title: Characterization of a new unshielded diode for small field dosimetry under flattening filter free beams.
abstract: OBJECTIVE
  To characterize the performance of a new unshielded silicon diode (Razor-IBA) for dose measurements in small flattening filter free beams.
  
  
  METHODS
  The Razor has an active volume of 0.6 mm in diameter and 20 µm in length. The detector response stability in measured dose, dose rate, dose per pulse, and dark current were evaluated. The detector response in square fields (0.6-5.0 cm) was determined using PDD curves, axial beam profiles and output ratios. The performances were compared to that of the previously available SFD-IBA and PFD-IBA diodes.
  
  
  CONCLUSIONS
  The Razor short term stability relative to the SFD was much improved (<±0.1% after 1.2 kGy). The linearity was <±1% (0.05-30 Gy range) and the dose rate dependence was <±0.5% (4-24 Gy/min range). The dose per pulse dependence was <±0.7% (0.08-0.21 cGy/pulse range). The PDDs measured with Razor and PFD differed <1%. A larger dark current was observed with increase in dose (0.0025 pA/Gy) compared to the SFD (0.0002 pA/Gy). This characteristic is attributed to an increased concentration of recombination centers. The beam profile showed good agreement with the SFD. Penumbra differences were <±0.3 mm relative to PFD, with a slight overestimation of the tails (<1%), due to the absence of diode shielding. Output ratios were in good agreement for fields up to 5 × 5 cm(2) (<1%).
  
  
  CONCLUSIONS
  The Razor diode has the same spatial resolution and performance reliability as its predecessor (SFD), but exhibits the additional advantage of improved stability. These features make the Razor diode detector a good candidate for small field dosimetry.
authors.affiliation: Medical Physics Service of the Department of Radiation Oncology, Humanitas Research Hospital, Rozzano, Milan, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Reggiori
authors.affiliation: Medical Physics Service of the Department of Radiation Oncology, Humanitas Research Hospital, Rozzano, Milan, Italy. Electronic address: pietro.mancosu@humanitas.it.
authors.forename: Pietro
authors.initials: P
authors.lastname: Mancosu
authors.affiliation: School of Physics, The University of Sydney, Sydney, Australia; Department of Radiation Oncology, Chris O'Brien Lifehouse, Camperdown, Australia.
authors.forename: Natalka
authors.initials: N
authors.lastname: Suchowerska
authors.affiliation: Medical Physics Service of the Department of Radiation Oncology, Humanitas Research Hospital, Rozzano, Milan, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Lobefalo
authors.affiliation: Medical Physics Service of the Department of Radiation Oncology, Humanitas Research Hospital, Rozzano, Milan, Italy.
authors.forename: Antonella
authors.initials: A
authors.lastname: Stravato
authors.affiliation: Medical Physics Service of the Department of Radiation Oncology, Humanitas Research Hospital, Rozzano, Milan, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Tomatis
authors.affiliation: Department of Radiation Oncology, Humanitas Research Hospital, Rozzano, Milan, Italy.
authors.forename: Marta
authors.initials: M
authors.lastname: Scorsetti
mesh_terms: D055615:Electrical Equipment and Supplies; D017785:Photons; D011829:Radiation Dosage; D011835:Radiation Protection; D011874:Radiometry / Q000295:instrumentation*; D035501:Uncertainty
keywords: Radiotherapy; Razor; Small field dosimetry; Unshielded diode