Monitoring Dosimeter Research Articles

Use of real-time electronic extremity dosimeters for monitoring and optimisation of radiopharmacy technique

Radiopharmacy staff members are subject to extremity radiation doses, particularly to the fingertips. Dosemeters, such as, thermoluminescent detectors (TLDs) are currently used for monitoring fingertip doses. This study aimed to use real-time dosemeters to monitor radiopharmacy extremity doses to identify specific procedural steps associated with higher fingertip doses and, subsequently, reduce dose through promotion of optimised radiation protection practises. Five radiopharmacy operators were monitored using an ED3 active extremity dosemeter with a detector attached to each tip of the index fingers. Dose rate and accumulated dose data were matched to the handled radioactivity data, of99mTc-labelled radiopharmaceuticals only, with the dose per activity (μSv MBq-1) calculated for each step. Once baseline dose data was established, an educational session identified technique adjustments toward improved radiation protection. A subsequent monitored session was undertaken with the dose data compared to quantify changes in operator doses. Radiopharmacy steps which significantly contributed to extremity doses were identified. The average accumulated dose per activity across all procedural steps for the99mTc-labelled radiopharmaceuticals for all operators before the educational session was 0.042 ± 0.045μSv MBq-1and 0.042 ± 0.041μSv MBq-1(n= 89) for non-dominant and dominant index fingertips, respectively, and 0.030 ± 0.044μSv MBq-1and 0.031 ± 0.032μSv MBq-1(n= 97), respectively, afterwards. Overall, there was an average 40.7% reduction in the total extremity dose received after the educational session. Real-time electronic extremity dosemeters for monitoring radiopharmacy extremity dose presented as a useful tool for incorporation into radiation protection education and training, towards optimised radiopharmacy technique.

The possibility of using the DKS-AT1123 dosimeter for radiation monitoring of medical electron accelerators with the energy of more than 10 MeV

In the Russian Federation, there is a constant increase in the number of radiation medical installations with electron accelerators. Over the past 4 years, their number has increased 2.5 times. These installations contain pulsed electron accelerators that generate pulsed bremsstrahlung radiation with a maximum energy from 6 to 21 MeV. Currently, there are no devices designed for dosimetry of the pulsed photon radiation with energy of more than 10 MeV in the state register of measuring instruments of the Russian Federation. The most widely used radiation monitoring device for pulsed electron accelerators is the DKS-AT1123 X-ray and gamma radiation dosimeter designed for dosimetry of pulsed bremsstrahlung radiation with an energy of up to 10 MeV. The purpose of this work is to evaluate the possibility of using this device for dosimetry of pulsed bremsstrahlung radiation with a maximum energy of up to 20 MeV. The authors calculated the energy spectra of bremsstrahlung radiation for a point source with a maximum energy of 20 MeV behind flat concrete screens with a thickness of 1 m, 2 m and 3 m by the Monte Carlo method using the GEANT4 calculation program. The energy dependence of the registration efficiency of the DKS-AT1123 dosimeter was extrapolated to the energy range of 10–50 MeV in the kerma-approximation without taking into account the energy transfer by secondary electrons. It was assumed that it corresponds to the energy dependence of the total mass attenuation coefficient for the absorbed energy of gamma quanta in water. Using conversion coefficients for converting the fluence of monoenergetic photons into the effective dose rate at an anterior-posterior radiation incidence on the human body, real dose rates were calculated, and using the energy dependence of the dosimeter readings, the predicted results of measuring the unit dose rate with the DKS-AT1123 dosimeter behind a concrete protection with a thickness of 1, 2 and 3 m were obtained. It is shown that the maximum expected underestimation of the measurement results will not exceed 40% and practically does not depend on the thickness of the concrete shield in the thickness range from 1 to 3 m. To account for this underestimation, it is necessary to use the value of additional measurement error due to the energy dependence of the sensitivity of this device for the photon radiation energy of more than 10 MeV, equal to 70%. This makes it possible to use the measurement results obtained using this dosimeter to adequately characterize the state of radiation safety during operation of pulsed electron accelerators with a maximum energy of up to 20 MeV. It is possible to use a correction factor to the measurement results equal to 1.63 ±0.04 to compensate for this underestimation. The proposed approach can be used to create a methodology for using this dosimeter for radiation monitoring of medical electron accelerators with the energy of up to 20 MeV, if there are correction factors for radiation protection configurations and radiation energies encountered in practice.

