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.     

Direct ion storage dosimetry systems for photon, beta and neutron radiation with instant readout capabilities

The direct ion storage (DIS) dosemeter is a new type of electronic dosemeter from which the dose information for both Hp(10) and Hp(0.07) can be obtained instantly at the workplace by using an electronic reader unit. The number of readouts is unlimited and the stored information is not affected by the readout procedure. The accumulated dose can also be electronically reset by authorised personnel. The DIS dosemeter represents a potential alternative for replacing the existing film and thermoluminescence dosemeters (TLDs) used in occupational monitoring due to its ease of use and low operating costs. The standard version for normal photon and beta dosimetry, as well as a developmental version for neutron dosimetry, have been characterised in several field studies. Two new small size variations are also introduced, including a contactless readout device and a militarised version optimised for field use.     

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.     

A whole-body dosimetry system for personal monitoring based on hot-pressed thin layer TLD

We are introducing a new high-capacity thermoluminescent dosemeter (TLD) system to measure the whole body values of H(p)(10) and H(p)(0.07) from photons for use in individual monitoring services. Small and light-weight badges allow a convenient application in a wide variety of workplaces with photon radiation from 20 keV to at least 7 MeV. The main advantage of this system will be the large capacity of ～ 100,000 dosemeters per month at costs equivalent to the current film monitoring. The hot-pressed thin-layer TL detector (LiF:Mg,Ti) is welded onto an aluminium substrate and provided with a data matrix code for automatic processing. The detector holder has been optimised, that no additional filter is necessary. The new designed TLD reader with readout times <10 s will allow a large throughput and a considerable degree of automation.     

Identification of static exposure of standard dosimetric badge with thermoluminescent detectors

There are three main methods used in individual monitoring: radiographic films, thermoluminescence (TL) and optically stimulated luminescence (OSL). Distinguishing between static (e.g. by leaving it accidentally or purposely in the radiation field) and dynamic exposures can be almost routinely performed for radiographic and OSL methods but is still unsolved for TL detectors. The main aim of this work is to develop a method for identifying static exposures of standard TL detectors at doses which are typical of radiation protection. For this purpose, a new TLD reader equipped with a CCD camera was developed to measure the two-dimensional signal map and not only the total light emitted (as is performed with standard photomultiplier-based TL readers). Standard MCP-N (LiF:Mg,Cu,P) TL pellets of 4.5 mm diameter and 0.9 mm thickness were installed in the standard Rados TL personal badges with special, non-uniform filters and exposed statically to 33 keV X-ray beams at three angles: 0 degrees , 30 degrees and 60 degrees . The detectors were readout in the CCD camera reader and 2-D images were collected. The analysis of these CCD images allows the identification of the static exposure cases and partly the angle of incidence at a dose level of 20 mSv.     

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.     

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.     

Fibre remote optoelectronic gamma dosimetry based on optically stimulated luminescence of Al2O3:C

Optically stimulated luminescence dosimetry (OSL-D) used in conjunction with fibre optics enables a remote measurement of dose, for the purpose of radioprotection in the nuclear industry and in medicine (radiology, radiotherapy). Alumina OSL crystals are used because of their low Z, low fading and optical transparency, which improves the sensitivity. An optoelectronic portable dosemeter has been designed and tested that shows a dose detection of 50 microGy with a 20 metre-long fibre. Following irradiation, all trapped electrons are released under light stimulation while the OSL is integrated to provide dose-equivalent measurements. A compensation technique is designed with the help of the MCNP4b code, so that both angular and photon energy characteristics comply with international standards (CEI 61066) for photon dose equivalent Hp(10). Two sensors are described that allow measurements over a wide solid angle (95% of 4piSr), for photon energies ranging from 15 keV to 3 MeV.     

Comparison on characteristics of radiophotoluminescent glass dosemeters and thermoluminescent dosemeters

The radiophotoluminescent glass dosemeter (RPLGD) system is applicable for measurement of radiation dose of X rays and gamma rays by using radiophotoluminescent glass (silver-activated phosphate glass). When the radiophotoluminescent glass is exposed to ionizing radiation, stable luminescent centres are created. During pulsed ultraviolet laser excitation (337.1 nm) in the reader, the centres emit a radiation induced orange fluorescent light (600-700 nm). This phenomenon is called radiophotoluminescence. This study compared the RPLGD system with lithium fluoride (LiF) thermoluminescence dosimetry system and the results of the study revealed that the RPLGD had not only good basic characteristics for reproducibility of readout value, dose linearity, energy dependence and fading, but also infinite repeatable measurements and could be one of the most important radiation dose measurement instruments.     

