A personal thermoluminescence dosimeter using LiF:Mg,Cu,Na,Si detectors for photon fields.

A new personal thermoluminescence (TL) dosimeter for photon fields using LiF:Mg,Cu,Na,Si TL detector was developed by taking advantage of its dosimetric properties including energy dependencies. Solid pellet type LiF:Mg,Cu,Na,Si detector was developed and fabricated at Korea Atomic Energy Research Institute (KAERI) and has been studied on its dosimetric properties such as TL grow curve, dose response, energy response and reusability. Its dosimetric properties show the feasibility of application of LiF:Mg,Cu,Na,Si TL detector to personal dosimetry fields. A new dosimeter using LiF:Mg,Cu,Na,Si TL detector was designed and tested through irradiation experiments. This multi-element TL dosimeter allows the measurement of a personal dose equivalent Hp(d) in photon fields. Based on the experimental results of the proposed dosimeter, it was demonstrated that a personal TL dosimeter using sintered LiF:Mg,Cu,Na,Si TL detector is appropriate to estimate personal dose equivalent for wide range energy of photon fields.     

The effect of beam tube potential variation on gonad dose to patients during chest radiography investigated using high sensitivity LiF:Mg,Cu,P thermoluminescent dosemeters

Optimization of X-ray beam tube potential (kVp) in radiological examinations can minimize patient dose. This research aims to investigate the effect of tube potential variation on gonad doses to patients during posteroanterior (PA) chest radiography examinations. This study was carried out using a Toshiba general purpose X-ray unit and a Rando phantom. Dose measuring equipment included an ion chamber system, a dose-area product (DAP) meter and a thermoluminescent dosemeter (TLD) reader system with high sensitivity TLD pellets of LiF:Mg,Cu,P for low level gonad dose measurement. PA chest exposures of the phantom to produce a constant exit dose were made using a standard low tube potential (range 60-100 kVp) non-grid technique and a high tube potential (range 95-150 kVp) grid technique. Entrance surface doses (ESDs) and DAPs were also included in the measurements. Effective doses (EDs) were computed from ESD and DAP measurements using NRPB-SR262 and Xdose software. Results show that with the low tube potential technique both ovary dose and testes dose increase with increasing tube potential; statistically significant correlations of r = 0.994 (p = 0.0006) and r = 0.998 (p = 0.001), respectively, were found. For both organs, doses increase at a rate of approximately 2% per kVp. With the high tube potential technique there is insignificant correlation between gonad doses and tube potential. When comparing patient doses from typical exposures made at 70 kVp (low tube potential non-grid technique) with doses from exposures made at 120 kVp (high tube potential grid technique), the high tube potential technique delivers significantly higher values for ESD, and ovary, testes and effective doses by factors of 1.7, 5.2, 5.5 and 2.7, respectively.     

Investigation of dose reduction in neonatal radiography using specially designed phantoms and LiF:Mg,Cu,P TLDs

Many departments still do not use recommended radiographic parameters to X-ray neonates. Direct, accurate dose measurements of individual examinations may assist a department in justifying technique modifications that provide a substantial dose reduction without a significant loss of image quality. The aim of this study was to investigate dose reduction techniques for neonates in the intensive care unit. Alterations in beam energy (kVp and filtration) and collimation were investigated using specially designed phantoms mimicking a 700 g and 2000 g neonate, and ultrasensitive LiF:Mg,Cu,P thermoluminescence dosimeters (TLDs). Differences in entrance surface dose (ESD) and dose at depth (3 cm or 5 cm) were compared for two, overlapping fields centred individually on the chest and abdomen (Technique 1) and one large chest-abdomen field (Technique 2 or babygram). The large phantom was irradiated at 54 kVp, 60 kVp and 70 kVp without additional filtration and at 66 kVp and 70 kVp with a rare-earth hafnium filter. Focus-film distance (FFD) and mAs were adjusted to maintain optical density (OD) on each radiograph. The baseline dose at 54 kVp and 100 cm FFD was (46+/-2) micro Gy. Increasing the tube potential from 54 kVp to 70 kVp without additional filtration reduced the ESD by 27%. However, the addition of a 0.05 mm hafnium filter at 66 kVp further reduced the radiation dose by 13%, to produce an ESD of (28+/-2) micro Gy. All contrast details were observable at 66 kVp with hafnium filtration. Technique 1 may lead to an increase in effective dose due to field overlap, which diverges at depth, and increased scatter at the periphery of the fields.     

