title: Radiation hardness of the storage phosphor europium doped potassium chloride for radiation therapy dosimetry.
abstract: OBJECTIVE
  An important property of a reusable dosimeter is its radiation hardness, that is, its ability to retain its dosimetric merits after irradiation. The radiation hardness of europium doped potassium chloride (KC1:Eu2+), a storage phosphor material recently proposed for radiation therapy dosimetry, is examined in this study.
  
  
  METHODS
  Pellet-style KCl:Eu2+ dosimeters, 6 mm in diameter, and 1 mm thick, were fabricated in-house for this study. The pellets were exposed by a 6 MV photon beam or in a high dose rate 137Cs irradiator. Macroscopic properties, such as radiation sensitivity, dose response linearity, and signal stability, were studied with a laboratory photostimulated luminescence (PSL) readout system. Since phosphor performance is related to the state of the storage centers and the activator, Eu2+, in the host lattice, spectroscopic and temporal measurements were carried out in order to explore radiation-induced changes at the microscopic level.
  
  
  RESULTS
  KCl:Eu2+ dosimeters retained approximately 90% of their initial signal strength after a 5000 Gy dose history. Dose response was initially supralinear over the dose range of 100-700 cGy but became linear after 60 Gy. Linearity did not change significantly in the 0-5000 Gy dose history spanned in this study. Annealing high dose history chips resulted in a return of supralinearity and a recovery of sensitivity. There were no significant changes in the PSL stimulation spectra, PSL emission spectra, photoluminescence spectra, or luminescence lifetime, indicating that the PSL signal process remains intact after irradiation but at a reduced efficiency due to reparable radiation-induced perturbations in the crystal lattice.
  
  
  CONCLUSIONS
  Systematic studies of KCl:Eu2+ material are important for understanding how the material can be optimized for radiation therapy dosimetry purposes. The data presented here indicate that KCl:Eu2+ exhibits strong radiation hardness and lends support for further investigations of this novel material.
authors.affiliation: Department of Radiation Oncology, Washington University School of Medicine, 4921 Parkview Place, Campus Box 8224, St. Louis, Missouri 63110, USA.
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Driewer
authors.forename: Haijian
authors.initials: H
authors.lastname: Chen
authors.forename: Andres
authors.initials: A
authors.lastname: Osvet
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Low
authors.forename: H Harold
authors.initials: HH
authors.lastname: Li
mesh_terms: D004307:Dose-Response Relationship, Radiation; D017743:Equipment Reuse; D005063:Europium / Q000528:radiation effects; D006801:Humans; D049449:Luminescence; D019047:Phantoms, Imaging; D011189:Potassium Chloride / Q000528:radiation effects; D011874:Radiometry / Q000379:methods* / Q000706:statistics & numerical data; D011880:Radiotherapy Planning, Computer-Assisted / Q000706:statistics & numerical data; D050397:Radiotherapy, Intensity-Modulated
chemical_list: D005063:Europium; D011189:Potassium Chloride