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Z Med Phys. 2017 Sep;27(3):232-242. doi: 10.1016/j.zemedi.2016.10.001. Epub 2017 Mar 21.

Influence of the Integral Quality Monitor transmission detector on high energy photon beams: A multi-centre study.

Author information

1
Department of Radiation Physics, Institute of Oncology, Ljubljana, Slovenia. Electronic address: bcasar@onko-i.si.
2
Lake Constance Radiation Oncology Centre, Singen & Friedrichshafen, Germany.
3
Department of Radiation Oncology, University of Würzburg, Würzburg, Germany.
4
Department of Radiation Oncology, UC Davis Comprehensive Cancer Center, Sacramento, USA.
5
University of Florence, Department of Biomedical Experimental and Clinical Science "M. Serio", Azienda Ospedaliera Universitaria Careggi, Florence, Italy.
6
Department of Radiation Oncology & Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, USA.
7
Department of Radiation Physics, Institute of Oncology, Ljubljana, Slovenia.
8
Christie Medical Physics & Engineering, The Christie NHS Foundation Trust, Withington, Manchester, United Kingdom.
9
Department of Radiation Oncology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.

Abstract

PURPOSE:

The influence of the Integral Quality Monitor (IQM) transmission detector on photon beam properties was evaluated in a preclinical phase, using data from nine participating centres: (i) the change of beam quality (beam hardening), (ii) the influence on surface dose, and (iii) the attenuation of the IQM detector.

METHODS:

For 6 different nominal photon energies (4 standard, 2 FFF) and square field sizes from 1×1cm2 to 20×20cm2, the effect of IQM on beam quality was assessed from the PDD20,10 values obtained from the percentage dose depth (PDD) curves, measured with and without IQM in the beam path. The change in surface dose with/without IQM was assessed for all available energies and field sizes from 4×4cm2 to 20×20cm2. The transmission factor was calculated by means of measured absorbed dose at 10cm depth for all available energies and field sizes.

RESULTS:

(i) A small (0.11-0.53%) yet statistically significant beam hardening effect was observed, depending on photon beam energy. (ii) The increase in surface dose correlated with field size (p<0.01) for all photon energies except for 18MV. The change in surface dose was smaller than 3.3% in all cases except for the 20×20cm2 field and 10MV FFF beam, where it reached 8.1%. (iii) For standard beams, transmission of the IQM showed a weak dependence on the field size, and a pronounced dependence on the beam energy (0.9412 for 6MV to 0.9578 for 18MV and 0.9440 for 6MV FFF; 0.9533 for 10MV FFF).

CONCLUSIONS:

The effects of the IQM detector on photon beam properties were found to be small yet statistically significant. The magnitudes of changes which were found justify treating IQM either as tray factors within the treatment planning system (TPS) for a particular energy or alternatively as modified outputs for specific beam energy of linear accelerators, which eases the introduction of the IQM into clinical practice.

KEYWORDS:

IQM; Linearbeschleuniger; On-line-Dosisüberwachung; Qualitätssicherung; Strahlaufhärtung; Transmission detector; Transmissionsdetektor; beam hardening; linear accelerator; on-line dose monitoring; quality assurance

PMID:
28336006
DOI:
10.1016/j.zemedi.2016.10.001
[Indexed for MEDLINE]

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