Comparison of the TL responses of two different preparations of LiF:Mg,Cu,P irradiated by photons of various energies.

The aim of this work is to present the results concerning the photon irradiation of a new phosphor, the LiF:Mg,Cu,P+PTFE, produced at the Instituto Nacional de Investigaciones Nucleares (ININ-Mexico). The photon irradiations were performed using X-rays of 16, 24, 34.5, 42, 100 and 145keV, and gamma rays from (137)Cs (662keV) and from (60)Co (1 252keV). The results obtained are normalized to the (60)Co response. The experimental data are then compared to those obtained using the commercial dosimeters TLD-100 and GR-200A.     

Towards in vivo TLD dosimetry in mammography

While phantoms are used for quality control assessment of the mammography unit, in vivo dose measurements are necessary to account for the variation in size and composition of the female breast. The use of thermoluminescent dosimeters (TLDs) in mammography has been limited due to TLD visibility. The aim of this current investigation was to access the suitability of a paper-thin LiF:Mg,Cu,P TLD (GR-200F) for in vivo dosimetric mammography measurements. The visibility of GR-200F has been directly compared with LiF:Mg,Cu,P TLDs (GR-200A) using a number of commercially available phantoms. The phantoms of thickness 2-5 cm were imaged over the range of tube potentials (24-28 kVp) used clinically. Both types of TLD were placed on the surface of the phantoms allowing assessment of visibility, entrance surface dose (ESD) and field homogeneity. In vivo assessment of ESD and visibility was also carried out on a volunteer undergoing a routine mammography examination. The positions of the GR-200F TLDs were not identified either on the image of the Leeds TOR(MAM) phantom or the patient mammograms. The average ESD for the Leeds phantom was 8.8 mGy, while the patient ESD was 13 mGy. It is now possible to perform in vivo measurements with the potential of increasing the accuracy of the doses measured for women that do not conform to a standard breast thickness or density.     

Further studies on higher temperature TL glow peaks of 7LiF:Mg,Ti

Thermoluminescence (TL) characteristics of the higher temperature peaks of LiF:Mg,Ti, which exhibit a unique property of high relative response to high LET radiation, were studied in view of some recent findings and discussions. By making separate readouts of dosimetric peaks (mainly peak 5) and higher temperature peaks (mainly peak 7), the precision in TL measurements, reusability and, fading were found comparable for the TL readouts in the two regions. However, the intensity of higher temperature peaks was found to be susceptible to the annealing treatments. In the standard annealing treatment of LiF:Mg,Ti, namely, 400 °C for 1 h followed by 100 °C for 2 h, the intensity of the higher temperature glow peaks was significantly affected when the second step of lower temperature annealing treatment at 100 °C for 2 h was not used. The dose response function f(D) of higher temperature peaks to gamma rays in the range from 30 to 150 mGy was found to be within about 10% (−4 and +9%) but above 200 mGy it increased sharply. The intricacies of dosimetry of mixed fields of low and high LET radiation are discussed.     

Alpha particle radiation detection with LiF:Mg,Cu,P TL detectors using the TSEE technique

LiF:Mg,Cu,P sintered pellets were tested in relation to their exoemissive properties, to verify the possibility of their use for alpha radiation detection. The main dosimetric characteristics as the main glow peak occurring at about 207°C when irradiated with ²⁴¹Am sources, a linear TSEE response as a function of irradiation time and flux emission, and its suitable reproducibility show their usefulness for alpha radiation detection.     

The glow curve shapes of some thermoluminescence materials for alpha and gamma radiations

The glow curve shapes and peak height ratios of the following thermoluminescent materials for alpha and gamma radiations have been investigated: LiF: Mg, Cu, P; LiF: Mg, Cu; LiF: Mg, Ti; LiF: Ti and CaF₂: Dy.     

Dose measurements using thermoluminescent dosimeters and DoseCal software at two paediatric hospitals in Rio de Janeiro.

