A real-time,fibre optic dosimetry system using Al2O3 fibres

Al2O3:C optical fibres were examined for potential use as real-time luminescence dosemeters for use in radiotherapy applications. The dosimetric properties of the fibres were studied in order to determine their usefulness as luminescence dosemeters. The measurements were performed by connecting the Al2O3:C fibres to a standard fused silica optical fibre and the optically stimulated luminescence (OSL) and radioluminescence (RL) were measured through the fibre. The OSL and RL responses of the Al2O3 fibre probes were measured during irradiation to determine the potential of the Al2O3:C fibres in a real-time fibre optic dosimetry system.     

Influence of the stem effect on radioluminescence signals from optical fibre Al2O3:C dosemeters

This paper analyses the influence of the Cerenkov radiation and other noise sources, the so-called stem effect, on radioluminescence (RL) signals generated in optical fibre Al2O3:C dosemeters used in medical dosimetry. The optical fibre dosemeter consists of a sensitive Al2O3:C crystal coupled to an optical fibre cable that carries the RL and optically stimulated luminescence (OSL) signals generated in the Al2O3:C crystal. During irradiation of the dosemeter, the real-time dose rate can be determined from the RL signal and after irradiation the total dose absorbed is determined from the OSL signal stimulated using a focused green solid-state laser. In particular, the components of the stem effect generated in the fibres were analysed to determine their impact on the RL signal.     

An algorithm for real-time dosimetry in intensity-modulated radiation therapy using the radioluminescence signal from Al2O3:C

Although the radioluminescence (RL) signal from optical fibre Al(2)O(3):C dosemeters used in medical applications is essentially proportional to dose rate, the crystals used so far are imperfect in the sense that their RL sensitivity changes with accumulated dose. A computational algorithm has been developed that corrects for these sensitivity changes. We further report on a new system that effectively separates the RL signal generated in the crystal from fluorescence and Cerenkov emission generated in the optical fibre cable using a gating technique in connection with pulsed linear accelerator radiation beams. The dosimetry system has been used for dose measurements in a phantom during an intensity-modulated radiation therapy (IMRT) treatment with 6 MV photons. The RL measurement results are in excellent agreement (i.e. within 1%) with both the OSL results and the dose delivered according to the treatment planning system. RL signals from Al(2)O(3):C can be used for real-time dose rate measurements with a time resolution of approximately 0.1 s and a spatial resolution only limited by the size of the detector (<0.5 mm).     

Technical performance of the Luxel Al(2)O(3):C optically stimulated luminescence dosemeter element at radiation oncology and nuclear accident dose levels

The dose ranges typical for radiation oncology and nuclear accident dosimetry are on the order of 2-70 Gy and 0.1-5 Gy, respectively. In terms of solid-state passive dosimetry, thermoluminescent (TL) materials historically have been used extensively for these two applications, with silver-halide, leuco-dye and BaFBr:Eu-based films being used on a more limited basis than TL for radiation oncology. This present work provides results on the performance of a film based on an aluminum oxide, Al(2)O(3):C, for these dosimetry applications, using the optically stimulated luminescence (OSL) readout method. There have been few investigations of Al(2)O(3):C performance at radiation oncology and nuclear accident dose levels, and these have included minimal dosimetric and environmental effects information. Based on investigations already published, the authors of this present study determined that overall improvements over film and TLDs for this Al(2)O(3):C OSL technology at radiation oncology and nuclear accident dose levels may include (1) a more tissue-equivalent response to photons compared to X-ray film, (2) higher sensitivity, (3) ability to reread dosemeters and (4) diagnostic capability using small-area imaging. The results of the present investigation indicate that additional favourable performance characteristics for the Al(2)O(3):C dosemeter are a wide dynamic range (0.001-100 Gy), a response insensitive to temperature and moisture over a wide range, negligible dose rate dependence, and minimal change in post-irradiation response. As a radiation detection medium, this OSL phosphor offers an assortment of dosimetry properties that will permit it to compete with current radiation detection technologies such as silver-halide, leuco-dye and photostimulable-phosphor-based films, as well as TLDs.     

Optically stimulated luminescence from Al2O3:C irradiated with relativistic heavy ions.

