Feasibility of using micro silica bead TLDs for in-Vivo dosimetry of CT-based HDR prostate brachytherapy: An experimental and simulation study.

PURPOSE: Feasibility of silica-based dosimeters for IVD of HDR prostate brachytherapy. MATERIAL AND METHODS: Plastic dosimeter holders and a water-fillable prostate phantom were built in-house. Interstitial prostate brachytherapy and Monte Carlo simulations were performed. The treatment planning, Monte-Carlo simulation, and dosimetry results were compared. RESULTS: The relative differences between TLD-TPS, TLD-MCNP, and TPS-MCNP were 0.2-6.9 %, 0.5-6.5 %, and 0.6-6.3 %, respectively. CONCLUSION: Micro-silica bead dosimeters can perform offline in situ quality assurance in HDR prostate brachytherapy.

Technologies for retrospective radiation dosimetry.

Radiation dosimetry is an important task for assessing the biological damages created in human being due to ionising radiation exposure. Ionising radiation being invisible and beyond the perception of human natural sensors, the dosimetry equipments/systems are the utmost requirement for its measurement. Retrospective measurement of radiation doses is a challenging task as conventional radiation dosemeters are not available at the exposure site. The material/s in close proximity of exposed individual or individuals' biological samples may be used as retrospective radiation sensor for dosimetry purpose. Environment materials such as sand, bricks, ceramics, sand stones, quartz, feldspar, glasses and electronic chips have been utilised using TL (Thermoluminescence) techniques for retrospective gamma dose (min 10 cGy) measurement. Electron Spin Resonance techniques have been employed to human biological samples such as tooth enamel, bones, nails, hair, etc. and reported for dosimetry for ~20 cGy min dose measurement. Some commercial glasses have been found sensitive enough to measure the minimum gamma doses of the order of 100 cGy using TL techniques. For internal retrospective dosimetry, the radioactivity contamination assessment in food items, water, other edible product and ambient air are the prerequisites. The radioactivity concentration vis-à-vis their consumption rate may help in controlling the internal contamination and estimation of dose absorption in human body. Defence Laboratory, Jodhpur has been working extensively on the dosimetry techniques for external dose measurement using environmental material and developed portable contamination monitoring systems for food and water radioactivity measurement in the range of 50 Bq kg-1 to 1000 kBq kg-1 in 60 s measurement time. The recent research and development in the methodologies, equipments and systems undertaken towards capacity building and self-reliance in retrospective radiation dosimetry is reported in this paper.

Assessment of peripheral dose as a function of distance and depth from cobalt-60 beam in water phantom using TLD-100.

BACKGROUND: Innovations in cancer treatment have contributed to the improved survival rate of cancer patients. The cancer survival rates have been growing and nearly two third of those survivors have been exposed to clinical radiation during their treatment. The study of long-term radiation effects, especially secondary cancer induction, has become increasingly important. An accurate assessment of out-of-field/peripheral dose (PDs) is necessary to estimate the risk of second cancer after radiotherapy and the damage to the organs at risk surrounding the planning target volume. This study was designed to measure the PDs as a function of dose, distances, and depths from Telecobalt-60 (Co-60) beam in water phantom using thermoluminescent dosimeter-100 (TLD-100). METHODS: The PDs were measured for Co-60 beam at specified depths of 0 cm (surface), 5 cm, 10 cm, and 15 cm outside the radiation beam at distances of 5, 10, and 13 cm away from the radiation field edge using TLD-100 (G1 cards) as detectors. These calibrated cards were placed on the acrylic disc in circular tracks. The radiation dose of 2000 mGy of Co-60 beam was applied inside 10 × 10 cm2 field size at constant source to surface distance (SSD) of 80 cm. RESULTS: The results showed maximum and minimum PDs at surface and 5 cm depth respectively at all distances from the radiation field edge. Dose distributions out of the field edge with respect to distance were isotropic. The decrease in PDs at 5 cm depth was due to dominant forward scattering of Co-60 gamma rays. The increase in PDs beyond 5 cm depth was due to increase in the irradiated volume, increase in penumbra, increase in source to axis distance (SAD), and increase in field size due to inverse square factor. CONCLUSION: It is concluded that the PDs depends upon depth and distance from the radiation field edge. All the measurements show PDs in the homogenous medium (water); therefore, it estimates absorbed dose to the organ at risk (OAR) adjacent to cancer tissues/planning target volume (PTV). It is suggested that PDs can be minimized by using the SAD technique, as this technique controls sources of scattered radiation like inverse square factor and effect of penumbra up-to some extent.

