2014
DOI: 10.1088/0031-9155/59/4/911
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Monitor backscatter factors for the Varian 21EX and TrueBeam linear accelerators: measurements and Monte Carlo modelling

Abstract: Linac backscattered radiation (BSR) into the monitor chamber affects the chamber's signal and has to be accounted for in radiotherapy dose calculations. In Monte Carlo (MC) calculations, the BSR can be modelled explicitly and accounted for in absolute dose. However, explicit modelling of the BSR becomes impossible if treatment head geometry is not available. In this study, monitor backscatter factors (MBSFs), defined as the ratio of the charge collected in the monitor chamber for a reference field to that of a… Show more

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Cited by 20 publications
(28 citation statements)
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“…The measured NMU values presented in this work are in agreement with published data measured on similar machine heads and beam types [9]. Furthermore, the estimator of the maximum relative uncertainty of the NMU values reported in this work reveals that this novel methodology has a precision similar to the refined telescopic method presented by Zavgorodni et al…”
Section: Discussionsupporting
confidence: 90%
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“…The measured NMU values presented in this work are in agreement with published data measured on similar machine heads and beam types [9]. Furthermore, the estimator of the maximum relative uncertainty of the NMU values reported in this work reveals that this novel methodology has a precision similar to the refined telescopic method presented by Zavgorodni et al…”
Section: Discussionsupporting
confidence: 90%
“…Recently, Zavgorodni and colleagues have published measured backscatter data from an identical machine head, and for the same photon energies [9]. Their backscatter descriptor, S b , was defined as the inverse of the NMU quantity used in this work.…”
Section: Comparison Of the 3 Methods And Published Datamentioning
confidence: 99%
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“…Depending on the size defined by the upper Y jaw, different amounts of backscattered photons are generated 33 , 34 . A smaller upper jaw (Y) opening induces more backscatter into the monitor chamber, which subsequently results in fewer MUs delivered, producing a smaller OF.…”
Section: Discussionmentioning
confidence: 99%
“…Varian advises the customers to use a C‐series instead although some difference in the backscatter factors between C‐Series and TrueBeam machines can be expected 24. Recently published papers about CBSF show a large difference between the CBSF in Torsti et al16 and the ones published by Sibolt et al25 and Zavgorodni et al24 Sibolt et al25 discusses the increased shielding of the monitor chamber in the treatment head in TrueBeam linacs of with respect to Clinacs. Moreover, linac head geometry is not made available for TB linacs, which makes it impossible to explicitly model the backscatter to the monitor chamber.…”
Section: Discussionmentioning
confidence: 99%