Monitoring beam charge during FLASH irradiations

In recent years, FLASH irradiation has attracted significant interest in radiation research. Studies have shown that irradiation at ultra-high dose rates (FLASH) reduces the severity of toxicities in normal tissues compared to irradiation at conventional dose rates (CONV), as currently used in clinical practice. Most pre-clinical work is currently carried out using charged particle beams and the beam charge monitor described here is relevant to such beams. Any biological effect comparisons between FLASH and CONV irradiations rely on measurement of tissue dose. While well-established approaches can be used to monitor, in real time, the dose delivered during CONV irradiations, monitoring FLASH doses is not so straightforward. Recently the use of non-intercepting beam current transformers (BCTs) has been proposed for FLASH work. Such BCTs have been used for decades in numerous accelerator installations to monitor temporal and intensity beam profiles. In order to serve as monitoring dosimeters, the BCT output current must be integrated, using electronic circuitry or using software integration following signal digitisation. While sensitive enough for FLASH irradiation, where few intense pulses deliver the requisite dose, the inherent insensitivity of BCTs and the need for a wide detection bandwidth makes them less suitable for use during CONV “reference” irradiations. The purpose of this article is to remind the FLASH community of a different mode of BCT operation: direct monitoring of charge, rather than current, achieved by loading the BCT capacitively rather than resistively. The resulting resonant operation achieves very high sensitivities, enabling straightforward monitoring of output during both CONV and FLASH regimes. Historically, such inductive charge monitors have been used for single pulse work; however, a straightforward circuit modification allows selective resonance damping when repetitive pulsing is used, as during FLASH and CONV irradiations. Practical means of achieving this are presented, as are construction and signal processing details. Finally, results are presented showing the beneficial behaviour of the BCT versus an (Advanced Markus) ionisation chamber for measurements over a dose rate range, from <0.1 Gys−1 to >3 kGys−1.

A machine learning approach for correcting glow curve anomalies in CaSO4:Dy-based TLD dosimeters used in personnel monitoring

The study presents a novel approach to analysing the thermoluminescence (TL) glow curves (GCs) of CaSO4:Dy-based personnel monitoring dosimeters using machine learning (ML). This study demonstrates the qualitative and quantitative impact of different types of anomalies on the TL signal and trains ML algorithms to estimate correction factors (CFs) to account for these anomalies. The results show a good degree of agreement between the predicted and actual CFs, with a coefficient of determination greater than 0.95, a root mean square error less than 0.025, and a mean absolute error less than 0.015. The use of ML algorithms leads to a significant two-fold reduction in the coefficient of variation of TL counts from anomalous GCs. This study proposes a promising approach to address anomalies caused by dosimeter, reader, and handling-related factors. Furthermore, it accounts for non-radiation-induced TL at low dose levels towards improving the dosimetric accuracy in personnel monitoring.

Studies of OSL properties of alkali- and rare earth-doped BeO based novel dosimeters for applications in external beam radiotherapy

This study aims to assess the feasibility of a novel Beryllium Oxide (BeO) based ceramics to be used as optically stimulated luminescence (OSL) dosimeters for monitoring of high-energy beams used in radiotherapy. The BeO ceramic dosimeters doped with alkali and rare earth metals (BeO:Na5%,Ce0.005%,Tb0.05%, BeO:Na5%,Ce0.01%,Er0.01%, and BeO:Na5%,Ce0.01%,Dy0.01%) were fabricated in pellet forms, and their luminescence responses were measured at the virtual water phantom interfaces for various field sizes of a 6 MV flattening filter-free photon beam of Varian LINAC. The OSL dosimeter's performance has been confirmed their practical usefulness as in vivo dosimeters in radiotherapy clinics. The provided dose estimates were validated using varying X-ray energies and doses, typically employed for actual medical radiotherapy systems. Our results indicated that the studied dosimeters rendered an almost linear response in the dose range of 0.05 Gy–20 Gy delivered from the 6 MV X-ray beam. Fading of the stored OSL was found to be less than 5% after a short storage period. The dependencies of OSL responses concerning beam energy, dose rate, irradiation angle, depth, and field size are all found to be supportive of the successful utilization of the BeO OSLDs in clinical environments.

