Validating kQ =1.0 assumption in TG51 with PTW 30013 farmer chamber for Varian TrueBeam's 2.5 MV imaging beam

Journal of Applied Clinical Medical Physics
Shelby GrzeticNilendu Gupta

Abstract

AAPM Report 142 recommends and the State of Ohio requires that the imaging dose be quantified in radiotherapy applications. Using the TG51 dose calibration protocol for MV Imaging dose measurement requires knowledge of the kQ parameter for the beam quality and the ionization chamber type under investigation. The %dd(10)x of the Varian TrueBeam 2.5 MV imaging beam falls outside the range of the available data for the calculation of the kQ value. Due to the similarities of the 2.5 MV imaging beam and the 60 Co beam, we and others made the assumption that kQ = 1.0 in TG51 calculations. In this study, we used the TG21 and TG51 calibration protocols in conjunction to validate that kQ = 1.0 for the 2.5 MV imaging beam using a PTW 30013 farmer chamber. Standard measurements for TG51 absolute dosimetry QA were performed at 100 cm SSD, 10 cm depth, 10 × 10 field size, delivering 100 Monitor Units to a waterproof Farmer Chamber (PTW TN30013) for both 2.5 and 6 MV. Both the TG21 and TG51 formalisms were used to calculate the dose to water per MU at dmax (Dw /MU) for the 6 MV beam. The calculated outputs were 1.0005 and 1.0004 cGy/MU respectively. The TG21 formalism was then used to calculate (Dw /MU) for the 2.5 MV imaging beam. This valu...Continue Reading

References

Oct 25, 2001·Journal of Applied Clinical Medical Physics·S H ChoW F Hanson
Oct 9, 2009·Medical Physics·Eric E KleinUNKNOWN Task Group 142, American Association of Physicists in Medicine
Sep 30, 2016·Journal of Applied Clinical Medical Physics·James L GräfeRao F H Khan

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Citations

Nov 2, 2019·Journal of Applied Clinical Medical Physics·William S FerrisZacariah E Labby
Sep 11, 2019·Australasian Physical & Engineering Sciences in Medicine·Martin ButsonRobin Hill

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