Optically stimulated luminescence (OSL) from Al2O3:C (ALOC) irradiated with selected heavy ions (4He, 12C, 40Ar, and 56Fe) was examined for discussion on the effectiveness of ALOC for space radiation protection dosimetry. The OSL efficiency on the absorbed dose basis was almost unity for He (LETinfinity x H2O: 2.2 keV x microm(-1)) and decreased with increasing LET for C (14 keV x microm(-1)), Ar (91 keV x microm(-1)), and Fe (198 keV x microm(-1)); a notable reduction greater than 60%, was observed for Fe ions. The linearity in dose response and the angular independence for the heavy ions were fairly good (+/- <15%) Although further experimental studies are clearly necessary, these results suggest that small ALOC chips can be a part of an integrating dosimetry system in future space missions.     

Optically and thermally stimulated luminescence characteristics of MgO:Tb3+

In this paper main optically stimulated luminescence (OSL) and thermoluminescence (TL) characteristics are presented of a newly synthesised material MgO doped with terbium (Tb) developed at the Institute of Nuclear Science, Vinca. A thermally stimulated emission spectrum showed the characteristic lines of Tb3+ in a wide range of wavelengths. The TL sensitivity of the main TL glow peak at 315 degrees C is 1.7 times higher than the TL of Al2O3:C. The highest OSL sensitivity was obtained under green lamp (500-570 nm) stimulation. The fast component in the OSL decay curve is 2.4 times faster than Al2O3:C. The OSL signal is linear with dose up to 10 Gy. The lower limit of detection was found to be 100 microGy. These first results show that the newly synthesised material has some promising properties for the application in radiation dosimetry.     

Aluminium nitrate ceramics: a potential UV dosemeter material

The ceramic material AlN-Y2O3 is proposed as a potential ultraviolet radiation (UVR) dosemeter using optically stimulated luminescence (OSL) and thermally stimulated luminescence (TL). Experimental studies have shown that AIN ceramics exhibit attractive characteristics suitable for practical UV dosimetry applications. The features are: (1) the spectral sensitivity covers the 200-350 nm range, in the UV-B region it is similar to that of human skin; (2) the angular dependence of the incident radiation follows the cosine law; (3) high yields of both UVR-induced OSL and TL signals compared to those of Al2O3:C; and (4) a large dynamic range TL signal (5 orders of magnitude). Although there is relatively high fading, it is demonstrated that AIN is a feasible material for UVR dosimetry using short integration times.     

Optical fibre dosemeter systems for clinical applications based on radioluminescence and optically stimulated luminescence from Al2O3:C

Optical fibre dosemeter systems based on radioluminescence and optically stimulated luminescence (OSL) from carbon-doped aluminium oxide (Al(2)O(3):C) crystals were developed for in vivo real-time dose rate and absorbed dose measurements in radiotherapy and mammography. A technique was also developed for making ultra-small dosemeter probes that can easily be placed inside patients in radiation treatment. These probes have shown excellent properties in both head and neck intensity-modulated radiation therapy treatment and in mammography. The dose-response of the OSL signal for the new optical fibre dosemeter system showed a repeatability within 0.15% at a dose level of 60 mGy when integrated over 100 s. The temperature dependence in the range 0-45 degrees C showed a reproducibility within 1.3% when the OSL signal was integrated over 100 s.     

Uncertainties associated with the use of optically stimulated luminescence in personal dosimetry

This study investigates several sources of uncertainty associated with the application of optically stimulated luminescence (OSL) to personal dosimetry. A commercial OSL system based on Al(2)O(3):C was used for this study. First, it is demonstrated that the concept of repeated evaluation (readout) of the same dosemeter, often referred to as 're-analysis', can introduce uncertainty in the re-estimated dose. This uncertainty is associated with the fact that the re-analysis process depletes some of the populated traps, resulting in a continuous decrease of the OSL signal with each repeated reading. Furthermore, the rate of depletion may be dose-dependent. Second, it is shown that the previously reported light-induced fading in this system is the result of light leaks through miniature openings in the dosemeter badge.     

Multichannel dosemeter and Al2O3:C optically stimulated luminescence fibre sensors for use in radiation therapy: evaluation with electron beams

This article proposes an innovative multichannel optically stimulated luminescence (OSL) dosemeter for on-line in vivo dose verification in radiation therapy. OSL fibre sensors incorporating small Al(2)O(3):C fibre crystals (TLD(500)) have been tested with an X-ray generator. A reproducible readout procedure should reduce the fading-induced uncertainty ( approximately - 1% per decade). OSL readouts are temperature-dependent [ approximately 0.3% K(-1) when OSL stimulation is performed at the same temperature as irradiation; approximately 0.16% K(-1) after thermalisation (20 degrees C)]. Sensor calibration and depth-dose measurements with electron beams have been performed with a Saturne 43 linear accelerator in reference conditions at CEA-LNHB (ionising radiation reference laboratory in France). Predosed OSL sensors show a good repeatability in multichannel operation and independence versus electron energy in the range (9, 18 MeV). The difference between absorbed doses measured by OSL and an ionisation chamber were within +/-0.9% (for a dose of about 1 Gy) despite a sublinear calibration curve.     

