title: Detector to detector corrections: a comprehensive experimental study of detector specific correction factors for beam output measurements for small radiotherapy beams.
abstract: OBJECTIVE
  The aim of the present study is to provide a comprehensive set of detector specific correction factors for beam output measurements for small beams, for a wide range of real time and passive detectors. The detector specific correction factors determined in this study may be potentially useful as a reference data set for small beam dosimetry measurements.
  
  
  METHODS
  Dose response of passive and real time detectors was investigated for small field sizes shaped with a micromultileaf collimator ranging from 0.6 × 0.6 cm(2) to 4.2 × 4.2 cm(2) and the measurements were extended to larger fields of up to 10 × 10 cm(2). Measurements were performed at 5 cm depth, in a 6 MV photon beam. Detectors used included alanine, thermoluminescent dosimeters (TLDs), stereotactic diode, electron diode, photon diode, radiophotoluminescent dosimeters (RPLDs), radioluminescence detector based on carbon-doped aluminium oxide (Al2O3:C), organic plastic scintillators, diamond detectors, liquid filled ion chamber, and a range of small volume air filled ionization chambers (volumes ranging from 0.002 cm(3) to 0.3 cm(3)). All detector measurements were corrected for volume averaging effect and compared with dose ratios determined from alanine to derive a detector correction factors that account for beam perturbation related to nonwater equivalence of the detector materials.
  
  
  RESULTS
  For the detectors used in this study, volume averaging corrections ranged from unity for the smallest detectors such as the diodes, 1.148 for the 0.14 cm(3) air filled ionization chamber and were as high as 1.924 for the 0.3 cm(3) ionization chamber. After applying volume averaging corrections, the detector readings were consistent among themselves and with alanine measurements for several small detectors but they differed for larger detectors, in particular for some small ionization chambers with volumes larger than 0.1 cm(3).
  
  
  CONCLUSIONS
  The results demonstrate how important it is for the appropriate corrections to be applied to give consistent and accurate measurements for a range of detectors in small beam geometry. The results further demonstrate that depending on the choice of detectors, there is a potential for large errors when effects such as volume averaging, perturbation and differences in material properties of detectors are not taken into account. As the commissioning of small fields for clinical treatment has to rely on accurate dose measurements, the authors recommend the use of detectors that require relatively little correction, such as unshielded diodes, diamond detectors or microchambers, and solid state detectors such as alanine, TLD, Al2O3:C, or scintillators.
authors.affiliation: International Atomic Energy Agency, Vienna International Centre, PO Box 100, 1400 Vienna, Austria.
authors.forename: Godfrey
authors.initials: G
authors.lastname: Azangwe
authors.affiliation: International Atomic Energy Agency, Vienna International Centre, PO Box 100, 1400 Vienna, Austria.
authors.forename: Paulina
authors.initials: P
authors.lastname: Grochowska
authors.affiliation: Department of Radiation Oncology, Medical University Vienna/AKH Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria and Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University Vienna, Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria.
authors.forename: Dietmar
authors.initials: D
authors.lastname: Georg
authors.affiliation: International Atomic Energy Agency, Vienna International Centre, PO Box 100, 1400 Vienna, Austria.
authors.forename: Joanna
authors.initials: J
authors.lastname: Izewska
authors.affiliation: Department of Radiation Oncology, Medical University Vienna/AKH Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria and Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University Vienna, Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria.
authors.forename: Johannes
authors.initials: J
authors.lastname: Hopfgartner
authors.affiliation: Department of Radiation Oncology, Medical University Vienna/AKH Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria and Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University Vienna, Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lechner
authors.affiliation: Center for Nuclear Technologies, Technical University of Denmark, Risø Campus, DK-4000 Roskilde, Denmark.
authors.forename: Claus E
authors.initials: CE
authors.lastname: Andersen
authors.affiliation: Center for Nuclear Technologies, Technical University of Denmark, Risø Campus, DK-4000 Roskilde, Denmark.
authors.forename: Anders R
authors.initials: AR
authors.lastname: Beierholm
authors.affiliation: Center for Nuclear Technologies, Technical University of Denmark, Risø Campus, DK-4000 Roskilde, Denmark.
authors.forename: Jakob
authors.initials: J
authors.lastname: Helt-Hansen
authors.affiliation: National Institute of Radiological Sciences, 4-9-1, Anagawa, Inage-ku, Chiba-shi 263-8555, Japan.
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Mizuno
authors.affiliation: National Institute of Radiological Sciences, 4-9-1, Anagawa, Inage-ku, Chiba-shi 263-8555, Japan.
authors.forename: Akifumi
authors.initials: A
authors.lastname: Fukumura
authors.affiliation: Association for Nuclear Technology in Medicine, 7-16, Nihonbashikodenmacho, chuou-ku, Tokyo 103-0001, Japan.
authors.forename: Kaori
authors.initials: K
authors.lastname: Yajima
authors.affiliation: National Physical Laboratory, Acoustics and Ionising Radiation Division, Teddington TW11 0LW, United Kingdom.
authors.forename: Clare
authors.initials: C
authors.lastname: Gouldstone
authors.affiliation: National Physical Laboratory, Acoustics and Ionising Radiation Division, Teddington TW11 0LW, United Kingdom.
authors.forename: Peter
authors.initials: P
authors.lastname: Sharpe
authors.affiliation: International Atomic Energy Agency, Vienna International Centre, PO Box 100, 1400 Vienna, Austria.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Meghzifene
authors.affiliation: National Physical Laboratory, Acoustics and Ionising Radiation Division, Teddington TW11 0LW, United Kingdom and EBG MedAustron GmbH, Medical Physics Department, A-2700 Wiener Neustadt, Austria.
authors.forename: Hugo
authors.initials: H
authors.lastname: Palmans
mesh_terms: D000388:Air; D000409:Alanine; D000465:Algorithms; D010315:Particle Accelerators; D017785:Photons / Q000627:therapeutic use; D011874:Radiometry / Q000295:instrumentation / Q000379:methods; D011878:Radiotherapy / Q000295:instrumentation* / Q000379:methods*
chemical_list: D000409:Alanine