Assessment of the Occupational Radiation Dose from a Handheld Portable X-ray Unit During Full-mouth Intraoral Dental Radiographs in the Dog and the Cat - A Pilot Study.

Occupational radiation protection is an important consideration in small animal clinics world-wide. With the increased use of portable handheld X-ray devices in veterinary dentistry, concerns related to occupational radiation protection are being raised. Annual occupational dose limits for dental workers are expressed as Total Dose Equivalent (TDE) or Effective Dose. The permitted TDE can vary depending on the anatomical region, ranging from 50 millisieverts (mSv) for the external whole body exposure dose to 500 mSv for external exposure of the skin or an extremity. Although several studies have been performed in human dentistry to establish the amount of backscatter radiation produced using portable handheld X-ray devices, no similar research has been conducted in veterinary dentistry. This study aimed to determine the TDE while acquiring a full mouth intraoral radiograph set in dogs and cats and to estimate the TDE for a handheld X-ray device's operator. For this, the backscatter radiation dose recorded by three sets of monitoring dosimeters located in strategic anatomical areas of the operator was assessed after taking one hundred intraoral radiographs in each group. The study concluded that the backscatter radiation levels were far below the permitted annual occupational doses in the three patient groups of this study. Even though the portable handheld X-ray unit was demonstrated to be a safe dental radiographic unit regarding backscattering radiation, the operator's eye, ovary, and breast regions were exposed to unnecessary radiation.

A swallowable X-ray dosimeter for the real-time monitoring of radiotherapy.

Monitoring X-ray radiation in the gastrointestinal tract can enhance the precision of radiotherapy in patients with gastrointestinal cancer. Here we report the design and performance, in the gastrointestinal tract of rabbits, of a swallowable X-ray dosimeter for the simultaneous real-time monitoring of absolute absorbed radiation dose and of changes in pH and temperature. The dosimeter consists of a biocompatible optoelectronic capsule containing an optical fibre, lanthanide-doped persistent nanoscintillators, a pH-sensitive polyaniline film and a miniaturized system for the wireless readout of luminescence. The persistent luminescence of the nanoscintillators after irradiation can be used to continuously monitor pH without the need for external excitation. By using a neural-network-based regression model, we estimated the radiation dose from radioluminescence and afterglow intensity and temperature, and show that the dosimeter was approximately five times more accurate than standard methods for dose determination. Swallowable dosimeters may help to improve radiotherapy and to understand how radiotherapy affects tumour pH and temperature.

Single Institute Experience – Linear Accelerator Based Total Body Irradiation Using Volumetric Modulated Arc Therapy Planning in Standard Size Linear Accelerator Room

