

(6 citation statements)

References 39 publications

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“…TOPAS was chosen in this study, as it is capable of calculating the dose distribution, including the aura consisting of neutrons and gammas ( 25 , 35 ). Moreover, it was shown that TOPAS is able to simulate multiple Coulomb scattering in the lucite RS used in the present work with sufficient accuracy ( 26 ). As a first verification step of the MC framework, the in-field dose distribution was compared to RayStation, showing an excellent agreement in the 3D global gamma test as shown in Figure 3 .…”

Section: Discussionmentioning

confidence: 83%

“…The protons started 50 cm upstream of the isocenter at the nozzle exit of the treatment head. The Fermi–Eyges parameters were back-projected in vacuum to the nozzle exit ( 24 – 26 ). The method of ( 27 ) was applied to obtain the spot positions of the protons, taking into account the deflection of the protons at the two foci from the scanning magnets of the pencil beam dedicated nozzle.…”

Section: Methodsmentioning

confidence: 99%

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Validation of a Monte Carlo Framework for Out-of-Field Dose Calculations in Proton Therapy

et al. 2022

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Proton therapy enables to deliver highly conformed dose distributions owing to the characteristic Bragg peak and the finite range of protons. However, during proton therapy, secondary neutrons are created, which can travel long distances and deposit dose in out-of-field volumes. This out-of-field absorbed dose needs to be considered for radiation-induced secondary cancers, which are particularly relevant in the case of pediatric treatments. Unfortunately, no method exists in clinics for the computation of the out-of-field dose distributions in proton therapy. To help overcome this limitation, a computational tool has been developed based on the Monte Carlo code TOPAS. The purpose of this work is to evaluate the accuracy of this tool in comparison to experimental data obtained from an anthropomorphic phantom irradiation. An anthropomorphic phantom of a 5-year-old child (ATOM, CIRS) was irradiated for a brain tumor treatment in an IBA Proteus Plus facility using a pencil beam dedicated nozzle. The treatment consisted of three pencil beam scanning fields employing a lucite range shifter. Proton energies ranged from 100 to 165 MeV. A median dose of 50.4 Gy(RBE) with 1.8 Gy(RBE) per fraction was prescribed to the initial planning target volume (PTV), which was located in the cerebellum. Thermoluminescent detectors (TLDs), namely, Li-7-enriched LiF : Mg, Ti (MTS-7) type, were used to detect gamma radiation, which is produced by nuclear reactions, and secondary as well as recoil protons created out-of-field by secondary neutrons. Li-6-enriched LiF : Mg,Cu,P (MCP-6) was combined with Li-7-enriched MCP-7 to measure thermal neutrons. TLDs were calibrated in Co-60 and reported on absorbed dose in water per target dose (μGy/Gy) as well as thermal neutron dose equivalent per target dose (μSv/Gy). Additionally, bubble detectors for personal neutron dosimetry (BD-PND) were used for measuring neutrons (>50 keV), which were calibrated in a Cf-252 neutron beam to report on neutron dose equivalent dose data. The Monte Carlo code TOPAS (version 3.6) was run using a phase-space file containing 1010 histories reaching an average standard statistical uncertainty of less than 0.2% (coverage factor k = 1) on all voxels scoring more than 50% of the maximum dose. The primary beam was modeled following a Fermi–Eyges description of the spot envelope fitted to measurements. For the Monte Carlo simulation, the chemical composition of the tissues represented in ATOM was employed. The dose was tallied as dose-to-water, and data were normalized to the target dose (physical dose) to report on absorbed doses per target dose (mSv/Gy) or neutron dose equivalent per target dose (μSv/Gy), while also an estimate of the total organ dose was provided for a target dose of 50.4 Gy(RBE). Out-of-field doses showed absorbed doses that were 5 to 6 orders of magnitude lower than the target dose. The discrepancy between TLD data and the corresponding scored values in the Monte Carlo calculations involving proton and gamma contributions was on average 18%. The comparison between the neutron equivalent doses between the Monte Carlo simulation and the measured neutron doses was on average 8%. Organ dose calculations revealed the highest dose for the thyroid, which was 120 mSv, while other organ doses ranged from 18 mSv in the lungs to 0.6 mSv in the testes. The proposed computational method for routine calculation of the out-of-the-field dose in proton therapy produces results that are compatible with the experimental data and allow to calculate out-of-field organ doses during proton therapy.

