title: Correction factors for source strength determination in HDR brachytherapy using the in-phantom method.
abstract: For the purpose of clinical source strength determination for HDR brachytherapy sources, the German society for Medical Physics (DGMP) recommends in their report 13 the usage of a solid state phantom (Krieger-phantom) with a thimble ionization chamber. In this work, the calibration chain for the determination of the reference air-kerma rate Ka,100 and reference dose rate to waterDw,1 by ionization chamber measurement in the Krieger-phantom was modeled via Monte Carlo simulations. These calculations were used to determine global correction factors k(tot), which allows a user to directly convert the reading of an ionization chamber calibrated in terms of absorbed dose to water, into the desired quantity Ka,100 or Dw,1. The factor k(tot) was determined for four available (192)Ir sources and one (60)Co source with three different thimble ionization chambers. Finally, ionization chamber measurements on three μSelectron V2 HDR sources within the Krieger-phantom were performed and Ka,100 was determined according to three different methods: 1) using a calibration factor in terms of absorbed dose to water with the global correction factor [Formula: see text] according DGMP 13 2) using a global correction factor calculated via Monte Carlo 3) using a direct reference air-kerma rate calibration factor determined by the national metrology institute PTB. The comparison of Monte Carlo based [Formula: see text] with those from DGMP 13 showed that the DGMP data were systematically smaller by about 2-2.5%. The experimentally determined [Formula: see text] , based on the direct Ka,100 calibration were also systematically smaller by about 1.5%. Despite of these systematical deviations, the agreement of the different methods was in almost all cases within the 1σ level of confidence of the interval of their respective uncertainties in a Gaussian distribution. The application of Monte Carlo based [Formula: see text] for the determination of Ka,100 for three μSelectron V2 sources revealed the smallest deviation to the manufacturer's source certificate. With the calculated [Formula: see text] for a (60)Co source, the user is now able to accurately determine Ka,100 of a HDR (60)Co source via in-phantom measurement. Moreover, using the presented global correction factor [Formula: see text] , the user is able to determine the future source specification quantity Dw,1 with the same in-phantom setup.
authors.affiliation: Department of Radiotherapy and Radiation Oncology, University Hospital Giessen-Marburg, Marburg, Germany. Electronic address: frank.ubrich@uk-gm.de.
authors.forename: Frank
authors.initials: F
authors.lastname: Ubrich
authors.affiliation: current working address: Varian Medical Systems Particle Therapy GmbH, Bergisch-Gladbach, Germany; Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences (THM) Giessen, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Wulff
authors.affiliation: Department of Radiotherapy and Radiation Oncology, University Hospital Giessen-Marburg, Marburg, Germany.
authors.forename: Rita
authors.initials: R
authors.lastname: Engenhart-Cabillic
authors.affiliation: Department of Radiotherapy and Radiation Oncology, University Hospital Giessen-Marburg, Marburg, Germany; Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences (THM) Giessen, Germany.
authors.forename: Klemens
authors.initials: K
authors.lastname: Zink
mesh_terms: D000465:Algorithms; D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods*; D003198:Computer Simulation; D006801:Humans; D008954:Models, Biological; D015233:Models, Statistical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods*; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: Festkörperphantom; HDR brachytherapy; HDR–Brachytherapie; Ionisationskammer; Monte Carlo simulations; Monte-Carlo-Simulationen; Quellenstärke; global correction factor; globaler Korrektionsfaktor; ionization chamber; solid state phantom; source strength