Monte Carlo investigation of the low-dose envelope from scanned proton pencil beams

Sawakuchi, Gabriel O.; Titt, Uwe; Mirković, Dragan; Ciangaru, G.; Zhu, Xiaorong Ronald; Sahoo, Narayan; Gillin, Michael; Mohan, Radhe

doi:10.1088/0031-9155/55/3/011

Cited by 55 publications

(78 citation statements)

References 18 publications

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“…Rather than a detailed single‐spot profile validation of the halo,7, 12, 30, 31, 32 field size factors (FSF) for square fields with 4 mm spacing and 1 MU per spot of monoenergetic proton beams, described by Pedroni et al,4 Sawakuchi et al,33 Zhu et al,34 and Shen et al,35 were used to investigate the accuracy of the halo both with and without the range shifter. A water phantom (Digiphant,IBA Dosimetry, Schwarzenbruck, Germany), which combines a two‐dimensional ionization chamber array (MatriXX PT ® , IBA Dosimetry, Schwarzenbruck, Germany) dedicated to address the high‐dose rates in PBS, in a waterproof housing that can be scanned in a water phantom, was used to measure the two‐dimensional (2D) dose distributions in selected depth perpendicular to the beam incident direction 36.…”

Section: Methodsmentioning

confidence: 99%

Validation and clinical implementation of an accurate Monte Carlo code for pencil beam scanning proton therapy

Huang

Kang

Souris

et al. 2018

J Applied Clin Med Phys

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Monte Carlo (MC)‐based dose calculations are generally superior to analytical dose calculations (ADC) in modeling the dose distribution for proton pencil beam scanning (PBS) treatments. The purpose of this paper is to present a methodology for commissioning and validating an accurate MC code for PBS utilizing a parameterized source model, including an implementation of a range shifter, that can independently check the ADC in commercial treatment planning system (TPS) and fast Monte Carlo dose calculation in opensource platform (MCsquare). The source model parameters (including beam size, angular divergence and energy spread) and protons per MU were extracted and tuned at the nozzle exit by comparing Tool for Particle Simulation (TOPAS) simulations with a series of commissioning measurements using scintillation screen/CCD camera detector and ionization chambers. The range shifter was simulated as an independent object with geometric and material information. The MC calculation platform was validated through comprehensive measurements of single spots, field size factors (FSF) and three‐dimensional dose distributions of spread‐out Bragg peaks (SOBPs), both without and with the range shifter. Differences in field size factors and absolute output at various depths of SOBPs between measurement and simulation were within 2.2%, with and without a range shifter, indicating an accurate source model. TOPAS was also validated against anthropomorphic lung phantom measurements. Comparison of dose distributions and DVHs for representative liver and lung cases between independent MC and analytical dose calculations from a commercial TPS further highlights the limitations of the ADC in situations of highly heterogeneous geometries. The fast MC platform has been implemented within our clinical practice to provide additional independent dose validation/QA of the commercial ADC for patient plans. Using the independent MC, we can more efficiently commission ADC by reducing the amount of measured data required for low dose “halo” modeling, especially when a range shifter is employed.

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Section: Methodsmentioning

confidence: 99%

Validation and clinical implementation of an accurate Monte Carlo code for pencil beam scanning proton therapy

Huang

Kang

Souris

et al. 2018

J Applied Clin Med Phys

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“…Secondary particles are generated through nonelastic nuclear interactions and include secondary protons and other fragments (deuterons, tritons, alphas, neutrons, etc.). 14 The beamlet dose distribution is assumed to have radial symmetry and can be written as 10,18,19 …”

Section: Iib1 Pencil Beam Algorithmmentioning

confidence: 99%

“…Recently, we have demonstrated that the SG fluence model is not accurate enough because of the contributions of large angle scattering from the devices within the Hitachi scanning nozzle. 14,15 In general, σ i in the x and y directions are different due to the elliptical shape of the initial beam. For the first Gaussian, the values of σ 1 in the x and y directions change with the gantry angle due to changes in the magnetic fields of steering and focusing magnets with the treatment gantry rotation.…”

Section: Iib2 Single and Double Gaussian Fluence Modelsmentioning

confidence: 99%

“…4,11 However, our recent works have demonstrated that a SG function could not describe in-air lateral profiles well for an individual pencil beam from our scanning nozzle. [12][13][14][15] The TPS vendor, therefore, implemented a double Gaussian (DG) fluence model to account for the spot fluence due to contributions of large angle scattering from the devices within the scanning nozzle. In this work, we present our method and experience of commissioning a pencil beam algorithm with DG fluence model.…”

