title: Commissioning optically stimulated luminescence in vivo dosimeters for fast neutron therapy.
abstract: OBJECTIVE
  Clinical in vivo dosimeters intended for use with photon and electron therapies have not been utilized for fast neutron therapy because they are highly susceptible to neutron damage. The objective of this work was to determine if a commercial optically stimulated luminescence (OSL) in vivo dosimetry system could be adapted for use in fast neutron therapy.
  
  
  METHODS
  A 50.5 MeV fast neutron beam generated by a clinical neutron therapy cyclotron was used to irradiate carbon doped aluminum oxide (Al2O3:C) optically simulated luminescence dosimeters (OSLDs) in a solid water phantom under standard calibration conditions, 150 cm SAD, 1.7 cm depth, and 10.3 × 10.0 cm field size. OSLD fading and electron trap depletion studies were performed with the OSLDs irradiated with 20 and 50 cGy and monitored over a 24-h period to determine the optimal time for reading the dosimeters during calibration. Four OSLDs per group were calibrated over a clinical dose range of 0-150 cGy.
  
  
  RESULTS
  OSLD measurement uncertainties were lowered to within ±2%-3% of the expected dose by minimizing the effect of transient fading that occurs with neutron irradiation and maintaining individual calibration factors for each dosimeter. Dose dependent luminescence fading extended beyond the manufacturer's recommended 10 min period for irradiation with photon or electron beams. To minimize OSL variances caused by inconsistent fading among dosimeters, the observed optimal time for reading the OSLDs postirradiation was between 30 and 90 min. No field size, wedge factor, or gantry angle dependencies were observed in the OSLDs irradiated by the studied fast neutron beam.
  
  
  CONCLUSIONS
  Measurements demonstrated that uncertainties less than ±3% were attainable in OSLDs irradiated with fast neutrons under clinical conditions. Accuracy and precision comparable to clinical OSL measurements observed with photons can be achieved by maintaining individual OSLD calibration factors and minimizing transient fading effects.
authors.affiliation: Department of Radiation Oncology, University of Washington, Seattle, Washington 98115.
authors.forename: Lori A
authors.initials: LA
authors.lastname: Young
authors.affiliation: Sylvester comprehensive Cancer Center, University of Miami, Miami, Florida 33124.
authors.forename: Fei
authors.initials: F
authors.lastname: Yang
authors.affiliation: Department of Physics, University of Reno, Reno, Nevada 89557.
authors.forename: Davis
authors.initials: D
authors.lastname: Woodworth
authors.affiliation: Department of Physics, University of California, Santa Barbara, California 93106.
authors.forename: Zephyr
authors.initials: Z
authors.lastname: McCormick
authors.affiliation: Department of Radiation Oncology, University of Washington, Seattle, Washington 98115.
authors.forename: George
authors.initials: G
authors.lastname: Sandison
mesh_terms: D005214:Fast Neutrons / Q000627:therapeutic use*; D006801:Humans; D049449:Luminescence; D011874:Radiometry / Q000295:instrumentation*