Recent advances in dosimetry using the optically stimulated luminescence of Al2O3:C

This paper presents an overview of some very recent developments in optically stimulated luminescence (OSL) dosimetry using aluminium oxide (Al(2)O(3):C), with special emphasis given to the work of the research group at Oklahoma State University. Some of the advances are: (i) the development of a real-time optical fibre system for in vivo dosimetry applied to radiotherapy; (ii) the development of a fibre dosimetry system for remote detection of radiological contaminants in soil; (iii) the characterisation of Al(2)O(3):C in heavy charged particle fields and the study of ionisation density dependence of the OSL from Al(2)O(3):C; and (iv) fast and separate assessment of beta and gamma components of the natural dose rate in natural sediments. These achievements highlight the versatility of the OSL technique associated with the high-sensitivity of Al(2)O(3):C for the development of new dosimetry applications.     

Dose measurement for patients and physicians using a glass dosemeter during endovascular treatment for brain disease

It has been reported that exposure of patients and physicians to radiation from interventional radiological procedures cannot be disregarded. Direct measurement of patient exposure used to be difficult due to possible interference by the detector with the observation of X ray images. Recently, a dosemeter system consisting of small-sized glass chips and a reader which adopts pulsed UV laser stimulation has been developed. Owing to its small size, radiolucency and physical characteristics, direct monitoring of surface dose has become feasible. Dose measurement for patients and physicians during neurointervention was done using the photoluminescence glass dosemeter system. The dose-response of the dosemeter was almost linear over a broad dose range, but its energy dependency was rather high without a filter, the use of which is recommended by the manufacturer to compensate for energy dependency. Variation of sensitivity of about 20% was observed for effective energies of 45-60 keV which are used in neurointervention. In spite of this shortcoming, the photoluminescence glass dosemeter system was judged to be a convenient means for monitoring dose during neurointervention.     

Experimental determination of the dose deposition profile of a 90Sr beta source

Three different methods for characterising the dose deposition profile of a (90)Sr/(90)Y radioactive source are described: GAFChromic film dosimetry, Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL). For the film measurements, GAFChromic film samples were stacked at different depths between polyethylene terephthalate (PET) foils. For TL, the thickness of a TLD-500 dosemeter was gradually reduced by polishing and the TL from chips of different thickness was used in conjunction with a mathematical model based on the exponential attenuation of dose inside the crystal to determine the decay constant for the dose-depth profile. Finally, an OSL reader with confocal stimulation / detection capabilities was used to map the two-dimensional dose distribution in TLD-500 dosemeters as a function of depth. The shapes of the dose deposition profiles obtained from all the investigated methods are in good agreement.     

In situ long-term monitoring system for radioactive contaminants

A long-term in situ subsurface instrument for monitoring radioactive contaminant plumes, as an alternative to soil analysis, is described. A portable, laser-based reader optically stimulates luminescence from sensors, each containing an Al2O3:C dosemeter. The sensors, designed for placement at various subsurface locations around a waste site, are allowed to accumulate dose for a predetermined time that is based on the instrument's minimum detectable dose (MDD). The reader is then attached to the sensor by fibre optic cable to read the accumulated dose; an increase above natural background levels indicating the presence of leaked radioactivity. Based on an MDD of 5 microGy, it is shown that the sensor can measure soil concentrations of 1.85 Bq cm(-3) after an exposure time of 50 h for 137Cs and 67 h for 90Sr/90Y. Discrimination between beta and gamma radiation is possible using an end cap placed over one of the two paired sensors, allowing simultaneous measurement of 137Cs and 90Sr/90Y in a mixed field. The monitor system represents a substantial improvement over quarterly soil sampling because of a greatly increased measurement frequency and the ability to perform measurements reproducibly.     

ENEA personal dosemeters for assessing Hp(10) and Hp(0.07)

