Real‐time simulator for designing electron dual scattering foil systems

Carver, Robert L.; Hogstrom, Kenneth R.; Price, Michael; LeBlanc, Justin D.; Pitcher, Garrett M.

doi:10.1120/jacmp.v15i6.4849

Cited by 4 publications

(6 citation statements)

References 8 publications

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“…The primary scattering foils broaden the beam, and the secondary foils, flatten the beam. (21,22) The tungsten cross-plane (upper) and in-plane (lower) X-ray collimators, or jaws, collimate the beam as it exits the treatment head. Both the multileaf collimator (MLC) and upper jaws are designed with curved inner edges, whereas the lower jaws are positioned to align with the divergence of the beam.…”

Section: A Configuration Of Acceleratormentioning

confidence: 99%

“…We have been investigating new electron scattering foil and collimation system designs for 6-20 MeV beams on the Elekta radiotherapy accelerator. Using a real-time, dual scattering foil simulator, (21) LeBlanc (22) studied multiple dual scattering foil designs with results indicating that uniformity of 7-20 MeV beams using two secondary foils might be possible, demonstrating one secondary foil for 7-13 MeV and one for 16-20 MeV beams.…”

Section: Introductionmentioning

confidence: 99%

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Radiation leakage dose from Elekta electron collimation system

Pitcher

Hogstrom

Carver

2016

J Applied Clin Med Phys

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This study provided baseline data required for a greater project, whose objective was to design a new Elekta electron collimation system having significantly lighter electron applicators with equally low out‐of field leakage dose. Specifically, off‐axis dose profiles for the electron collimation system of our uniquely configured Elekta Infinity accelerator with the MLCi2 treatment head were measured and calculated for two primary purposes: 1) to evaluate and document the out‐of‐field leakage dose in the patient plane and 2) to validate the dose distributions calculated using a BEAMnrc Monte Carlo (MC) model for out‐of‐field dose profiles. Off‐axis dose profiles were measured in a water phantom at 100 cm SSD for 1 and 2 cm depths along the in‐plane, cross‐plane, and both diagonal axes using a cylindrical ionization chamber with the 10×10 and 20×20 cm2 applicators and 7, 13, and 20 MeV beams. Dose distributions were calculated using a previously developed BEAMnrc MC model of the Elekta Infinity accelerator for the same beam energies and applicator sizes and compared with measurements. Measured results showed that the in‐field beam flatness met our acceptance criteria (±3% on major and ±4% on diagonal axes) and that out‐of‐field mean and maximum percent leakage doses in the patient plane met acceptance criteria as specified by the International Electrotechnical Commission (IEC). Cross‐plane out‐of‐field dose profiles showed greater leakage dose than in‐plane profiles, attributed to the curved edges of the upper X‐ray jaws and multileaf collimator. Mean leakage doses increased with beam energy, being 0.93% and 0.85% of maximum central axis dose for the 10×10 and 20×20 cm2 applicators, respectively, at 20 MeV. MC calculations predicted the measured dose to within 0.1% in most profiles outside the radiation field; however, excluding modeling of nontrimmer applicator components led to calculations exceeding measured data by as much as 0.2% for some regions along the in‐plane axis. Using EGSnrc LATCH bit filtering to separately calculate out‐of‐field leakage dose components (photon dose, primary electron dose, and electron dose arising from interactions in various collimating components), MC calculations revealed that the primary electron dose in the out‐of‐field leakage region was small and decreased as beam energy increased. Also, both the photon dose component and electron dose component resulting from collimator scatter dominated the leakage dose, increasing with increasing beam energy. We concluded that our custom Elekta Infinity with the MLCi2 treatment head met IEC leakage dose criteria in the patient plane. Also, accuracy of our MC model should be sufficient for our use in the design of a new, improved electron collimation system.PACS number(s): 87.56.nk, 87.10.Rt, 87.56.J

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Section: A Configuration Of Acceleratormentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Radiation leakage dose from Elekta electron collimation system

Pitcher

Hogstrom

Carver

2016

J Applied Clin Med Phys

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“…Variation of the width of the radial dose distribution

{r_{1/e}}

according to depth for electron pencil beam incident upon water. Calculations obtained according to the Fermi and Eyges theory with the reduced Gaussian distribution (RG), 27 Kainz et al., 24 ICRU 19 are shown for the 10 MeV beam (without range straggling correction). The variation of the width of the radial dose distribution

{r_{1/e}}

with depth obtained using the model by Kainz et al., 24 the modified calculation including the range straggling model (Equation ) and MC simulations are shown for the 100–150–200 MeV electron beams.…”

Section: Resultsmentioning

confidence: 99%

“…In some studies, where large deviations are treated separately, the Gaussian part of the Molière scattering power was found to overestimate the width of the angular distribution 21 . A reduced Gaussian distribution was therefore defined using θ RG 27 (Eq. S11, Supplementary data).…”

Section: Methodsmentioning

confidence: 99%

Very high‐energy electron dose calculation using the Fermi‐Eyges theory of multiple scattering and a simplified pencil beam model

