Sensitivity and stability of optically stimulated luminescence dosimeters with filled deep electron/hole traps under pre-irradiation and bleaching conditions

Park, So‐Yeon; Choi, Cheol Young; Park, Jong Min; Chun, Minsoo; Han, Ji Hye; Kim, Jung-In

doi:10.1016/j.ejmp.2017.05.057

Cited by 17 publications

(41 citation statements)

References 29 publications

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“…Shallow electron traps are dosimetric traps that are shallow in the band gap, unstable in ambient temperature environments, and will release their trapped charge within a matter of minutes following exposure to ionizing radiation, in the absence of optical stimulation 1,4 . Deep electron traps are classified as a type of dosimetric trap that is filled when the OSLD accumulates a sufficiently high radiation dose and are attributed to changes in the dosimeter’s sensitivity as well as its observed supralinearity 1,4,6 .…”

Section: Introductionmentioning

confidence: 99%

“…The advantage to optically bleaching OSLDs is that one can use a commercially available light source to clear the residual signal stored in the dosimeter, without physically damaging the dosimeter. A crucial disadvantage to optically bleaching OSLDs is its inability to delocalize electrons stored in the deep dosimetric traps 2,4,5,9 and thereby restore the dosimeter's original sensitivity 3 . Adequate depletion of deep traps stored in Al 2 O 3 :C OSLDs require high‐temperature thermal annealing (900°C for 15 min), which is not suitable for nanoDots in particular due to the potential risk of melting the plastic container housing the Al 2 O 3 :C disk 3,10 .…”

Section: Introductionmentioning

confidence: 99%

“…Adequate depletion of deep traps stored in Al 2 O 3 :C OSLDs require high‐temperature thermal annealing (900°C for 15 min), which is not suitable for nanoDots in particular due to the potential risk of melting the plastic container housing the Al 2 O 3 :C disk 3,10 . Previous works investigating the behavior of nanoDots have recommended or used blue LEDs instead of alternatives such as white or green LEDs for rapid clearance of the signal stored in OSLDs through optical bleaching 9,11 but have not accounted for nanoDots irradiated to a sufficiently high‐dose range where supralinearity was reportedly observed (>1 Gy) 4,5 . Optical bleaching using a light source containing blue/UV wavelengths may be problematic regarding the reuse of OSL nanoDots given the observation that UV and blue light stimulation was reported to induce the phototransfer of charge carriers from deep dosimetric traps, via the conduction band, to shallower dosimetric traps in various samples of Al 2 O 3 :C 3,4,10,12 .…”

Section: Introductionmentioning

confidence: 99%

“…Optical bleaching using a light source containing blue/UV wavelengths may be problematic regarding the reuse of OSL nanoDots given the observation that UV and blue light stimulation was reported to induce the phototransfer of charge carriers from deep dosimetric traps, via the conduction band, to shallower dosimetric traps in various samples of Al 2 O 3 :C 3,4,10,12 . The use of a long‐pass filter has been recommended from previous works 4,7 to optically bleach the OSLD while preventing the phototransfer of deep trap charge carriers but may require prohibitively long durations for complete optical bleaching, on the order of several hundreds or thousands of minutes depending on the accumulated dose history of the dosimeter and the irradiance of the bleaching source. This study seeks to expand on prior studies that were referenced by demonstrating that the regeneration of signal in OSLDs is caused by the exposure of the Al 2 O 3 :C disk to blue light, which may last for weeks following their optical bleaching, and to investigate the energy dependence of this phenomenon in nanoDots with prior irradiation history to 6 MV and 220 kV x rays.…”

Section: Introductionmentioning

confidence: 99%

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Preliminary Investigation into the regeneration of luminescent signal in nanoDot OSLDs

Liu

2020

J Applied Clin Med Phys

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Purpose Reuse of optically stimulated luminescent dosimeters (OSLDs) has been suggested in prior works by using a light source to erase the dosimeter’s signal (optical bleaching) and recharacterizing the dosimeter’s sensitivity based on its dose history. However, depending on the wavelength of the bleaching source and the dosimeter’s dose history this may be problematic due to the presence of deep dosimetric traps and the phototransfer mechanism observed in Al2O3. In this work we examine the regeneration of signal in OSL nanoDots, with prior irradiation history, following their bleaching from a light source containing blue wavelengths. Methods Irradiations were performed on 33 nanoDots at a dose range of 5–3000 cGy using 6 MV and 1000–3000 cGy using 220 kV x rays, with three nanoDots irradiated at each dose value. Following their irradiation, nanoDots were bleached using blue light for a period of 1 h. The postbleached signal in nanoDots was measured over a 27‐day period to track any changes in their measured signal due to the migration of charge carriers from deep dosimetric traps to shallower traps of the dosimeter. Results The growth extent and growth rate observed in bleached nanoDots were observed to be dependent on the dosimeter’s accumulated dose history and energy of the radiation source. The 12 nanoDots with prior irradiation history of 500, 1000, 2000, and 3000 cGy from 6 MV x rays exhibit an increase in measured signal that range from 220 to 5229 PMT counts when measured the first day postbleaching to 408–8710 PMT counts when measured on the 27th day postbleaching, which may be substantial depending on the application regarding the dosimeter's reuse. Conclusion These findings caution against the reuse and optical bleaching of nanoDots with prior irradiation history exceeding 100 cGy and demonstrate an energy, accumulated dose, and time dependence in the regeneration of signal in postbleached nanoDots with prior irradiation history.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Preliminary Investigation into the regeneration of luminescent signal in nanoDot OSLDs