Neutron response characterisation of an OSL neutron dosemeter

The neutron response was characterised for Al(2)O(3):C material coated with (6)Li(2)CO(3). Al(2)O(3):C material, an optically stimulated luminescent (OSL) dosemeter, which is sensitive to both photons and beta radiation but is mostly insensitive to neutron radiation. The Al(2)O(3):C material was coated with (6)Li(2)CO(3) to create a material sensitive to neutrons, beta and photon radiation. In this paper, the neutron response of this new OSL material (OSLN) will be compared with various other neutron measurement technologies in laboratory and field environments.     

Optically and thermally stimulated luminescence of KMgF3:Ce3 and NaMgF3:Ce3+

The potentialities of optically stimulated luminescence (OSL) for personal dosimetry of ionising radiation have stimulated the search for new synthetic materials with good dosimetric properties. The sensitivity of two new OSL materials KMgF3 and NaMgF3 doped with Ce3+ ions has been evaluated and found to be of the same order of magnitude as that of Al2O3:C. Several other characteristics have also been investigated. Promising results for KMgF3:Ce are the high sensitivity and the low fading. However, this material suffers from a high self-dose due to the presence of 40K. NaMgF5:Ce is sensitive as well but shows strong fading. Interesting information on the mechanism has been obtained by correlating the signals of OSL and TL. Furthermore, the different bleachabilities under blue LED illumination of the strongly overlapping glow peaks allowed the extraction of one single peak for KMgF3:Ce3+. The results demonstrate new possibilities offered by the combination of TL and OSL.     

A Monte Carlo study of the energy dependence of Al2O3:C crystals for real-time in vivo dosimetry in mammography

In a previous experimental study, a novel method for in vivo dosimetry has been investigated, based on radioluminescence (RL) and optically stimulated luminescence (OSL). However, because of the large difference in atomic composition between the detector material and the breast tissue, relatively large energy dependence in low-energy X-ray beams can be expected. In the present work, the energy dependence of Al2O3:C crystals was modelled with the Monte Carlo code EGSnrc using three types of X-ray spectra. The results obtained (5.6-7.3%) agree with a previously determined experimental result (9%) within the combined standard uncertainty of the two methods. The influence of the size of the crystal on the energy dependence was investigated together with the effect of varying the thickness of the surrounding light-protective material. The results obtained indicate a minor effect owing to the thickness of the light-protective material, and a somewhat larger effect from reducing the diameter of the crystal. The outcome of this study can be used to improve the future design of the RL/OSL dosimetry system for use in mammography.     

The use of optically stimulated luminescence from AL2O3:C in the dosimetry of high-energy heavy charged particle fields

This paper presents two different approaches of quantifying the optically stimulated luminescence (OSL) response of Al(2)O(3):C to high-energy heavy charged particles (HCPs). The OSL efficiency of Al(2)O(3):C exposed to different HCPs is defined as the sensitivity of the material to HCPs normalised by the sensitivity to gamma. In this paper, we investigate the possibility of introducing a 'mean efficiency' eta(mean), which when used in conjunction with the total gamma dose D(gamma) measured for a mixed radiation exposure allows for the determination of the absorbed dose without the need to determine the individual contributions of different types of radiation to the OSL signal. We tested the hypothesis that information regarding the 'mean efficiency' eta(mean) is contained in the shape of the OSL decay curve, using several approaches in the analysis of the OSL data. This analysis was applied to various mixed field irradiations performed at the HIMAC facility, Chiba, Japan. The results of this analysis are discussed.     

CW-OSL measurement protocols using optical fibre Al2O3:C dosemeters

A new system for in vivo dosimetry during radiotherapy has been introduced. Luminescence signals from a small crystal of carbon-doped aluminium oxide (Al2O3:C) are transmitted through an optical fibre cable to an instrument that contains optical filters, a photomultiplier tube and a green (532 nm) laser. The prime output is continuous wave optically stimulated luminescence (CW-OSL) used for the measurement of the integrated dose. We demonstrate a measurement protocol with high reproducibility and improved linearity, which is suitable for clinical dosimetry. A crystal-specific minimum pre-dose is necessary for signal stabilisation. Simple background subtraction only partially removes the residual signal present at long integration times. Instead, the measurement protocol separates the decay curve into three individual components and only the fast and medium components were used.     

