Origins of the changing detector response in small megavoltage photon radiation fields

Physics in Medicine and Biology
John D FenwickA E Nahum

Abstract

Differences in detector response between measured small fields, f clin, and wider reference fields, f msr , can be overcome by using correction factors [Formula: see text] or by designing detectors with field-size invariant responses. The changing response in small fields is caused by perturbations of the electron fluence within the detector sensitive volume. For solid-state detectors, it has recently been suggested that these perturbations might be caused by the non-water-equivalent effective atomic numbers Z of detector materials, rather than by their non-water-like densities. Using the EGSnrc Monte Carlo code we have analyzed the response of a PTW 60017 diode detector in a 6 MV beam, calculating the [Formula: see text] correction factor from computed doses absorbed by water and by the detector sensitive volume in 0.5  ×  0.5 and 4  ×  4 cm2 fields. In addition to the 'real' detector, fully modelled according to the manufacturer's blue-prints, we calculated doses and [Formula: see text] factors for a 'Z  →  water' detector variant in which mass stopping-powers and microscopic interaction coefficients were set to those of water while preserving real material densities, and for a 'density  →  1' variant in which densities were ...Continue Reading

References

Dec 17, 2008·Medical Physics·R AlfonsoS Vatnitsky
Nov 26, 2009·Medical Physics·Hugo BouchardIwan Kawrakow
Jun 23, 2012·Physics in Medicine and Biology·Alison J D ScottJohn D Fenwick
Aug 9, 2012·Physics in Medicine and Biology·George X Ding, Frances Ding
Mar 22, 2013·Physics in Medicine and Biology·D Czarnecki, K Zink
Oct 1, 2013·Physics in Medicine and Biology·G Cranmer-SargisonD I Thwaites
Mar 20, 2015·Physics in Medicine and Biology·T S A UnderwoodJ D Fenwick
Dec 31, 2016·Physics in Medicine and Biology·Pedro Andreo, Hamza Benmakhlouf
Aug 10, 2017·Physics in Medicine and Biology·Vanessa De CosteGianluca Verona-Rinati

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Citations

Jul 17, 2019·Medical Physics·Ann-Britt SchönfeldHui Khee Looe
May 12, 2020·Physics in Medicine and Biology·Georgios GeorgiouJohn D Fenwick
May 21, 2021·Physics in Medicine and Biology·Vaiva KaveckyteJosé M Fernández-Varea
Oct 7, 2021·Medical Physics·Günther H HartmannKlemens Zink

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