Although, at present, neither Italian legislation nor technical protocols require that personal dosimetry is performed to assess Hp(d), the ENEA Individual Monitoring Service (IMS) is able to supply thermoluminescence (TL) whole-body and extremity dosemeters for photon and beta fields, based on LiF(Mg,Cu,P) detectors and these have been fully developed at the ENEA Institute for Radiation Protection (IRP). All irradiation tests have been performed with ISO phantoms and ISO recommended reference radiations at the ENEA-IRP Secondary Standard Dosimetry Laboratory. The whole-body dosemeter contains two LiF(Mg,Cu,P) (GR200) detectors that are filtered differently. One is filtered on both sides by 290 mg.cm-2 mass per area (270 mg.cm-2 Al + 20 mg.cm-2 plastic protective layer); the other is filtered on both sides by a plastic layer of 20 mg.cm-2 mass per area. In photon radiation fields, the maximum uncertainty due to the energy dependence of the response, is +/- 4% for Hp(0.07) in the energy range 13 keV to 202 keV, and +/- 15% for Hp(10) in the range 13 keV to 1.25 MeV. The dosemeter response in terms of Hp(d,alpha) in beta fields has been investigated recently. The results of a EURADOS trial performance test for photon and beta fields are reported and discussed in this paper. The extremity dosemeter currently used at ENEA IMS consists of a GR200 detector glued on a kapton strip identified by a bar code. Its response in terms of Hp(0.07,alpha) has been measured recently and the results are given. Moreover, different dosemeter assemblies have been tested to compare the performances in photon and beta fields. Therefore, the following three constructions have been prepared: (1) an MCP-Ns (8.5 mg.cm-2 mass per area) detector with a Mylar filter of 0.5 mg.cm-2 mass per area; (2) a polyethylene filter of 12 mg.cm-2 mass per area; and (3) a GR200 (210 mg.cm-2 mass per area) detector with a Mylar filter of 0.5 mg.cm-2. Finally, a brief discussion on international and Italian requirements for personal monitoring is given.     

Characteristics and performance of the Sunna high dose dosemeter using green photoluminescence and UV absorption readout methods

Growth in the use of ionising radiation for medical sterilisation and the potential for wide-scale international food irradiation have created the need for robust, mass-producible, inexpensive, and highly accurate radiation dosemeters. The Sunna dosemeter, lithium fluoride injection-moulded in a polyethylene matrix, can be read out using either green photoluminescence or ultraviolet (UV) absorption. The Sunna dosemeter can be mass-produced inexpensively with high precision. Both the photoluminescent and the UV absorption reader are simple and inexpensive. Both methods of analysis display negligible humidity effects, minimal dose rate dependence, acceptable post-irradiation effects, and permit measurements with a precision of nearly 1% 1sigma. The UV method shows negligible irradiation temperature effects from -30 degrees C to +60 degrees C. The photoluminescence method shows negligible irradiation temperature effects above room temperature for sterilisation dose levels and above. The dosimetry characteristics of these two readout methods are presented along with performance data in commercial sterilisation facilities.     

NaCl as a retrospective and accident dosemeter

NaCl is a cheap and widely available material. This study investigated the potential of NaCl in the form of a household salt as a retrospective and accident dosemeter using optically stimulated luminescence (OSL). Samples of the investigated household salt were stimulated using blue light of linearly modulated power. Attention was concentrated on sensitivity, dose dependence of the OSL signal, fading, optimisation of the read-out procedure and application of analytical protocols that do not require a specific calibration. A potential of NaCl as a complementary dosemeter within emergency preparedness was considered. The behaviour of the OSL signal observed was found to be favourable for dosimetry.     

New data on direct ion storage dosemeters

The DIS-1 dosemeter from the Finnish company RADOS is an innovative kind of passive electronic dosemeter for photon and beta radiation. This study examines the 'long-term' linear response behaviour, the calibration and readout accuracy with large samples of 'used' DIS-1 dosemeters especially in the low-dose region, which is of special interest for radiation protection issues. Our measurements prove the adequacy of the DIS-1 dosemeter for long-term-personal dosimetry. The fast and precise readout seems to make the DIS-1 dosemeter an ideal choice for personal dosimetry in low-dose environments.     

Chemical dosimetry system for criticality accidents

Ruder Boskovi? Institute (RBI) criticality dosimetry system consists of a chemical dosimetry system for measuring the total (neutron + gamma) dose, and a thermoluminescent (TL) dosimetry system for a separate determination of the gamma ray component. The use of the chemical dosemeter solution chlorobenzene-ethanol-trimethylpentane (CET) is based on the radiolytic formation of hydrochloric acid, which protonates a pH indicator, thymolsulphonphthalein. The high molar absorptivity of its red form at 552 nm is responsible for a high sensitivity of the system: doses in the range 0.2-15 Gy can be measured. The dosemeter has been designed as a glass ampoule filled with the CET solution and inserted into a pen-shaped plastic holder. For dose determinations, a newly constructed optoelectronic reader has been used. The RBI team took part in the International Intercomparison of Criticality Accident Dosimetry Systems at the SILENE Reactor, Valduc, June 2002, with the CET dosimetry system. For gamma ray dose determination TLD-700 TL detectors were used. The results obtained with CET dosemeter show very good agreement with the reference values.