Graphite foils as potential skin and epithelium dosimeters at therapeutic photon energies.

This work builds upon a prior study, examining the dosimetric utility of pencil lead and thin graphitic sheets, focusing upon the measurement of skin doses within the mammographic regime. In recognizing the near soft-tissue equivalence of graphite and the earlier-observed favourable thermoluminescence yield of thin sheets of graphite, this has led to present study of 50 µm thick graphite for parameters typical of external beam fractionated radiotherapy and skin dose evaluations. The graphite layers were annealed and then stacked to form an assembly of 0.5 mm nominal thickness. Using a 6 MV photon beam and delivering doses from 2- to 60 Gy, irradiations were conducted, the assembly first forming a superficial layer to a solid water phantom and subsequently underlying a 1.5 cm bolus, seeking to circumvent the build-up to electronic equilibrium for skin treatments. Investigations were made of several dosimetric properties arising from the thermoluminescence yield of the 50 µm thick graphite slabs, in particular proportionality and sensitivity to dose. The results show excellent sensitivity within the dose range of interest, the thermoluminescence response varying with increasing depth through the stacked graphite layers, obtaining a coefficient of determination of 90%. Acknowledging there to be considerable challenge in accurately matching skin thickness with dose, the graphite sheets have nevertheless shown considerable promise as dosimeters of skin, sensitive in determination of dose from the surface of the graphite through to sub-dermal depth thicknesses.

Surface dose measurement and comparison between TLD and OSLD during modified re constructive mastectomy irradiation.

Radiotherapy (RT) is one of the major treatment modalities among surgery and chemotherapy for carcinoma breast. The surface dose study of modified reconstructive constructive Mastectomy (MRM) breast is important due to the heterogeneity in the body contour and the conventional treatment angle to save the lungs and heart from the radiation. These angular entries of radiation beam cause an unpredictable dose deposition on the body surface, which has to be monitored. Thermoluminescent dosimeter (TLD) or optically stimulated luminescent dosimeter (nano OSLD) are commonly preferable dosimeters for this purpose. The surface dose response of TLD and nano OSLD during MRM irradiation has been compared with the predicted dose from the treatment planning system (TPS). The study monitored 100 MRM patients by employing a total 500 dosimeters consisting of TLD (n = 250) and nano OSLD (n = 250), during irradiation from an Elekta Versa HD 6 MV Linear accelerator. The study observed a variance of 3.9% in the dose measurements for TLD and 3.2% for nano OSLD from the planned surface dose, with a median percentage dose of 44.02 for nano OSLD and 40.30 for TLD (p value 0.01). There was no discernible evidence of variation in dose measurements attributable to differences in field size or from patient to patient. Additionally, no variation was observed in dose measurements when comparing the placement of the dosimeter from central to off-centre positions. In comparison, a minor difference in dose measurements were noted between TLD and nano OSLD, The study's outcomes support the applicability of both TLD and nano OSLD as effective dosimeters during MRM breast irradiation for surface dose evaluation.

Thermoluminescence dosimetry (TLD) in a 3 T magnetic resonance imaging (MRI) environment: implications for personnel exposure monitoring.

Thermoluminescent dosimeters (TLDs) serve as compact and user-friendly tools for various applications, including personal radiation dosimetry and radiation therapy. This study explores the potential of utilizing TLD-100 personal dosimetry, conventionally applied in PET/CT (positron emission tomography/computed tomography) settings, in the PET/MRI (magnetic resonance imaging) environment. The integration of MRI into conventional radiotherapy and PET systems necessitates ionizing radiation dosimetry in the presence of static magnetic fields. In this study, TLD-100 dosimeters were exposed on the surface of a water-filled cylindrical phantom containing PET-radioisotope and positioned on the patient table of a 3 T PET/MRI, where the magnetic field strength is around 0.2 T, aiming to replicate real-world scenarios experienced by personnel in PET/MRI environments. Results indicate that the modified MR-safe TLD-100 personal dosimeters exhibit no significant impact from the static magnetic field of the 3 T PET/MRI, supporting their suitability for personal dosimetry in PET/MRI settings. This study addresses a notable gap in existing literature on the effect of MRI static magnetic field on TLDs.

