A method for accurate zero calibration of asymmetric jaws in single-isocenter half-beam techniques

Hernández, Víctor; Sempau, J.; Abella, Raúl; López, M. A.; Pérez, Manuel Asensi; Artigues, Manel; Arenas, Meritxell

doi:10.1118/1.4773314

Cited by 5 publications

(5 citation statements)

References 24 publications

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“…The largest difference in field size among the linacs is 0.4 mm and the largest junction jaw offset is 0.2 mm (Table 4). Hernandez et al 23 reported field junction‐dosages between −4.5% and 5.2% which is higher than our results where the field junction dosages are between −2.5 and 1.2%. However, this is presumably due to difference in linac models of the studies.…”

Section: Discussioncontrasting

confidence: 98%

“…This method has uncertainties regarding visual estimation and radiation‐ and light field agreement 6 . For TrueBeam linacs, several publications have suggested using the Electronic Portal Imaging Device (EPID) to evaluate and calibrate the jaw position 22,23 . It has been shown that using EPID results in higher precision and reproducibility in the calibration of the jaw position which candidate the method for beam‐matched linacs.…”

Section: Methodsmentioning

confidence: 99%

“…6 For TrueBeam linacs, several publications have suggested using the Electronic Portal Imaging Device (EPID) to evaluate and calibrate the jaw position. 22,23 It has been shown that using…”

Section: D | Jaw Position Calibrationmentioning

confidence: 99%

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Dosimetric and mechanical equivalency of Varian TrueBeam linear accelerators

Ghazal

Södergren

Westermark

et al. 2020

J Applied Clin Med Phys

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To investigate and improve the level of equivalency of Varian TrueBeam linear accelerators (linacs) in energy-, dosimetric leaf gap-(DLG) and jaw calibration. Methods: Eight linacs with four photon energies: 6 MV, 6 MV FFF, 10 MV FFF, and 15 MV, and three electron energies (on two linacs): 6, 9, and 12 MeV were commisioned and beam-matched. Initially, symmetry of lateral profiles was calibrated for maximum field size. Energy-matching was then performed for photons by adjusting diagonal profiles at maximum field size and depth of maximum dose to coincide with the reference linac, and for electrons by matching the range at percentage depth of ionization of 90%, 80%, and 50%. Calibration of DLG was performed for 6 MV and evaluated among the linacs. The relationship between DLG and the Gap value was investigated. A method using electronic portal imaging device (EPID) was developed and implemented for jaw calibration. Results: Symmetry calibration for photons (electrons) was within 1% (0.7%), further improving the vendor's acceptance criteria. Photon and electron energy-matching was within 0.5% and 0.1 mm, respectively. Calibration of DLG was within 0.032 mm among the linacs and utilizing the relationship between DLG and the Gap value resulted in an empirical calibration method which was implemented to simplify DLG adjustment. Using EPID-based method of calibration, evaluation of the jaw-positioning among the linacs for 30 cm × 30 cm field size was within 0.4 mm and in the junction area within 0.2 mm. Dose delivery error of VMAT-plans were at least 99.2% gamma pass rate (1%, 1 mm). Conclusions: High level of equivalency, beyond clinically accepted criteria, of True-Beam linacs could be achieved which reduced dose delivery systematic errors and increased confidence in interchanging patients among linacs.

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Section: Discussioncontrasting

confidence: 98%

Section: Methodsmentioning

confidence: 99%

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Dosimetric and mechanical equivalency of Varian TrueBeam linear accelerators

Ghazal

Södergren

Westermark

et al. 2020

J Applied Clin Med Phys

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“…Junction requirements in the Canadian Partnership for Quality Radiotherapy (CPQR) protocol specify variances in terms of the dosimetry – 5% tolerance and 10% action levels for the dose peak/valley across the junction of the abutting fields – but the reality is this constrains the jaw position's accuracy and precision to be less than half a millimeter . To add to the complexity one often wishes to match jaws that have a 90° collimator rotation between them and the collimator walkout becomes a serious consideration …”

Section: Introductionmentioning

confidence: 99%

Calibrating TrueBeam jaws by considering collimator walkout to improve the dose uniformity at abutting field junctions

Corns

Zhao

2019

J Applied Clin Med Phys

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Jaw positions on a linear accelerator are calibrated to have accurate field size values over the range of jaw positions and to have excellent junctions when matching fields. It is sufficient to have field size accuracy on the order of a millimeter for most clinical applications but good junctions require submillimeter precision and accuracy in the jaw positioning. Presented is a method to measure collimator walkout with the MV imager and a mathematical model to determine an optimal origin for calibrating jaws on the TrueBeam accelerator. The calibration procedure uses the jaw position encoders which are sufficiently accurate and precise enough to achieve a homogeneous junction dose for abutting fields.

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“…6 Electronic portal imaging device (EPID) based methods for asymmetric jaw alignment QA have been recently reported that the methods are efficient and yield precise measurement of the junction gap or overlap. 6,11 It was noted, however, that the junction doses measured with the EPID were different from film due to the nonwater equivalent EPID scattering properties. 6 In addition, to facilitate EPID for precise dose measurements, there are some problems to overcome; nonwater-equivalent response of EPID with field size, backscatter from components of the EPID support arm, and ghosting effects in the portal imager.…”

Section: Introductionmentioning

confidence: 99%