<h3>Purpose/Objective(s)</h3> To share experience of linear accelerator based total body irradiation (TBI) with volumetric modulated arc therapy (VMAT) in a standard size linear accelerator room <h3>Materials/Methods</h3> 30 patients aged 2-18 years (between 2018-2021) were treated with TBI as conditioning for bone marrow transplant (BMT)using VMAT based plan on our linear accelerator in a standard sized linear accelerator room. Indication of BMT was – acute lymphoblastic leukemia, acute myelogenous leukemia, chronic myeloid leukemia, myelodysplasia, aplastic anemia etc. Patient selection involved assessment regarding need of anesthesia, details of previous radiation, details of conditioning regimen for scheduling, organs dysfunction, adequate counselling and written consent from parents. With or without anesthesia, patients were immobilized using full body vacloc, head rest, brain orfit cast and knee rest. Position was supine, hands by side. Both head first (HF) and feet first (FF) scans were acquired if body length was more than 120 cm (for 120 cm, HF scan alone was acquired). A wire was placed on thigh to aid fusion of HF and FF scans for plan evaluation. Fiducials at three levels and optically stimulated luminescent dosimeter for dose monitoring were placed. Dose was 2-4 Gy single fraction and 12-13.2Gy/6 fractions (twice daily over 3 days, with 6 hours gap) based on chemotherapy conditioning regimen- delivered to 14 and 16 patients respectively. The planning objective was 90-100% coverage and dose max less than 120%. For multifraction plans, target was mean dose to lungs and kidney less than 10 Gy and 8Gy respectively. VMAT plans were generated with 3-5 iso-centers with fixed couch vertical and lateral values and changing longitudinal value, ensuring only longitudinal couch movement. Plan was made using 6MV energy and 5-9 arcs and 3 cm overlap between fields (avoid over joints to prevent effusion and over lungs to reduce lung dose) <h3>Results</h3> Mean PTV V95 – 93% (92-96%), Dmax – 115% mean (109%-120%). Mean lung dose (for 12-13.2Gy plans) was 9.4Gy/ (9-10 Gy), kidney mean dose was 7.8Gy (7.5-8 Gy). Mean monitor units in the plans were 1120 for complete arc and 690 for partial arcs. Treatment was delivered in strict aseptic precautions, under cover of steroids and antiemetics - in presence of radiation oncologist and physicist. Cone beam CT scan was used for position verification before and after treatment. The mean duration of treatment was 75 mins (range 60-90 minutes). 18 patients had grade 2 nausea and vomiting, one had knee joint effusion. No other side effects were reported. All transplants were successful except one reported graft versus host disease. <h3>Conclusion</h3> The procedure needs careful planning and delivery. It is feasible and possible to deliver TBI using VMAT in a standard sized linear accelerator room and should be offered to patients requiring the same.

Effects of high ambient temperature on the accuracy of thermoluminescent dosimeters for environmental monitoring

Thermoluminescence dosimeters (TLDs) are widely used for both personal and environmental dosimetry. TLDs should have high accuracy under different conditions. The TL signal can drop over time because of fading (loss of signal due to thermally induced recombination of trapped charriers), thus leading to underestimation of the irradiation dose. The Saudi climate is extremely hot for most of the year, which could significantly affect TLD measurements. Therefore, the effect of ambient temperature, storage time and irradiation dose were investigated both in laboratory controlled-temperature conditions and field experiments, for two commercial dosimeters: Harshaw (TLD-100H™) and RADCARD (MCP-N™), which are used for environmental monitoring. The irradiated TLDs were exposed to a range of ambient temperatures (25 °C–65 °C) then stored for 30, 60, and 90 days. A signal fading due to increasing ambient temperature and storage time was generally observed. MCP-N shows good stability and is less responsive to increasing ambient temperature compared to TLD-100H. TLD-100H is less affected by storage time compared to MCP-N. Irradiation doses play a role in TL signal fading, and TLDs irradiated with 5 mSv have a higher rate of loss compared to those irradiated with 2 mSv in all TLD types. The obtained results permitted to conclude that all TLD types used in this study suffer from TL signal fading, and its degree varies between TLD types.

What Is Worth Knowing in Interventional Practices about Medical Staff Radiation Exposure Monitoring: A Review of Recent Outcomes of EURADOS Working Group 12

