Output factor comparison of Monte Carlo and measurement for Varian TrueBeam 6 MV and 10 MV flattening filter‐free stereotactic radiosurgery system

Cheng, J.; Ning, Holly; Arora, Barbara; Zhuge, Ying; Miller, Robert W.

doi:10.1120/jacmp.v17i3.5956

Cited by 24 publications

(33 citation statements)

References 26 publications

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“…One of the most critical parameters is the output factor (OF), which is especially sensitive to the detector used and to the field size 6,7 . Many publications reported experimental dosimetric data of conical collimators for stereotactic radiosurgery 8–18 . However, in most of those publications, the reported dosimetric data were acquired in a diversity of setups, which makes difficult to establish comparisons.…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo simulation of conical collimators for stereotactic radiosurgery with a 6 MV flattening‐filter‐free photon beam

Hermida-López

Sánchez-Artuñedo

Rodríguez³

et al. 2021

Medical Physics

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Purpose: Conical collimators, or cones, are tertiary collimators that attach to a radiotherapy linac and are suited for the stereotactic radiosurgery treatment of small brain lesions. The small diameter of the most used cones makes difficult the acquisition of the dosimetry data needed for the commissioning of treatment planning systems. Although many publications report dosimetric data of conical collimators for stereotactic radiosurgery, most of the works use different setups, which complicates comparisons. In other cases, the cone output factors reported do not take into account the effect of the small cone diameter on the detector response. Finally, few data exist on the dosimetry of cones with flattening-filter-free (FFF) beams from modern linac models. This work aims at obtaining a dosimetric characterization of the conical collimators manufactured by Brainlab AG (Munich, Germany) in a 6 MV FFF beam from a TrueBeam STx linac (Varian Medical Systems). Methods: Percentage depth dose curves, lateral dose profiles and cone output factors were obtained using Monte Carlo simulations for the cones with diameters of 4,

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Section: Introductionmentioning

confidence: 99%

Monte Carlo simulation of conical collimators for stereotactic radiosurgery with a 6 MV flattening‐filter‐free photon beam

Hermida-López

Sánchez-Artuñedo

Rodríguez³

et al. 2021

Medical Physics

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“…There are number of publications on MC modeling of small fields for the Varian TrueBeam linac . A limited number of publications exist on dosimetry of stereotactic cones manufactured by Varian, BrainLab and Elekta .…”

Section: Introductionmentioning

confidence: 99%

Dosimetric characterization of Elekta stereotactic cones

Borzov

Nevelsky

Bar-Deroma

et al. 2017

J Applied Clin Med Phys

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PurposeDosimetry of small fields defined by stereotactic cones remains a challenging task. In this work, we report the results of commissioning measurements for the new Elekta stereotactic conical collimator system attached to the Elekta VersaHD linac and present the comparison between the measured and Monte Carlo (MC) calculated data for the 6 MV FFF beam. In addition, relative output factor (ROF) dependence on the stereotactic cone aperture variation was studied and penumbra comparison for small MLC‐based and cone‐based fields was performed.MethodsCones with nominal diameters of 15 mm, 12.5 mm, 10 mm, 7.5 mm, and 5 mm were employed in our study. Percentage depth dose (PDD), off‐axis ratios (OAR), and ROF were measured using a stereotactic field diode (SFD). BEAMnrc code was used for MC simulations.ResultsMC calculated and measured PDDs for all cones agreed within 1%/0.5 mm, and OAR profiles agreed within 1%/0.5 mm. ROF obtained from the measurements and MC calculations agreed within 2% for all cone sizes. Small‐field correction factors for the SFD detector Kfield,3 × 3(SFD) were derived using MC calculations as a baseline and were found to be 0.982, 0.992, 0.997, 1.015, and 1.017 for the 5, 7.5, 10, 12.5, and 15‐mm cones respectively. The difference in ROF was about 10%, 6%, 3.5%, 3%, 2.5%, and 2% for ±0.3 mm variations in 5, 7.5, 10, 12.5, and 15‐mm cone aperture respectively. In case of single static field, cone‐based collimation produced a sharper penumbra compared to the MLC‐based.ConclusionsAccurate MC simulation can be an effective tool for verification of dosimetric measurements of small fields. Due to the very high sensitivity of output factors on the cone diameter, manufacture‐related variations in cone size may lead to considerable variations in dosimetric characteristics of stereotactic cones.

