title: Characterization of the optical properties and stability of Presage™ following irradiation with photons and carbon ions.
abstract: BACKGROUND
  The on-going development of both intensity-modulated radiotherapy (IMRT), including the more recent intensity-modulated arc therapy, as well as particle beam therapy, has created a clear need for accurate verification of dose distributions in three dimensions (3D). Presage™ is a new 3D dosimetry material that exhibits a radiochromic response when exposed to ionizing radiation. In this study we have 1) developed an improved optical set-up for measurements of changes in OD of Presage™ point dosimeters, 2) investigated the dose response of Presage™ for photons and carbon ions in the therapy range, 3) investigated the dose response of Presage™ for photons in the kGy range and 4) investigated the fading (i.e. bleaching) of Presage™ postirradiation.
  
  
  METHODS
  Presage™ was examined in 1 × 1 × 4.5 cm(3) optical cuvettes; a cuvette holder assured accurate repositioning, and the optical setup included a reference detector to take into account laser intensity fluctuations. The cuvettes were measured pre- and postirradiation for a two week period.
  
  
  RESULTS
  A linear response was observed between dose and optical response between 0 Gy and 100 Gy for γ-radiation from Co-60 and for carbon ions (both plateau and SOBP) from 0 to 20 Gy. The dosimeter was found to have a saturation dose of approximately 100 Gy for photons. A linear energy transfer (LET) effect was not observed in the dose response of different LET radiation. The postirradiation change in optical fading was found to be 0.5% ΔOD/day.
  
  
  CONCLUSIONS
  Our study shows that Presage™ remains a dosimeter of interest for radiation therapy with other particles as well as photons in the therapy dose range.
authors.affiliation: Department of Medical Physics, Aarhus University Hospital, Aarhus, Denmark. esbeyate@rm.dk
authors.forename: Esben S
authors.initials: ES
authors.lastname: Yates
authors.forename: Peter
authors.initials: P
authors.lastname: Balling
authors.forename: Jørgen B B
authors.initials: JB
authors.lastname: Petersen
authors.forename: Mehrnaz N
authors.initials: MN
authors.lastname: Christensen
authors.forename: Peter S
authors.initials: PS
authors.lastname: Skyt
authors.forename: Niels
authors.initials: N
authors.lastname: Bassler
authors.forename: Franz-Joachim
authors.initials: FJ
authors.lastname: Kaiser
authors.forename: Ludvig P
authors.initials: LP
authors.lastname: Muren
mesh_terms: D002244:Carbon; D003037:Cobalt Radioisotopes; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D055095:Optics and Photonics; D019047:Phantoms, Imaging; D017785:Photons; D011834:Radiation Monitoring / Q000295:instrumentation*; D011874:Radiometry; D014867:Water
chemical_list: D003037:Cobalt Radioisotopes; D014867:Water; D002244:Carbon