EURADOS (European Radiation Dosimetry Group) Working Group 12 (WG12) SG1 activities are aimed at occupational radiation protection and individual monitoring in X-ray and nuclear medicine practices. In recent years, many studies have been carried out in these fields, especially for interventional radiology and cardiology workplaces (IC/IR). The complexity of the exposure conditions of the medical staff during interventional practices makes the radiation protection and monitoring of the exposed workers a challenging task. The scope of the present work is to review some of the main results obtained within WG12 activities about scattered field characterization and personal dosimetry that could be very useful in increasing the quality of radiation protection of the personnel, safety, and awareness of radiation risk. Two papers on Monte Carlo modelling of interventional theater and three papers on active personal dosimeters (APDs) for personnel monitoring were considered in the review. More specifically, Monte Carlo simulation was used as the main tool to characterize the levels of exposure of the medical staff, allowing to determine how beam energy and direction can have an impact on the doses received by the operators. Indeed, the simulations provided information about the exposure of the operator’s head, and the study concluded with the determination of an eye-lens protection factor when protection goggles and a ceiling shielding are used. Moreover, the review included the results of studies on active personal dosimeters, their use in IC/IR workplaces, and how they respond to calibration fields, with X-ray standard and pulsed beams. It was shown that APDs are insensitive to backscatter radiation, but some of them could not respond correctly to the very intense pulsed fields (as those next to the patient in interventional practices). The measurements during interventional procedures showed the potential capability of the employment of APDs in hospitals.

Gold coated contact lens-type ocular in vivo dosimeter (CLOD) for monitoring of low dose in computed tomography: A Monte Carlo study.

This study reports a sensitivity enhancement of gold-coated contact lens-type ocular in vivo dosimeters (CLODs) for low-dose measurements in computed tomography (CT). Monte Carlo (MC) simulations were conducted to evaluate the dose enhancement from the gold (Au) layers on the CLODs. The human eye and CLODs were modeled, and the X-ray tube voltages were defined as 80, 120, and 140 kVp. The thickness of the Au layer attached to a CLOD ranged from 100nm to 10μm. The thickness of the active layer ranged from 20 to 140μm. The dose ratio between the active layer of the Au-coated CLOD and a CLOD without a layer, i.e., the dose enhancement factor (DEF), was calculated. The DEFs of the first 20-μm thick active layer of the 5-μm thick Au-coated CLOD were 18.4, 19.7, 20.2 at 80, 120, and 140 kVp, respectively. The DEFs decreased as the thickness of the active layer increased. The DEFs of 100-nm to 5-μm thick Au layers increased from 1.7 to 5.4 for 120-kVp X-ray tube voltage when the thickness of the active layer was 140μm. The MC results presented a higher sensitivity of Au-coated CLODs (∼20-times higher than that of CLODs without a gold layer). Au-coated CLODs can be applied to an evaluation of very low doses (a few cGy) delivered to patients during CT imaging.

Characterization of CaSiO3:Ce crystals for α- and X-ray detection

CaSiO3 crystals doped with 0.5%, 1.0% and 2.0% Ce were developed using the floating zone method, and the scintillation and thermally-stimulated luminescence (TSL) properties were evaluated. Under X-ray irradiation, the emission peaks due to the 5d–4f transitions of Ce3+ appeared at 360 nm in all the samples. Under 241Am 5.5 MeV α-ray irradiation, a clear full-energy peak appeared in all the samples, and the light yield of the 2.0% Ce doped-sample was 1040 ph/5.5 MeV-α. As a TSL dosimeter, the samples were very sensitive to X-rays and showed a good linear response from 0.1 to 1000 mGy, which was equivalent to the measurable sensitivity of commercial dosimeters for personal dose monitoring.

Three newly developed BeO-based OSL dosimeters

This work presents the structural, morphological, luminescent and dosimetric characteristics of newly produced BeO based ceramic pellets, namely, BeO:Na5%,Ce0.01%,Er0.01%, BeO:Na5%,Ce0.005%,Tb0.05%, and BeO:Na5%,Ce0.01%,Dy0.01% by a simultaneous comparison with the commercially developed BeO Thermalox 995 chips. In this study, the BeO-based ceramics have been prepared using the co-precipitation synthesis method. Their phase formation and morphology have been confirmed by x-ray diffraction (XRD), scanning electron microscopy (SEM), and Energy Dispersive x-ray (EDS) analyses. To investigate the luminescence characteristics of the studied samples for dosimetry applications, the trap properties were identified using the TL and OSL emissions, step-annealing curve analyses, and experimental determination of temperature dependence. It was investigated that luminescence bands located between 300 and 400 nm (i.e., 3–4 eV) are dependent on the same luminescence mechanism in all radiation-induced luminescence effects used in dosimetry (RL, TL, and OSL). These newly developed BeO dosimeters with high OSL sensitivity and good reproducibility gave a linear response to β-radiation exposure from 0.5 to 100 Gy. The energy response of the samples was discussed. Negligible decay of stored OSL was determined as almost 7% after 3 months of storage. The application of BeO dosimeters for medical monitoring was discussed in comparison to the OSL evaluations from the Thermalox 995.

