Study of radioluminescence from CaSO4:Eu films for real-time dosimetry

Abstract

Active detectors based on semiconductors and diodes are largely applied for clinical dosimetry, however they present limitations mainly related to complex electronic structure, limited spatial resolution and high cost. Several materials which exhibit thermoluminescence (TL) and optically stimulated luminescence (OSL) also present radioluminescence (RL), as Al2O3:C,Mg. In principle, RL materials can be used in real-time dosimetry as active detectors if the intensity of the RL signal can be associated with the absorbed dose. The sensitive material can be coupled to optical fibers, CCD devices, or other device to collect its light emission. The phosphor CaSO4:Eu has been studied as TL and OSL detector and literature reports good reproducibility, linear dose-response and negligible fading. Previously, CaSO4:Eu OSL films were produced and applied for two-dimensional dose mapping in radiotherapy. Considering the potential application of CaSO4:Eu films for medical applications, in this work we studied the RL emission of CaSO4:Eu films. Firstly we used a Horiba Absorbance and Fluorescence Spectrometer, model Duetta, and obtained the emission spectra of the CaSO4:Eu films, exciting with different wavelenghts and observed two emission centre groups. The first group is at 385 nm, related to Eu2+ and the second group, related to Eu3+ is at 580 nm, 600 nm and 700 nm. Secondly, to study the RL emission from the CaSO4:Eu film, we used a custom made equipment named LUMI22, which has an X-ray tube (Moxtek 50kV) powered and controlled by a standard controller (FTC-200) to irradiate the samples, and a miniature fiber optic spectrometer (Ocean Optics, FLAME-S-XR1-ES) that is used to identify the wavelength of the emitted light (range 200-1050 nm). Results showed a radioluminescent peak at 390 nm, which should be related to Eu2+. The RL sensitivity is (46.1 ± 1.3) 103 counts/Gy. The film does not need thermal or optical treatment and the radioluminescent peak is reproducible. Comparing the RL intensity after 10 consecutive irradiations with the same conditions, the maximum coeficient of variation is 2.5%. The dose response of the RL is linear (R-square 0.9959) from 0.04 to 0.3 Gy. Results show that the CaSO4:Eu film is promissing for use with the RL technique in real-time clinical dosimetry. It should be possible to evaluate dose distributions in real time using the film and a reader with several fiber optics, for example.