Open AccessIon recombination correction factors ( P ion ) for Varian TrueBeam high‐dose‐rate therapy beams
Author(s) -
Kry Stephen F.,
Popple Richard,
Molineu Andrea,
Followill David S.
Publication year - 2012
Publication title -
journal of applied clinical medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.83
H-Index - 48
ISSN - 1526-9914
DOI - 10.1120/jacmp.v13i6.3803
Subject(s) - truebeam , ion , physics , ionization chamber , atomic physics , optics , linear particle accelerator , beam (structure) , ionization , quantum mechanics
Ion recombination is approximately corrected for in the Task Group 51 protocol byP ion, which is calculated by a two‐voltage measurement. This measurement approach may be a poor estimate of the true recombination, particularly ifP ionis large (greater than 1.05). Concern exists thatP ionin high‐dose‐per‐pulse beams, such as flattening filter free (FFF) beams, may be unacceptably high, rendering the two‐voltage measurement technique inappropriate. Therefore,P ionwas measured for flattened beams of 6, 10, 15, and 18 MV and for FFF beams of 6 and 10 MV. The values for the FFF beams were verified with 1/V versus 1/Q curves (Jaffé plots).P ionwas also measured for electron beams of 6, 12, 16, 18, and 20 MeV on a traditional accelerator, as well as on the high‐dose‐rate Varian TrueBeam accelerator. The measurements were made at a range of depths and with PTW, NEL, and Exradin Farmer‐type chambers. Consistent with the increased dose per pulse,P ionwas higher for FFF beams than for flattening filter beams. However, for all beams, measurement locations, and chambers examined,P ionnever exceeded 1.018. Additionally,P ionwas always within 0.3% of the recombination calculated from the Jaffé plots. We conclude that ion recombination can be adequately accounted for in high‐dose‐rate FFF beams usingP iondetermined with the standard two‐voltage technique. PACS numbers: 87.56.‐v, 87.56.Da