High optical-throughput spectroscopic singlet oxygen and photosensitizer luminescence dosimeter for monitoring of photodynamic therapy.

We report a high light-throughput spectroscopic dosimeter system that is able to noninvasively measure luminescence signals of singlet oxygen (1 O2 ) produced during photodynamic therapy (PDT) using a CW (continuous wave) light source. The system is based on a compact, fiber-coupled, high collection efficiency spectrometer (>50% transmittance) designed to maximize optical throughput but with sufficient spectral resolution (~7nm). This is adequate to detect 1 O2 phosphorescence in the presence of strong luminescence background in vivo. This system provides simultaneous acquisition of multiple spectral data points, allowing for more accurate determination of luminescence baseline via spectral fitting and thus the extraction of 1 O2 phosphorescence signal based solely on spectroscopic decomposition, without the need for time-gating. Simultaneous collection of photons at different wavelengths improves the quantum efficiency of the system when compared to sequential spectral measurements such as filter-wheel or tunable-filter based systems. A prototype system was tested during in vivo PDT tumor regression experiments using benzoporphyrin derivative (BPD) photosensitizer. It was found that the treatment efficacy (tumor growth inhibition rate) correlated more strongly with 1 O2 phosphorescence than with PS fluorescence. These results indicate that this high photon-collection efficiency spectrometer instrument may offer a viable option for real-time 1 O2 dosimetry during PDT treatment using CW light.

Assessment of eye doses to staff involved in interventional cardiology procedures in Kuwait.

In this study, which is the first of its kind in the gulf region, eye doses of interventional cardiologists and nurses were measured using active dosimeters for left and right eyes, in 60 percutaneous coronary interventions in three main hospitals in Kuwait. The dose given in terms of Hp(0.07) per procedure when ceiling suspended screens were used by main operators ranged from 18.5 to 30.3 µSv for the left eye and from 12.6 to 23.6 µSv for the right eye. Taking into account typical staff workload, the results show that the dose limit of 20 mSv/year to the eyes can be exceeded for interventional cardiologists in some situations, which demonstrates the need of using additional effective radiation protection tools, e.g. protective eye spectacles, in addition to the regular and proper use of ceiling suspended screens. With indications of increase in workload, the need for availability of a dedicated active dosimeter for the regular monitoring of eye doses is emphasized.

1,10-Bis(diphenylamino)-4,6-decadiyne as an active component of a radiochromic film dosimeter

Gamma-irradiation processes are very important tools for minimizing microbial load in dry food, inhibiting the proliferation of T-lymphocytes in blood, and for the sterilization of medical devices. To this end, a composite film dosimeter made of a radiation-sensitive monomer, 1,10-bis(diphenylamino)-4,6-decadiyne (DPD), embedded in poly(vinyl alcohol) was prepared using an automatic film applicator system. This polymeric film undergoes a color change from pale yellow to deep orange upon γ-irradiation due to topochemical polymerization of the DPD monomer. This color change is proportional to the amount of absorbed dose. With increasing absorbed doses, gradual disappearance of the νC≡C Raman band of the C≡C-C≡C chemical groups is observed, and new νC≡C and νC=C bands ascribed to the formation of a polydiacetylene with an enyne structure are detected. The irradiated films exhibited two absorption maxima at 470 and 502 nm as measured by UV-Vis spectrophotometry, and the intensities of these bands increased with increasing absorbed doses. Analysis of these films using a high-resolution flatbed scanner (2400 dpi) showed an increase in optical density with increasing absorbed doses up to 269.1 kGy. Stability studies revealed that the irradiated films underwent an increase in the color intensity by ∼3.1% over 50 days of storage. In addition, relative humidities in the range 0–75.3% had a limited impact on the dose response of the films, with a 4% change in this range. The uncertainty (2σ) on dose measurements using the scanner was 4.46%, demonstrating the effectiveness of this film dosimeter for radiation monitoring up to 296.1 kGy.

