title: A radiation quality correction factor k for well-type ionization chambers for the measurement of the reference air kerma rate of (60)Co HDR brachytherapy sources.
abstract: OBJECTIVE
  The aim of this study was to investigate whether a chamber-type-specific radiation quality correction factor kQ can be determined in order to measure the reference air kerma rate of (60)Co high-dose-rate (HDR) brachytherapy sources with acceptable uncertainty by means of a well-type ionization chamber calibrated for (192)Ir HDR sources.
  
  
  METHODS
  The calibration coefficients of 35 well-type ionization chambers of two different chamber types for radiation fields of (60)Co and (192)Ir HDR brachytherapy sources were determined experimentally. A radiation quality correction factor kQ was determined as the ratio of the calibration coefficients for (60)Co and (192)Ir. The dependence on chamber-to-chamber variations, source-to-source variations, and source strength was investigated.
  
  
  RESULTS
  For the PTW Tx33004 (Nucletron source dosimetry system (SDS)) well-type chamber, the type-specific radiation quality correction factor kQ is 1.19. Note that this value is valid for chambers with the serial number, SN ≥ 315 (Nucletron SDS SN ≥ 548) onward only. For the Standard Imaging HDR 1000 Plus well-type chambers, the type-specific correction factor kQ is 1.05. Both kQ values are independent of the source strengths in the complete clinically relevant range. The relative expanded uncertainty (k = 2) of kQ is UkQ = 2.1% for both chamber types.
  
  
  CONCLUSIONS
  The calibration coefficient of a well-type chamber for radiation fields of (60)Co HDR brachytherapy sources can be calculated from a given calibration coefficient for (192)Ir radiation by using a chamber-type-specific radiation quality correction factor kQ. However, the uncertainty of a (60)Co calibration coefficient calculated via kQ is at least twice as large as that for a direct calibration with a (60)Co source.
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, Braunschweig 38116, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Schüller
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, Braunschweig 38116, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Meier
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, Braunschweig 38116, Germany.
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Selbach
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, Braunschweig 38116, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Ankerhold
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods*; D002138:Calibration; D003037:Cobalt Radioisotopes / Q000627:therapeutic use*; D007496:Iridium Radioisotopes / Q000627:therapeutic use; D011874:Radiometry; D035501:Uncertainty
chemical_list: D003037:Cobalt Radioisotopes; D007496:Iridium Radioisotopes