Characterization of the optical properties and stability of Presage™ following irradiation with photons and carbon ions.

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. MATERIALS AND 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.