title: Detector comparison for small field output factor measurements in flattening filter free photon beams.
abstract: OBJECTIVE
  The applicability of various detectors for small field dosimetry and whether there are differences in the detector response when irradiated with FF- and FFF-beams was investigated.
  
  
  METHODS
  Output factors of 6 and 10 MV FF- and FFF-beams were measured with 14 different online detectors using field sizes between 10 × 10 and 0.6 × 0.6 cm(2) at a depth of 5 cm of water in isocentric conditions. Alanine pellets with a diameter of 5 and 2.5mm were used as reference dosimeters for field sizes down to 1.2 × 1.2 and 0.6 × 0.6 cm(2), respectively. The ratio of the relative output measured with the online detectors to the relative output measured with alanine was evaluated (referred to as dose response ratio).
  
  
  RESULTS
  The dose response ratios of two different shielded diodes measured with 10 MV FF-beams deviated substantially by 2-3% compared to FFF-beams at a field size of 0.6 × 0.6 cm(2). This difference was less pronounced for 6 MV FF- and FFF-beams. For all other detectors the dose response ratios of FF- and FFF-beams showed no significant difference.
  
  
  CONCLUSIONS
  The dose response ratios of the majority of the detectors agreed within the measurement uncertainty when irradiated with FF- and FFF-beams. Of all investigated detectors, the microDiamond and the unshielded diodes would require only small corrections which make them suitable candidates for small field dosimetry in FF- and FFF-beams.
authors.affiliation: Department of Radiation Oncology, Medical University of Vienna/AKH Wien, Vienna, Austria; Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Vienna, Austria. Electronic address: wolfgang.lechner@meduniwien.ac.at.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lechner
authors.forename: Hugo
authors.initials: H
authors.lastname: Palmans
authors.forename: Lukas
authors.initials: L
authors.lastname: Sölkner
authors.forename: Paulina
authors.initials: P
authors.lastname: Grochowska
authors.forename: Dietmar
authors.initials: D
authors.lastname: Georg
mesh_terms: D000409:Alanine / Q000737:chemistry; D002138:Calibration; D005374:Filtration / Q000295:instrumentation; D010315:Particle Accelerators / Q000295:instrumentation; D019047:Phantoms, Imaging; D017785:Photons; D011874:Radiometry / Q000295:instrumentation*; D035501:Uncertainty
chemical_list: D000409:Alanine
keywords: Alanine; FFF; Flattening filter free; Output factors; Small fields