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Section: Discussionmentioning

confidence: 83%

Section: Methodsmentioning

confidence: 99%

Validation of a Monte Carlo Framework for Out-of-Field Dose Calculations in Proton Therapy

et al. 2022

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“…Regarding the experimental uncertainties, the maximum statistical uncertainty of the scored charge with the extrapolation IC yielded

0.9 %

. The other experimental uncertainties concerned the determination of the WED: Facility‐dependent uncertainties resulting in energy fluctuations of 0.05 MeV 29 corresponded to 0.08 mm range in water for 120 MeV protons (NIST) 32 . There was also an uncertainty in the physical thickness of the absorber materials used, which affected the resulting WED.…”

Section: Methodsmentioning

confidence: 99%

“…The same material composition of the aluminum alloy was used as for the measurements, with a density of 2.66 g/

c {normalm}^{3}

29 . The composition of RW3 as specified above resulted in a density of 1.045 g/

c {normalm}^{3}

.…”

Section: Methodsmentioning

confidence: 99%

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Technical note: Providing proton fields down to the few‐MeV level at clinical pencil beam scanning facilities for radiobiological experiments

et al. 2021

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The adequate performance of radiobiological experiments using clinical proton beams typically requires substantial preparations to provide the appropriate setup for specific experiments. Providing radiobiologically interesting low-energy protons is a particular challenge, due to various physical effects that become more pronounced with larger absorber thickness and smaller proton energy. This work demonstrates the generation of decelerated low-energy protons from a clinical proton beam. Methods: Monte Carlo simulations of proton energy spectra were performed for energy absorbers with varying thicknesses to reduce the energy of the clinical proton beam down to the few-MeV level corresponding to μm-ranges. In this way, a setup with an optimum thickness of the absorber with a maximum efficiency of the proton fluence for the provisioning of low-energy protons is supposed to be found. For the specific applications of 2.5-3.3 MeV protons and 𝛼-particle range equivalent protons, the relative depth dose was measured and simulated together with the dose-averaged linear energy transfer (LETd) distribution. Results:The resulting energy spectra from Monte Carlo simulations indicate an optimal absorber thickness for providing low-energy protons with maximum efficiency of proton fluence at an user-requested energy range for experiments. For instance, providing energies lower than 5 MeV, an energy spectrum with a relative total efficiency of 38.6% to the initial spectrum was obtained with the optimal setup. The measurements of the depth dose, compared to the Monte Carlo simulations, showed that the dosimetry of low-energy protons works and protons with high LETd down to the range of 𝛼-particles can be produced. Conclusions: This work provides a method for generating all clinically and radiobiologically relevant energies -especially down to the few-MeV levelat one clinical facility with pencil beam scanning. Thereby, it enables radiobiological experiments under environmentally uniform conditions.

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Treatment planning of scanned proton beams in RayStation

Janson,

Glimelius,

Fredriksson

et al. 2024

Medical Dosimetry

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Experiments and Monte Carlo simulations on multiple Coulomb scattering of protons

Cited by 6 publications

References 39 publications

Validation of a Monte Carlo Framework for Out-of-Field Dose Calculations in Proton Therapy

Validation of a Monte Carlo Framework for Out-of-Field Dose Calculations in Proton Therapy

Technical note: Providing proton fields down to the few‐MeV level at clinical pencil beam scanning facilities for radiobiological experiments

Treatment planning of scanned proton beams in RayStation

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