A novel verification method using a plastic scintillator imagining system for assessment of gantry sag in radiotherapy

Tsuneda, Masato; Nishio, Teiji; Saito, A.; Tanaka, Sodai; Suzuki, Tatsuro; Kawahara, Daisuke; Matsushita, K.; Nishio, Aya; Ozawa, Shogo; Karasawa, Kumiko; Nagata, Yasushi

doi:10.1002/mp.12922

Cited by 8 publications

(8 citation statements)

References 19 publications

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“…We developed Winston-Lutz-Gao test two years ago for single iso-multiple mets treatment with use of an old Varian 21EX machine. Since then, several relevant articles [5] [6] [7] were published that started to verify either the dosimetric or geometric accuracy of the single iso-multiple mets treatment technique. We will discuss these articles later in this article.…”

Section: Introductionmentioning

confidence: 99%

Winston-Lutz-Gao Test on the True Beam STx Linear Accelerator

Gao¹,

Liu²

2019

IJMPCERO

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In the linear accelerator-based stereotactic radio surgery (SRS) and stereotactic body radiotherapy (SBRT) programs, single isocenter-multiple metastases' treatment has become more and more popular due to their high efficiency in treatment time. However, the absence of a comprehensive quality assurance program is still the challenge for medical physicists. The Winston-Lutz-Gao test, which we developed two years ago, was performed for the first time on a True Beam STx (Varian Medical System) linear accelerator in this study. Beams were designed by Eclipse with gantry, collimator, and couch full rotations, and a 200-pound weight was placed on the couch to mimic real treatment. The "frameless SRS QA target pointer" from the Brainlab company, with a 3.5-mm metallic ball embedded in the center, was used as a phantom. Images were acquired by the portal imager built-in linear accelerator and analyzed directly by the Image browser in ARIA. We found that the farther the metastases were from the linac isocenter, the worse the congruence was between the beam mechanical and the radiation center. The farthest metastases should be within 6 cm from the linac isocenter per the AAPM TG-142 and American Society for Radiation Oncology (ASTRO) white paper criteria. To the best of our knowledge, this is the first off-isocenter Winston-Lutz test performed on a True Beam STx linear accelerator.

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Section: Introductionmentioning

confidence: 99%

Winston-Lutz-Gao Test on the True Beam STx Linear Accelerator

Gao¹,

Liu²

2019

IJMPCERO

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“…The development of a measurement system for the 3D beam alignment has been reported 18 . We improved this system with a scintillating screen.…”

Section: Methodsmentioning

confidence: 99%

Plastic scintillation dosimeter with a conical mirror for measuring 3D dose distribution

et al. 2021

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To test the measurement technique of the three-dimensional (3D) dose distribution measured image by capturing the scintillation light generated using a plastic scintillator and a scintillating screen. Methods: Our imaging system constituted a column shaped plastic scintillator covered by a Gd 2 O 2 S:Tb scintillating screen, a conical mirror and a cooled CCD camera. The scintillator was irradiated with 6 MV photon beams. Meanwhile, the irradiated plan was prepared for the static field plans, two-field plan (2F plan) and the conformal arc plan (CA plan). The 2F plan contained 16 mm 2 and 10 mm 2 fields irradiated from gantry angles of 0 • and 25 • , respectively. The gantry was rotated counterclockwise from 45 • to 315 • for the CA plan. The field size was then obtained as 10 mm 2 . A Monte Carlo simulation was performed in the experimental geometry to obtain the calculated 3D dose distribution as the reference data. Dose response was acquired by comparing between the reference and the measurement. The dose rate dependence was verified by irradiating the same MU value at different dose rates ranging from 100 to 600 MU/min. Deconvolution processing was applied to the measured images for the correction of light blurring. The measured 3D dose distribution was reconstructed from each measured image. Gamma analysis was performed to these 3D dose distributions. The gamma criteria were 3% for the dose difference, 2 mm for the distance-to-agreement and 10% for the threshold. Results: Dose response for the scintillation light was linear. The variation in the light intensity for the dose rate ranging from 100 to 600 MU/min was less than 0.5%, while our system presents dose rate independence. For the 3D dose measurement, blurring of light through deconvolution processing worked well. The 3D gamma passing rate (3D GPR) for the 10 × 10 mm 2 , 16 × 16 mm 2 , and 20 × 20 mm 2 fields were observed to be 99.3%, 98.8%, and 97.8%, respectively. Reproducibility of measurement was verified. The 3D GPR results for the 2F plan and the CA plan were 99.7% and 100%, respectively. Conclusions: We developed a plastic scintillation dosimeter and demonstrated that our system concept can act as a suitable technique for measuring the 3D dose distribution from the gamma results. In the future, we will attempt to measure the 4D dose distribution for clinical volumetric modulated arc radiation therapy (VMAT)-SBRTplans.

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“…Tsuneda et al. studied 3D QA tool based on the scintillator imaging system for verification of 3D isocentricity and direct evaluation of the sagging angle using plastic scintillator and CCD camera 12 …”

Section: Introductionmentioning

confidence: 99%

3D star shot analysis using MAGAT gel dosimeter for integrated imaging and radiation isocenter verification of MR‐Linac system

Kim

Shin

et al. 2022

J Applied Clin Med Phys

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This study aims to investigate a star shot analysis using a threedimensional (3D) gel dosimeter for the imaging and radiation isocenter verification of a magnetic resonance linear accelerator (MR-Linac). Methods: A mixture of methacrylic acid, gelatin, and tetrakis (hydroxymethyl) phosphonium chloride, called MAGAT gel, was fabricated. One MAGAT gel for each Linac and MR-Linac was irradiated under six gantry angles. A 6 MV photon beam of Linac and a 6 MV flattening filter free beam of MR-Linac were delivered to two MAGAT gels and EBT3 films. MR images were acquired by MR-Linac with a clinical sequence (i.e., TrueFISP). The 3D star shot analysis for seven consecutive slices of the MR images with TrueFISP was performed. The 2D star shot analysis for the central plane of the gel was compared to the results from the EBT3 films. The radius of isocircle (IC r ) and the distance between the center of the circle and the center marked on the image (IC d ) were evaluated. Results: For MR-Linac with MAGAT gel measurements, IC d at the central plane was 0.46 mm for TrueFISP. Compared to EBT3 film measurements, the differences in IC d and IC r for both Linac and MR-Linac were within 0.11 and 0.13 mm, respectively. For the 3D analysis, seven consecutive slices of TrueFISP images were analyzed and the maximum radii of isocircles (IC r_max ) were 0.18 mm for Linac and 0.73 mm for MR-Linac. The tilting angles of radiation axis were 0.31 • for Linac and 0.10 • for MR-Linac. Conclusion:The accuracy of 3D star shot analysis using MAGAT gel was comparable to that of EBT3 film, having a capability for integrated analysis for imaging isocenter and radiation isocenter.3D star shot analysis using MAGAT gel can provide 3D information of radiation isocenter, suggesting a quantitative extent of gantry-tilting.

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A novel verification method using a plastic scintillator imagining system for assessment of gantry sag in radiotherapy

Cited by 8 publications

References 19 publications

Winston-Lutz-Gao Test on the True Beam STx Linear Accelerator

Winston-Lutz-Gao Test on the True Beam STx Linear Accelerator

Plastic scintillation dosimeter with a conical mirror for measuring 3D dose distribution

3D star shot analysis using MAGAT gel dosimeter for integrated imaging and radiation isocenter verification of MR‐Linac system

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