Ronga,

Deut,

Bonfrate

et al. 2023

Medical Physics

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BackgroundVery high‐energy electrons (VHEE) radiotherapy, in the energy range of 100–200 MeV is currently considered a promising technique for the future of radiation therapy and could benefit from the promises of ultra‐high dose rate FLASH therapy. However, to our knowledge, no analytical calculation models have been tested for this type of application and the approximations proposed for multiple scattering with electron beams have not been extensively evaluated at these high energies.PurposeIn this work, we discuss the derivation of a simple and fast algorithm based on the Fermi‐Eyges theory of multiple Coulomb scattering for fast dose calculation for VHEE beams (up to 200 MeV). Similar to the Gaussian pencil beam models used for electron or proton beams, this pencil beam kernel is separated into a central and an off‐axis term. Monte Carlo simulations are performed to compare the analytical calculations with simulations and to determine the parametrizations used in the model at the highest electron energies.MethodsThe normalized electron planar fluence distribution is described in water according to the Fermi‐Eyges theory of multiple Coulomb scattering and a double Gaussian distribution model. The main quantities used in the model and their calculation (mass angular scattering power, mean energy, range straggling) are discussed and tested for electron energies up to 200 MeV. The TOPAS/Geant4 Monte Carlo (MC) toolkit is used to compare analytical calculations with MC simulations for a theoretical pencil beam irradiation and to find the best parameters describing the range straggling. The model is then tested on a realistic simulation of a pencil beam scanning beamline with treatment field dimensions up to 15 × 15 cm2 and for deep‐seated targets.ResultsRadial dose distributions of a pencil beam in water were calculated with the model and compared with the results of a complete Monte Carlo simulation. A good agreement (within 2%/2 mm gamma passing rate superior to 90%, and a mean deviation between calculated and simulated pencil beam radial spread smaller than 0.6 mm) was observed between analytical dose distributions and simulations for energies up to 200 MeV and field sizes up to 15 × 15 cm2.ConclusionsA parameterization of an electron source and an analytical pencil beam model were proposed in this work, thereby allowing a suitable reproduction of the lateral fluence of a VHEE beam and good agreement between calculations and simulated data. Further improvement of the method would require the consideration of a model describing the large‐angle scattering of the electrons. The results of this work could support future research into VHEE radiotherapy and might be of interest for use together with VHEE broad beams produced by scanned narrow pencil beams.

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“…The radiation field from the research accelerator is not flat, as is typical for a clinical linear accelerator, and without any electron dual scattering foil systems [46,47] for electron beam flattening (as used in the second experiment with the calorimeter) the radiation field shows a Gaussian shape (Figure 4). There is good agreement between the relative lateral ionization measurement with the Advanced Markus ionization chamber and the alanine measurements at different DPP.…”

Section: Dose Per Beam Pulse Charge From Alanine Measurementsmentioning

confidence: 99%

Calorimeter for Real-Time Dosimetry of Pulsed Ultra-High Dose Rate Electron Beams

et al. 2020

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An aluminum calorimeter was investigated as a possible real-time dosimeter for electron beams with an ultra-high dose per pulse (DPP), as used in FLASH radiation therapy (a few Gy/pulse). Ionization chambers, the most widely used active dosimeter type in conventional external beam radiation therapy, suffer from large ion recombination losses at these conditions. Passive dosimeters, such as alanine, are independent of dose rate but do not provide real-time read-out. In this work it is shown that the response of alanine is independent of the DPP in the investigated ultra-high DPP range (up to 2.3 Gy/pulse). Alanine dose measurements were then used to determine the ion recombination correction for an Advanced Markus plane-parallel ionization chamber at ultra-high DPP. Ion collection losses larger than 50% were observed. Therefore, ionization chambers are not considered suitable for accurate dosimetry in FLASH radiation therapy. As an alternative, in a second (independent) experiment an aluminum open-to-atmosphere calorimeter, operated in the quasi-adiabatic mode was investigated at ultra-high DPP electron radiation. The beam pulse charge, and thus the DPP, was varied to evaluate the linearity of the calorimeter response in the DPP range between 0.3 and 1.8 Gy/pulse. On average, the standard deviation of the calorimeter response was 0.1%. The response was proportional to the DPP in the investigated range. The average deviation of the linear fit of the calorimeter dose as a function of the beam pulse charge was <0.5%. This preliminary investigation suggests that a simplified calorimeter design is suitable as a dosimeter with real-time read-out for clinical FLASH radiation therapy beams.

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Real‐time simulator for designing electron dual scattering foil systems

Cited by 4 publications

References 8 publications

Radiation leakage dose from Elekta electron collimation system

Radiation leakage dose from Elekta electron collimation system

Very high‐energy electron dose calculation using the Fermi‐Eyges theory of multiple scattering and a simplified pencil beam model

Calorimeter for Real-Time Dosimetry of Pulsed Ultra-High Dose Rate Electron Beams

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