A dosimetric survey in paediatric radiology is currently being carried out at the paediatric units of two large hospitals in Rio de Janiero city: IPPMG (Instituto de Pediatria e Puericultura Martag?o Gesteira, University Hospital of Federal University of Rio de Janeiro) and IFF (Instituto Fernandes Figueira, FIOCRUZ). Chest X-ray examination doses for AP, PA and LAT projections of paediatric patients have been obtained with thermoluminescent dosimeters (TLDs) and with use of a software package DoseCal. In IPPMG and IFF 100 patients have been evaluated with the use of the TLDs and another group of 100 patients with the DoseCal software. The aim of this work was to estimate the entrance skin dose (ESD) for frontal, back and lateral chest X-rays exposure of paediatric patients. For ESD evaluation, three different TL dosimeters have been used, namely LIF:Mg,Ti (TLD100), CaSO4:Dy and LiF:Mg,Cu,P (TLD100H). The age intervals considered were 0-1, 1-5, 5-10 and 10-15 years. The results obtained with all dosimeters are similar, and it is in good agreement with the DoseCal software, especially for AP and PA projections. However, some larger discrepancies are presented for the LAT projection.     

Investigation of dosimetric characteristics of the high sensitivity LiF:Mg,Cu,P Thermoluminescent Dosemeter and its applications in diagnostic radiology—a review

This study investigated the dosimetric properties of the high sensitivity TLD (Thermoluminescent Dosemeter) of LiF:Mg,Cu,P and its applications in diagnostic radiology. A reproducible readout and annealing regime for this high sensitivity TLD was developed in the initial part of this study with the newly installed automatic TLD Reader system. Basic dosimetric characteristics of this T.L. dosemeter were then investigated. This paved the foundation for subsequent selected novel application studies in diagnostic radiology. This study exploits the favourable dosimetric properties of these T.L. dosemeters in some selected novel dosimetric applications in diagnostic radiology with an anthropomorphic phantom. The applications studied in radiological procedures included: dose reduction in lumbar spine radiography utilizing the “anode heel effect”; gonad dose variation with kV_p in chest radiography; foetal dose comparison between computed tomography (CT) and computed radiography (CR) in X-ray pelvimetry; lens dose reduction with bismuth eye-shields in CT brain studies; foetal dose assessment of early pregnancy in common high risk radiological examinations. It is anticipated that the unique and favourable dosimetric performance of LiF:Mg,Cu,P T.L. phosphor will be exploited further in measurements of low level dose received by patients and staff in diagnostic radiological procedures such as paediatric X-ray examinations.     

Characterization of high-sensitivity metal oxide semiconductor field effect transistor dosimeters system and LiF:Mg,Cu,P thermoluminescence dosimeters for use in diagnostic radiology

Monitoring radiation exposure during diagnostic radiographic procedures has recently become an area of interest. In recent years, the LiF:Mg,Cu,P thermoluminescence dosimeter (TLD-100H) and the highly sensitive metal oxide semiconductor field effect transistor (MOSFET) dosimeter were introduced as good candidates for entrance skin dose measurements in diagnostic radiology. In the present study, the TLD-100H and the MOSFET dosimeters were evaluated for sensitivity, linearity, energy, angular dependence, and post-exposure response. Our results indicate that the TLD-100H dosimeter has excellent linearity within diagnostic energy ranges and its sensitivity variations were under 3% at tube potentials from 40 Vp to 125 kVp. Good linearity was also observed with the MOSFET dosimeter, but in low-dose regions the values are less reliable and were found to be a function of the tube potentials. Both dosimeters also presented predictable angular dependence in this study. Our findings suggest that the TLD-100H dosimeter is more appropriate for low-dose diagnostic procedures such as chest and skull projections. The MOSFET dosimeter system is valuable for entrance skin dose measurement with lumbar spine projections and certain fluoroscopic procedures.     

A system for electron therapy dosimetry surveys with thermoluminescence dosimeters

Radiation-therapy dosimetry surveys employing thermoluminescence dosimeters (TLDs) are now being considered for high-energy electron beams. Using a system of individually calibrated pressed LiF TLDs in a water and a polystyrene phantom, we established that the distortions of depth-dose distributions in non-conducting materials previously observed at high absorbed doses and high dose rates were not detectable in the present geometry at doses and dose rates as much as 40 times higher than those employed in radiation therapy. The system was then used to measure TLD response in water and in polystyrene in the nominal electron-energy range from 7 to 18 MeV. In the water phantom, the well-known trend for TLD response to decrease with increasing electron energy was observed. In the polystyrene phantom, TLD response was found to be independent of electron energy.     

