Analysis of the tandem calibration method for kerma area meters vis Monte Carlo simulations
2011 (English)In: Standards, Applications and Quality Assurance in Medical Radiation Dosimetry (IDOS). Proceedings of an International Symposium held in Vienna, Austria 9-12 November 2010 (2 Volumes), IAEA , 2011, 129-136 p.Conference paper (Refereed)
The IAEA recommends that uncertainties of dosimetric measurements in diagnostic radiology for risk assessment and quality assurance should be less than 7% on the confidence level of 95%. This accuracy is difficult to achieve with kerma area product (KAP) meters currently used in clinics. The reasons range from the high energy dependence of KAP meters to the wide variety of configurations in which KAP meters are used and calibrated. The tandem calibration method introduced by Pöyry, Komppa and Kosunen in 2005 has the potential to make the calibration procedure simpler and more accurate compared to the traditional beam-area method. In this method, two positions of the reference KAP meter are of interest: (a) a position close to the field KAP meter and (b) a position 20 cm above the couch. In the close position, the distance between the two KAP meters should be at least 30 cm to reduce the effect of back scatter. For the other position, which is recommended for the beam-area calibration method, the distance of 70 cm between the KAP meters was used in this study. The aim of this work was to complement existing experimental data comparing the two configurations with Monte Carlo (MC) simulations. In a geometry consisting of a simplified model of the VacuTec 70157 type KAP meter, the MCNP code was used to simulate the kerma area product, PKA, for the two (close and distant) reference planes. It was found that PKA values for the tube voltage of 40 kV were about 2.5% lower for the distant plane than for the close one. For higher tube voltages, the difference was smaller. The difference was mainly caused by attenuation of the X ray beam in air. Since the problem with high uncertainties in PKA measurements is also caused by the current design of X ray machines, possible solutions are discussed.
Place, publisher, year, edition, pages
IAEA , 2011. 129-136 p.
, International Atomic Energy Agency, ISSN 0074-1884 ; Vol. 1
Medical and Health Sciences
IdentifiersURN: urn:nbn:se:liu:diva-75344ISBN: 978-92-0-116210-6OAI: oai:DiVA.org:liu-75344DiVA: diva2:506006
International Dosimetry Symposium on Standards, Applications and Quality Assurance in Medical Radiation Dosimetry (IDOS), IAEA, November 9-12, Vienna, Austria