Liu

2020

J Applied Clin Med Phys

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“…Small-sized detectors, such as optically stimulated luminescent dosimeters and metal oxide semiconductor fieldeffect transistors (MOSFETs), can be used to measure the surface dose during treatment. [23][24][25][26] The available in vivo dosimeters for eye lenses can be applied to measure the dose on the skin of the eyelids. However, this surface dose does not represent the eye lens dose.…”

Section: Introductionmentioning

confidence: 99%

Contact lens‐type ocular in vivo dosimeter for radiotherapy

et al. 2019

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Purpose This study aimed to (a) develop a contact lens‐type ocular in vivo dosimeter (CLOD) that can be worn directly on the eye and (b) assess its dosimetric characteristics and biological stability for radiation therapy. Methods The molder of a soft contact lens was directly used to create the dosimeter, which included a radiation‐sensitive component — an active layer similar to a radiochromic film — to measure the delivered dose. A flatbed scanner with a reflection mode was used to measure the change in optical density due to irradiation. The sensitivity, energy, dose rate, and angular dependence were tested, and the uncertainty in determining the dose was calculated using error propagation analysis. Sequential biological stability tests, specifically, cytotoxicity and ocular irritation tests, were conducted to ensure the safe application of the CLOD to patients. Results The dosimeter demonstrated high sensitivity in the low dose region, and the sensitivity linearly decreased with the dose. The responses obtained for the 10 and 15 MV photon beams were 1.7% and 1.9% higher compared to the 6 MV photon beam. A strong dose rate dependence was not obtained for the CLOD. Angular dependence was observed from 90° to 180° with a difference in response from 1% to 2%. The total uncertainty in error propagation analysis decreased as a function of the dose in the red channel. For a dose range of 0 to 50 cGy, the total uncertainties for 5, 10, and 50 cGy were 14.2%, 8.9%, and 5%, respectively. Quantitative evaluation using the MTT (3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide) method presented no cytotoxicity. Further, no corneal opacity, iris reaction, or conjunctival inflammation was observed. Conclusions The CLOD is the first dosimeter that can be worn close to the eye. The results of cytotoxicity and irritation tests indicate that it is a stable medical device. The evaluation of dose characteristics in open field conditions shows that the CLOD can be applied to an in vivo dosimeter in radiotherapy.

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Optically stimulated luminescent dosimeters stable response to dose after repeated bleaching

Jursinic

2020

Medical Physics

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To investigate the dose response of optically stimulated luminescent dosimeters (OSLDs), and how this response changes with repeated use, increased accumulated dose, and bleaching light with or without a UV component. To devise a method to stabilize dose response characteristics of OSLDs that are used repeatedly. To decrease measurement uncertainty. Methods: Optically stimulated luminescent dosimeters irradiations were made using a linear accelerator and Ir-192. The OSLDs (InLight nanoDots) dose response was characterized for these various irradiations under the batch, single use, method and the repeated irradiation method. Some nanoDots were preirradiated with hundreds of Gray of dose with Ir-192 gamma rays. Repeated use OSLDs were bleached with lights that had different UV content. A special bleaching light was fabricated and used that had the same spectrum as the light in the OSLD reader. Results: New, never irradiated, nanoDots had their characteristics altered by illumination with bleaching light that had a UV component. Each new nanoDot had unique sensitivity to dose as well as a unique linearity factor, which was supra-linear. NanoDots that were irradiated and bleached repeatedly had changes in low and high dose sensitivity that was altered if the bleaching light had UV in its spectrum. For nanoDots that have been preirradiated with up to 1500 Gy of dose, their dose response was supra-linear for bleaching light without UV content and infra-linear for light with UV content. Preirradiated nanoDots that were bleached with light without UV content had stable dose sensitivity (AE1.5%), stable linearity factor (AE3.5%) for over 10 bleaching cycles, nonlinear response that was quadratic in dose, and dose measurement uncertainty of AE1.4% for 277 measurements. Conclusions: The UV component in bleaching light has an impact on the dose sensitivity characteristics shown by new or repeatedly irradiated nanoDots. Each new nanoDot has a unique sensitivity to dose as well as a unique linearity factor, which was supra-linear. As nanoDots accumulate dose with repeated use they change sensitivity to low and high dose very differently based on the UV content of the bleaching light. For nanoDots that have been preirradiated with hundreds of Gray of dose their dose response was supra-linear for bleaching light without UV content and infra-linear for light that has UV content. NanoDots can be used repeatedly and have stable dose response characteristics if they are preirradiated and bleached with light without UV content. Dose can be measured with an uncertainty of 1.4%, which is a threefold reduction of the uncertainty found with the single use batch method recommended by the manufacturer.

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Sensitivity and stability of optically stimulated luminescence dosimeters with filled deep electron/hole traps under pre-irradiation and bleaching conditions

Cited by 17 publications

References 29 publications

Preliminary Investigation into the regeneration of luminescent signal in nanoDot OSLDs

Preliminary Investigation into the regeneration of luminescent signal in nanoDot OSLDs

Contact lens‐type ocular in vivo dosimeter for radiotherapy

Optically stimulated luminescent dosimeters stable response to dose after repeated bleaching

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