Production of LiF:Ti thermoluminescence dosimeter material

Titanium (Ti) doped LiF:Ti thermoluminescent crystals were prepared and their dosimetric properties were studied. They showed different thermoluminescence sensitivies with increasing amounts of Ti dopings, reaching maximum for 400 ppm in LiF. In the glow curves of all samples, two peaks at 140°C and 210°C were observed. The stability of the traps connected with these peaks were studied for a period of one month. Dose-response and energy dependence properties of the stable 210°C peak were investigated between dose ranges of 200 mR and 200 R and 50 mR and 100 R for ¹³⁷Cs γ rays and x-rays respectively. Dose-response curves were found to be linear in these ranges. The energy dependence was 1.7% between 33 and 662 keV when the thermoluminescent responses were normalized to ¹³⁷Cs γ rays. It is suggested that LiF:Ti (400 ppm) may be used as a personnel dosimeter.     

Radiation dose quantities and risk in neonates in a special care baby unit

Radiographs are taken in the neonatal period most commonly to assist in the diagnosis and management of respiratory difficulties. Frequent accurate radiographic assessment is required and a knowledge of the radiation dose is necessary to justify such exposures. A survey of radiation doses to neonates from diagnostic radiography (chest and abdomen) has been carried out in the special care baby unit of the Royal Free Hospital. Entrance surface dose (ESD) was calculated from quality control measurements on the X-ray unit itself. Direct measurement of radiation doses was also performed using highly sensitive thermoluminescent dosemeters (TLDs) (LiF:Mg,Cu,P), calibrated and tested for consistency in sensitivity. ESD, as calculated from exposure parameters, was found to range from 28 microGy to 58 microGy, with a mean ESD per radiograph of 36+/-6 microGy averaged over 95 examinations. ESDs as derived from TLD crystals ranged from 18 microGy to 58 microGy for 30 radiographic examinations. The mean energy imparted, the mean whole body dose per radiograph and the mean effective dose were estimated to be 14+/-8 microJ, 10+/-4 microGy and 8+/-2 microSv, respectively. Assuming that neonates and fetuses are equally susceptible to carcinogenic effects of radiation, which involve an overestimation of risk, the radiation risk of childhood cancer from a single radiograph was estimated to be of the order (0.3-1.3) x 10(-6). Radiation doses compared favourably with the reference values of 80 microGy ESD published by the Commission of the European Communities in 1996, and 50 microGy published by the National Radiological Protection Board in 2000.     

Characterization of the glow-peak fading properties of six common thermoluminescent materials

The pre-irradiation and post-irradiation fading rates of the thermoluminescent glow peaks of six commonly used thermoluminescent dosimeters under controlled environmental conditions over approximately 30 d are examined. Glow peaks were fit to the first-order kinetics model using a computerized glow curve deconvolution program. Dosimeters studied were LiF:Mg,Ti, CaF₂:Dy, CaF₂:Tm, CaF₂:Mn, LiF:Mg,Cu,P, and CaSO₄:Dy. LiF:Mg,Ti and LiF:Mg,Cu,P experienced significant pre-irradiation fading. All types except CaF₂:Mn experienced post-irradiation fading. Ratios of glow-peak areas were fit to exponential decay functions when possible.     

Radiation exposure with the NOMAD portable X-ray system

OBJECTIVES: A new hand-held battery-operated portable X-ray system was tested for possible leakage radiation through the existing heavy metal compounds surrounding the X-ray tube, backscatter radiation through the lead-filled acrylic shield attached at the end of the exit tube and patient exposure. METHODS: Dose measurements were conducted using a DXTRR phantom and a water phantom. All measurements were recorded using calibrated thermoluminescent dosimetry (TLD), calibrated Unfors Model 583L dosemeter, and a calibrated Radcal MDH model 1015 dosemeter. The settings for all exposure were 60 kVp, 2.3 mA and 0.25 s using Kodak Insight (Class F) film. RESULTS: All backscatter measurements, in front of the shield, behind the shield, at the finger of the operator, the operator's chest, eyes and gonads were significantly below the maximum permissible radiation leakage as per the United States Food and Drug Administration regulations (100 mR h(-1)). Our measurements indicate that the exposure would be well within the occupational maximum permissible dose for an occupationally exposed person. Film dose was consistent with the manufacturer's recommendations. As a result of our measurements, the State of New York Bureau of Environmental Radiation Protection granted us a variance to use the NOMAD on a case-by-case basis. CONCLUSIONS: Our data have shown that the NOMAD presents risks that are no greater than with standard dental radiographic units to the patient or operator and the measured doses are well below recommended levels.     

Entrance dose measurement: a simple and reliable technique.