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“…A reliable, secondary verification should be performed with difficult or complex treatment plans or in stereotactic radiosurgery (SRS) cases requiring high doses in one fraction. 27,38 Although there are limitations in the dose calculation algorithms used in commercial planning systems, programs for calculating dose using Monte Carlo are often deemed sufficient. However, although Monte Carlo-based dose calculation has distinct advantages, it can cause differences in results based on the accuracy of position or the material composition 21 and also it requires more time to calculation.…”

Section: Discussionmentioning

confidence: 99%

“…Resolution of a voxel was 0.4 × 0.4 × 0.4 cm 3 and the physics range cut was set to 0.1 mm. 21,[26][27][28] For all the calculations, a source-to-surface distance (SSD) of 100 cm was used. The dose calculation results were generated as 3D structures to be analyzed using the program.…”

Section: B | Linac Modelingmentioning

confidence: 99%

Feasibility of a GATE Monte Carlo platform in a clinical pretreatment QA system for VMAT treatment plans using TrueBeam with an HD120 multileaf collimator

Lee

Jeong

Chung

et al. 2019

J Applied Clin Med Phys

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PurposeTo evaluate the quality of patient‐specific complicated treatment plans, including commercialized treatment planning systems (TPS) and commissioned beam data, we developed a process of quality assurance (QA) using a Monte Carlo (MC) platform. Specifically, we constructed an interface system that automatically converts treatment plan and dose matrix data in digital imaging and communications in medicine to an MC dose‐calculation engine. The clinical feasibility of the system was evaluated.Materials and MethodsA dose‐calculation engine based on GATE v8.1 was embedded in our QA system and in a parallel computing system to significantly reduce the computation time. The QA system automatically converts parameters in volumetric‐modulated arc therapy (VMAT) plans to files for dose calculation using GATE. The system then calculates dose maps. Energies of 6 MV, 10 MV, 6 MV flattening filter free (FFF), and 10 MV FFF from a TrueBeam with HD120 were modeled and commissioned. To evaluate the beam models, percentage depth dose (PDD) values, MC calculation profiles, and measured beam data were compared at various depths (Dmax, 5 cm, 10 cm, and 20 cm), field sizes, and energies. To evaluate the feasibility of the QA system for clinical use, doses measured for clinical VMAT plans using films were compared to dose maps calculated using our MC‐based QA system.ResultsA LINAC QA system was analyzed by PDD and profile according to the secondary collimator and multileaf collimator (MLC). Values for MC calculations and TPS beam data obtained using CC13 ion chamber (IBA Dosimetry, Germany) were consistent within 1.0%. Clinical validation using a gamma index was performed for VMAT treatment plans using a solid water phantom and arbitrary patient data. The gamma evaluation results (with criteria of 3%/3 mm) were 98.1%, 99.1%, 99.2%, and 97.1% for energies of 6 MV, 10 MV, 6 MV FFF, and 10 MV FFF, respectively.ConclusionsWe constructed an MC‐based QA system for evaluating patient treatment plans and evaluated its feasibility in clinical practice. We observed robust agreement between dose calculations from our QA system and measurements for VMAT plans. Our QA system could be useful in other clinical settings, such as small‐field SRS procedures or analyses of secondary cancer risk, for which dose calculations using TPS are difficult to verify.

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Output factor comparison of Monte Carlo and measurement for Varian TrueBeam 6 MV and 10 MV flattening filter‐free stereotactic radiosurgery system

Cited by 24 publications

References 26 publications

Monte Carlo simulation of conical collimators for stereotactic radiosurgery with a 6 MV flattening‐filter‐free photon beam

Monte Carlo simulation of conical collimators for stereotactic radiosurgery with a 6 MV flattening‐filter‐free photon beam

Dosimetric characterization of Elekta stereotactic cones

Feasibility of a GATE Monte Carlo platform in a clinical pretreatment QA system for VMAT treatment plans using TrueBeam with an HD120 multileaf collimator

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