The 1D lateral dose response functions of photon-dosimetry detectors in magnetic fields-measurement and Monte-Carlo simulation

Physics in Medicine and Biology
Björn DelfsHui Khee Looe

Abstract

The present study is concerned with clinical photon-beam dosimetry at radiotherapy units combined with magnetic resonance imaging devices. Due to the superposed constant magnetic field, the deflections of the secondary electron trajectories by the Lorentz force not only influence the 2D dose distribution, D(x,y), in water phantoms, but furthermore modify the secondary electron transport within the detectors and thereby the detectors' signal profiles, M(x,y), across the photon beams. This second effect can be represented by the lateral dose response function, K(x,y), the convolution kernel transforming D(x,y) into M(x,y) via the convolution M(x,y)  =  D(x,y) * K(x,y). The 1D functions K(x) of a set of commercial gas-filled and solid-state photon-beam detectors were experimentally determined using a slit beam geometry together with a constant, homogeneous magnetic field of up to 1.42 T. As predicted by a recent Monte-Carlo study (Looe et al 2017b Phys. Med. Biol. 62 5131-48), the functions K(x) of these detectors are shown experimentally to be distorted in magnetic field. For the larger Semiflex 3D 31021 chamber, the FWHM value of K(x) decreases from 4.9 mm for the field free (0 T) case to 4.8 mm in 0.35 T and 4.1 mm in 1.42 T ma...Continue Reading

References

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Mar 21, 2012·Physics in Medicine and Biology·A Gago-AriasJ Pardo-Montero
Jan 30, 2013·Zeitschrift für medizinische Physik·Hui Khee LooeBjörn Poppe
Mar 10, 2015·Physics in Medicine and Biology·Charis KontaxisB W Raaymakers
Jul 3, 2016·Medical Physics·V N Malkov, D W O Rogers
Mar 28, 2017·Zeitschrift für medizinische Physik·Elisa BurkeHui Khee Looe

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