Phototransferred thermoluminescence for use in UVB dosimetry

Results are reported of a study of phototransferred thermoluminescence (PTTL) as a potential method for ultraviolet (UV) radiation dosimetry using several different TL materials. The materials studied in depth include Al2O3:C, CaF2:Cu, MgO and MgO:Cu. The experimental features discussed in this paper include the PTTL response as a function of exposure time at 307 nm and the PTTL wavelength dependence over the range 250-450 nm, using a fixed photon flux at the sample. The study confirms the attractive properties of Al2O3:C as a UV dosimetry material, while CaF2:Cu is shown to have potential as a UVC dosemeter.     

Optically stimulated luminescence dosimetry performance of natural Brazilian topaz exposed to beta radiation

Optically stimulated luminescence (OSL) has become the technique of choice in many areas of dosimetry. Natural materials like topaz are available in large quantities in Brazil and other countries. They have been studied to investigate the possibility of use its thermoluminescence (TL) properties for dosimetric applications. In this work, we investigate the possibility of utilising the OSL properties of natural Brazilian topaz in dosimetry. Bulk topaz samples were exposed to doses up to 100 Gy of beta radiation and the integrated OSL as a function of the dose showed linear behaviour. The fading occurs in the first 20 min after irradiation but it is <6% of the integrated OSL measured shortly after exposure. We conclude that natural colourless topaz is a very suitable phosphor for OSL dosimetry.     

Ionisation density dependence of the optically stimulated luminescence dose-response of AL2O3:C to low-energy charged particles

The optically stimulated luminescence (OSL) response of Al2O3:C to high doses of gamma or beta irradiation can be used to predict the response of this material to charged particles as a function of particle fluence, particle energy and/or linear energy transfer (LET). In particular, it is predicted that track interaction effects at high particle fluences should result in linear-sublinear growth of the OSL signal. Similar considerations also predict a dependence of the fluence at which sublinearity starts upon the energy of the particles. In this work the OSL response of Al2O3:C to low-energy charged particles was investigated using protons (1, 2 and 4 MeV), carbon ions (13 MeV) and oxygen ions (10 MeV). The sublinear growth predicted above was qualitatively confirmed, but the energy dependence prediction was not. Furthermore, the efficiency of OSL production in the material after charged particle irradiation, compared to that obtained for gamma irradiation, is determined from the dose-response curves by fitting to a simple saturating exponential function. The efficiency values so obtained using this method are compared with those obtained from a conventional single-point measurement in the linear portion of the curve and found to be in good agreement. In general, the efficiency decreases as the LET of the particle increases. The present data are compared with published data obtained using high-energy charged particles and the results show that the efficiency is not a unique function of LET.     

仿生设计的Al2O3／纤维增强树脂层状复合材料

把贝壳珍珠层的韧化机制和结构机理应用于陶瓷基复合材料的仿生设计中，制备出Ａｌ２Ｏ３／环氧树脂及Ａｌ２Ｏ３／芳纶纤维增强环氧树脂叠层仿珍珠层复合材料。三点弯曲试验表明，与单相Ａｌ２Ｏ３相比，Ａｌ２Ｏ３／环氧树复合材料的断裂功提高２５％，而Ａｌ２Ｏ３／芳纶纤维增强环氧树脂的断裂功提高８０倍Ａｌ２Ｏ３／环氧树脂复合材料的断裂形貌与珍珠层相似，裂缝曲折扩展；而Ａｌ２Ｏ３／芳纶纤维增强环氧树脂复合材料除具有     

Thermal pre-treatment in the OSL dating of quartz: is it necessary?

Thermal treatment before optically stimulated luminescence (OSL) measurement is an important step in all widely accepted OSL dating procedures used with quartz. This is a major constraint on the design of a portable luminescence instrument for estimating ages in the field. Preliminary experiments show that using a standard dating protocol without heating caused a 30-50% underestimation of equivalent dose. This underestimate arises mainly from OSL derived from the 110 degrees C thermoluminescence (TL) trap; because of the thermal instability of this trap, this OSL contribution is only present in unheated laboratory-regenerated signals, but not in the natural signal. An alternative to thermal pre-treatment is investigated, based on the mathematical separation of the stable dosimetry OSL signal from the total OSL; the latter is the sum of signals from several traps, including the 110 degrees C TL trap. Our results show consistency with dose estimates obtained using a standard measurement protocol including pre-heating.