Verification of tumor dose for patients undergoing external beam radiotherapy is an important part of quality assurance programs in radiation oncology. Among the various methods available, entrance dose in vivo is one reliable method used to verify the tumor dose delivered to a patient. In this work, entrance dose measurements using LiF:Mg;Ti and LiF:Mg;Cu;P thermoluminescent dosimeters (TLDs) without buildup cap was carried out. The TLDs were calibrated at the surface of a water equivalent phantom against the maximum dose, using 6- and 10-MV photon and 9-MeV electron beams. The calibration geometry was such that the TLDs were placed on the surface of the "solid-water" phantom and a calibrated ionization chamber was positioned inside the phantom at calibration depth. The calibrated TLDs were then utilized to measure the entrance dose during the treatment of actual patients. Measurements were also carried out in the same phantom simultaneously to check the stability of the system. The dose measured in the phantom using the TLDs calibrated for entrance dose to 6-and 10-MV photon beams was found to be close to the dose determined by the treatment planning system (TPS) with discrepancies of not more than 4.1% (mean 1.3%). Consequently, the measured entrance dose during dose delivery to the actual patients with a prescribed geometry was found to be compatible with a maximum discrepancy of 5.7% (mean 2.2%) when comparison was made with the dose determined by the TPS. Likewise, the measured entrance dose for electron beams in the phantom and in actual patients using the calibrated TLDs were also found to be close, with maximum discrepancies of 3.2% (mean 2.0%) and 4.8% (mean 2.3%), respectively. Careful implementation of this technique provides vital information with an ability to confidently accept treatment algorithms derived by the TPS or to re-evaluate the parameters when necessary.     

Dosimetric study of thermoluminescent detectors in clinical photon beams using liquid water and PMMA phantoms

The purpose of this study was the dosimetric evaluation of thermoluminescent detectors of calcium sulphate doped with dysprosium (CaSO4:Dy) produced by IPEN compared to the TL response of lithium fluoride doped with magnesium and titanium (LiF:Mg,Ti) dosimeters and microdosimeters produced by Harshaw Chemical Company to clinical photon beams dosimetry (6 and 15 MV) using liquid water and PMMA phantoms.     

Dosimetric characterization of a newly designed encapsulated interstitial brachytherapy source of iodine-125-model LS-1 BrachySeed.

A newly designed encapsulated 125I source has been introduced (Model LS-1 BrachySeed manufactured by DRAXIMAGE Inc.) for interstitial brachytherapy. In this source 125I radionuclide is contained in two ceramic beads positioned at each end of a titanium capsule. The source contains a rod of Pt-Ir, which serves as a radiographic marker for source localization in the patient. Principle photon emissions are 27.4 and 31.0 keV X-rays and a 35.5 keV gamma-ray. The 22.2 and 25.5 keV silver X-rays produced by fluorescence of the silver dopant in the ceramic bead radioisotope carriers, are also emitted. In this work, the dosimetric characteristics of the 125I source were measured with micro LiF TLD chips and dosimetry parameters were characterized based upon the American Association of Physicists in Medicine, Task Group, No. 43 formalism. The corrected 1999 National Institute of Standards and Technology standard for low energy interstitial brachytherapy sources was used to specify the air kerma strength of the sources used in this study. The dose rate constant of the sources was determined to be 1.02+/-0.07 cGy h(-1) U(-1). The radial dose function was measured and was found to be similar to that of the silver-based model 6711 125I source. However, the anisotropy function of the Model LS-1 BrachySeed source is considerably better than that of model 6711 125I source, especially on the points along and close to the longitudinal axis of the source. The BrachySeed model LS-1 provides more isotropic angular dose distribution in tissue than model 6711 125I source. The anisotropy constant for the model LS-1 source was determined to be 1.006, which is considerably better than the value of 0.93 for the model 6711 source.     

3种无源固体探测器对低能X射线能量响应的研究

目的 研究3种无源固体探测器对低能X射线的能量响应,评估在乳腺X射线摄影检查中测量入射体表剂量和估算平均腺体剂量的可行性。方法 选用LiF(Mg,Ti)和LiF(Mg,Cu,P)热释光(TL)材料和A1₂O₃:C光致发光(OSL)材料的固体探测器,在Mo/Mo低能X射线机上,管电压25～40kV范围的10种线质分别曝光相同的空气比释动能。结果 给出管电压在25kV～40kV范围的10种辐射线质时TL和OSL能量响应,分别小于25％和11％。结论 A1₂O₃:C光释光探测器用于乳腺X射线摄影日常质量控制和入射体表剂量测量具有相当大的潜力。