Section: Introductionmentioning

confidence: 99%

“…4,14,15 It should be noted that the parameters in Eq. (2) are not adjustable for the purpose of commissioning the TPS.…”

mentioning

confidence: 99%

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Commissioning dose computation models for spot scanning proton beams in water for a commercially available treatment planning system

et al. 2013

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Purpose: To present our method and experience in commissioning dose models in water for spot scanning proton therapy in a commercial treatment planning system (TPS). Methods: The input data required by the TPS included in-air transverse profiles and integral depth doses (IDDs). All input data were obtained from Monte Carlo (MC) simulations that had been validated by measurements. MC-generated IDDs were converted to units of Gy mm 2 /MU using the measured IDDs at a depth of 2 cm employing the largest commercially available parallel-plate ionization chamber. The sensitive area of the chamber was insufficient to fully encompass the entire lateral dose deposited at depth by a pencil beam (spot). To correct for the detector size, correction factors as a function of proton energy were defined and determined using MC. The fluence of individual spots was initially modeled as a single Gaussian (SG) function and later as a double Gaussian (DG) function. The DG fluence model was introduced to account for the spot fluence due to contributions of large angle scattering from the devices within the scanning nozzle, especially from the spot profile monitor. To validate the DG fluence model, we compared calculations and measurements, including doses at the center of spread out Bragg peaks (SOBPs) as a function of nominal field size, range, and SOBP width, lateral dose profiles, and depth doses for different widths of SOBP. Dose models were validated extensively with patient treatment field-specific measurements. Results: We demonstrated that the DG fluence model is necessary for predicting the field size dependence of dose distributions. With this model, the calculated doses at the center of SOBPs as a function of nominal field size, range, and SOBP width, lateral dose profiles and depth doses for rectangular target volumes agreed well with respective measured values. With the DG fluence model for our scanning proton beam line, we successfully treated more than 500 patients from March 2010 through June 2012 with acceptable agreement between TPS calculated and measured dose distributions. However, the current dose model still has limitations in predicting field size dependence of doses at some intermediate depths of proton beams with high energies. Conclusions: We have commissioned a DG fluence model for clinical use. It is demonstrated that the DG fluence model is significantly more accurate than the SG fluence model. However, some deficiencies in modeling the low-dose envelope in the current dose algorithm still exist. Further improvements to the current dose algorithm are needed. The method presented here should be useful for commissioning pencil beam dose algorithms in new versions of TPS in the future.

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Comparison of multi‐institutional Varian ProBeam pencil beam scanning proton beam commissioning data

Langner

Eley

Dong

et al. 2017

J Applied Clin Med Phys

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PurposeCommissioning beam data for proton spot scanning beams are compared for the first two Varian ProBeam sites in the United States, at the Maryland Proton Treatment Center (MPTC) and Scripps Proton Therapy Center (SPTC). In addition, the extent to which beams can be matched between gantry rooms at MPTC is investigated.MethodBeam data for the two sites were acquired with independent dosimetry systems and compared. Integrated depth dose curves (IDDs) were acquired with Bragg peak ion chambers in a 3D water tank for pencil beams at both sites. Spot profiles were acquired at different distances from the isocenter at a gantry angle of 0° as well as a function of gantry angles. Absolute dose calibration was compared between SPTC and the gantries at MPTC. Dosimetric verification of test plans, output as a function of gantry angle, monitor unit (MU) linearity, end effects, dose rate dependence, and plan reproducibility were compared for different gantries at MPTC.ResultsThe IDDs for the two sites were similar, except in the plateau region, where the SPTC data were on average 4.5% higher for lower energies. This increase in the plateau region decreased as energy increased, with no marked difference for energies higher than 180 MeV. Range in water coincided for all energies within 0.5 mm. The sigmas of the spot profiles in air were within 10% agreement at isocenter. This difference increased as detector distance from the isocenter increased. Absolute doses for the gantries measured at both sites were within 1% agreement. Test plans, output as function of gantry angle, MU linearity, end effects, dose rate dependence, and plan reproducibility were all within tolerances given by TG142.ConclusionBeam data for the two sites and between different gantry rooms were well matched.

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Monte Carlo investigation of the low-dose envelope from scanned proton pencil beams

Cited by 55 publications

References 18 publications

Validation and clinical implementation of an accurate Monte Carlo code for pencil beam scanning proton therapy

Validation and clinical implementation of an accurate Monte Carlo code for pencil beam scanning proton therapy

Commissioning dose computation models for spot scanning proton beams in water for a commercially available treatment planning system

Comparison of multi‐institutional Varian ProBeam pencil beam scanning proton beam commissioning data

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