TY - JOUR
T1 - Radiation hardness of the storage phosphor europium doped potassium chloride for radiation therapy dosimetry
AU - Driewer, Joseph P.
AU - Chen, Haijian
AU - Osvet, Andres
AU - Low, Daniel A.
AU - Li, H. Harold
N1 - Funding Information:
This work was supported in part by NIH Grant Nos. R21CA131690 and R01CA148853. JPD was also supported in part by the Nuclear Science and Engineering Institute of the University of Missouri under a Graduate Assistance in Areas of National Need Fellowship funded by the Department of Education. The authors thank Buck Rogers, Girdhar Sharma, and Dinesh Thotala for coordinating the use of the 137 Cs irradiator, Baozhou Sun and Logan Ice for technical assistance, and Paul Leblans and Luc Struye (AGFA HealthCare, Belgium) for providing protective coatings. TABLE I. Signal stability with cumulated dose. Dosimeters were irradiated to several dose levels and the signal stability 13 h after irradiation was examined according to a procedure described in Ref. 3 . Signal stability remained largely unchanged after irradiation to greater than 5000 Gy history. Dose history (Gy) 0 144 630 1770 3000 5000 Signal stability (%decrease/h) 0.24 ± 0.04 0.17 ± 0.06 0.13 ± 0.06 0.13 ± 0.03 0.14 ± 0.05 0.16 ± 0.08 FIG. 1. Sensitivity with cumulated dose. A KCl:Eu 2+ dosimeter was given 200 cGy to establish its zero dose history sensitivity, given escalating doses, bleached, and checked for sensitivity at 200 cGy. An initial increase in sensitivity up to 3000 Gy is followed by a gradual decrease. 90% of initial sensitivity remains after 5000 Gy history. Error bars represent the standard error of repeated measurements. FIG. 2. Response with cumulated dose up to 200 Gy. Dose response curves at various dose histories were obtained and plotted, normalized to 200 cGy. The dose response initially shows supralinear behavior but becomes more linear with dose history. The inset displays the percent deviation of the measured data from a linear model. Error bars represent the standard error of repeated measurements. FIG. 3. Response with cumulated dose up to 5000 Gy. Dose response curves at various dose histories were obtained and plotted, normalized to 500 cGy. A linear dose response holds up to 5000 Gy. Error bars represent the standard error of repeated measurements. FIG. 4. Reset of sensitivity curve with annealing procedure. Chips with 5000 Gy dose history were annealed in a laboratory furnace at 710 °C for 3 h in air. Dose response at points of 100, 300, and 500 cGy were obtained and compared with chips with no annealing procedure. After annealing, the dose response returns to the supralinear behavior. Error bars represent the standard error of repeated measurements. FIG. 5. PSL stimulation spectra with cumulated dose. Stimulation wavelength was varied while collecting PSL at 420 nm (see text). The maximum stimulation efficiency for photostimulated luminescence remained constant at 560 nm with cumulated dose. FIG. 6. PSL emission spectra with cumulated dose. KCl:Eu 2+ dosimeters were stimulated while varying the collection wavelength (see text). The dosimeters emit intense photostimulated luminescence centered at 420 nm, which remained constant with dose history. FIG. 7. PL spectra with cumulated dose. Broad-band UV light was used to simulated the KCl:Eu 2+ dosimeters to emit photoluminescence. The peak of the photoluminescence spectrum remained nearly constant at 420 nm, indicating that little changes in the vicinity of the activator have occurred with dose. FIG. 8. Luminescence lifetime with cumulative dose. A 308 nm eximer laser was used to excite KCl:Eu 2+ PL in dosimeters with dose histories up to 5000 Gy. The PL was sampled during its decay and plotted on a log scale. PL lifetime remained nearly constant at 1.2 μs within experimental uncertainty.
PY - 2011/8
Y1 - 2011/8
N2 - Purpose: 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 (KCl: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:Eu 2 exhibits strong radiation hardness and lends support for further investigations of this novel material.
AB - Purpose: 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 (KCl: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:Eu 2 exhibits strong radiation hardness and lends support for further investigations of this novel material.
KW - IMRT
KW - dosimeter
KW - storage phosphor
UR - http://www.scopus.com/inward/record.url?scp=79961084401&partnerID=8YFLogxK
U2 - 10.1118/1.3611043
DO - 10.1118/1.3611043
M3 - Article
C2 - 21928642
AN - SCOPUS:79961084401
SN - 0094-2405
VL - 38
SP - 4681
EP - 4688
JO - Medical physics
JF - Medical physics
IS - 8
ER -