Development of LED based OSL dosimeters for personal monitoring

A subset of solid state materials have long been used as integrating dosimeters because they store energy deposited as a result of their interactions with ionizing radiation and then, when stimulated appropriately, release a proportionate amount of visible or near-visible light. During the 1960s, thermoluminescent dosimeters (TLDs), for which heat is used to extract the stored dosimetric signal, began to replace the photographic film as occupational dosimeters of record and for medical dosimetry. At the end of the twentieth century, a viable optically stimulated luminescent (OSL) material was developed which is now gaining in popularity as both an occupational and medical dosimeter. In this paper we give the designing and study of LED based OSL dosimeters for personal monitoring

TL Characteristics and Dosimetric Aspects of Mg-Doped ZnO

Dosimetry characterization and the evaluation of kinetics parameters of trapping states of Mg-doped ZnO phosphors synthesized by Sol-Gel technique. The thermoluminescence response of Mg-doped ZnO samples showed a linear response when exposed to X-ray radiation and the optimum annealing condition was 400oC/4h for the three concentrations. A broad-shaped TL glow curve with an upper bound of 270 °C, which shifts to lower temperatures with increasing dose, indicating that general order (GO) kinetics thermoluminescence processes are involved. We conclude that the ZnO doped Mg phosphors under study are promises to develop dosimeters for high radiation dose measurements. Kinetic parameters, such as activation energy (E), frequency factor (s), and order of kinematic order (b), were estimated by the Glow Curve Deconvolution (GCD) method. ZnO:Mg phosphor has a great potential as a dosimeter for monitoring in the fields of ionizing radiation.

Characterization of the Secondary Neutron Field Produced in a Thick Aluminum Shield by 1 GeV/u 56Fe Ions Using TLD-Based Ambient Dosimeters

The neutron ambient dose equivalent induced by galactic cosmic ray-like (1 GeV/u 56Fe) radiation stopped in a thick aluminum shield was measured at different angles with GSI neutron ball, the standard TLD (thermoluminescent dosimeters) based neutron dosimeter for area monitoring at the GSI facility. In order to measure reliably at large angles, a modified version of the GSI ball, including a set of three more sensitive TLD600H/700H cards, instead of one standard TLD600/700, cards was used. The modified GSI balls were calibrated in neutron reference fields of 241Am-Be(alpha,n) available at the Physikalisch-Technische Bundesanstalt (PTB). The neutron ambient dose equivalent was measured at 5 different angles (15, 40, 90, 115 and 130 degree) with respect to the beam direction and compared to the calculated detector response and ambient neutron dose equivalent results from FLUKA simulations. The dosimeter readings were corrected for signal contributions coming from secondary charged particles. An agreement within 15 % was found between the measured and calculated GSI ball response and an agreement within 30 % was found between experiments and calculated neutron dose equivalents.

Optical fiber dosimeter for real-time in-vivo dose monitoring during LDR brachytherapy.

An optical fiber sensor for monitoring low dose radiation is presented. The sensor, based on radiation sensitive scintillation material, terbium doped gadolinium oxysulphide (Gd2O2S:Tb), is embedded in a cavity of 700µm diameter within a 1mm plastic optical fiber. The sensor is compared with the treatment planning system for repeatability, angular dependency, distance and accumulated radiation activity. The sensor demonstrates a high sensitivity of 152 photon counts/Gy with a temporal resolution of 0.1 seconds, with the largest repeatability error of 4.1%, to 0.361mCi of Iodine-125 the radioactive source most commonly used in LDR brachytherapy for treating prostate cancer.