Photoluminescence and thermoluminescence dosimetry properties of Ag/Y co-doped ZnO nanophosphor for radiation measurements.

This work explores the thermoluminescence (TL) and photoluminescence (PL) properties of Ag/Y co-doped zinc oxide (ZnO) nanophosphor. The proposed dosimeter was prepared by the coprecipitation method and sintered at temperatures from 400°C to 1000°C in an air atmosphere. Raman spectroscopy was studied to investigate the structural features of this composition. The new proposed dosimeter revealed two peaks at 150°C and 175°C with a small shoulder at high temperature (225°C). The PL spectrum showed strong green emissions between 500 to 550 nm. The Raman spectrum showed many bands related to the interaction between ZnO, silver (Ag), and yttrium oxide (Y2 O3 ). The rising sintering temperature enhanced the TL glow curve intensity. The Ag/Y co-doped ZnO nanophosphor showed an excellent linearity index within a dose from 1 to 4 Gy. The minimum detectable dose (MDD) of the Ag/Y co-doped ZnO nanopowder (pellets) equaled 0.518 mGy. The main TL properties were achieved in this work as follows: thermal fading (37% after 45 days at 1 and 4 Gy), optical fading (53% after 1 h and 68% after 6 h by exposure to sunlight), effective atomic number (27.6), and energy response (flat behavior from 0.1 to 1.3 MeV). Finally, the proposed material shows promising results nominated to be used for radiation measurements.

Synthesis and characterization of high-sensitivity Dy,Eu co-doped CaSO4 thermoluminescent phosphor using coprecipitation technique.

In this work, (99 - x)CaSO4 -Dy2 O3 -xEu2 O3 , (where x = 0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5) thermoluminescence phosphors were prepared using a coprecipitation method. The thermoluminescence (TL) dosimetry (TLD) characteristics such as TL sensitivity, dose-response, minimum detectable dose, thermal fading, and the effect of sunlight on the prepared phosphors were investigated. The obtained results indicated that the most sensitive phosphor was obtained at x = 0.05. Large thermal fading of 6% after 1 h and 26% after 24 h from irradiation followed by 71% after 1 month with no additional fading was observed within a time frame exceeding 2 months throughout the remaining duration of the investigation, which also spanned over 2 months. Despite the phosphor's high fading rate, the relative sensitivity of the prepared samples was ~90% compared with TLD-100. The marked effect of day sunlight was also determined. High dose-response within the low-dose range from 0.01 to 5 Gy was observed. The obtained results suggested that the synthesized phosphor is well suited for applications involving radiation biology and radiotherapy dosimetry.

Technical note: High-dose and ultra-high dose rate (UHDR) evaluation of Al2 O3 :C optically stimulated luminescent dosimeter nanoDots and powdered LiF:Mg,Ti thermoluminescent dosimeters for radiation therapy applications.

BACKGROUND: Dosimetry in ultra-high dose rate (UHDR) electron beamlines poses a significant challenge owing to the limited usability of standard dosimeters in high dose and high dose-per-pulse (DPP) applications. PURPOSE: In this study, Al2 O3 :C nanoDot optically stimulated luminescent dosimeters (OSLDs), single-use powder-based LiF:Mg,Ti thermoluminescent dosimeters (TLDs), and Gafchromic EBT3 film were evaluated at extended dose ranges (up to 40 Gy) in conventional dose rate (CONV) and UHDR beamlines to determine their usability for calibration and dose verification in the setting of FLASH radiation therapy. METHODS: OSLDs and TLDs were evaluated against established dose-rate-independent Gafchromic EBT3 film with regard to the potential influence of mean dose rate, instantaneous dose rate, and DPP on signal response. The dosimeters were irradiated at CONV or UHDR conditions on a 9-MeV electron beam. Under UHDR conditions, different settings of pulse repetition frequency (PRF), pulse width (PW), and pulse amplitude were used to characterize the individual dosimeters' response in order to isolate their potential dependencies on dose, dose rate, and DPP. RESULTS: The OSLDs, TLDs, and Gafchromic EBT3 film were found to be suitable at a dose range of up to 40 Gy without any indication of saturation in signal. The response of OSLDs and TLDs in UHDR conditions were found to be independent of mean dose rate (up to 1440 Gy/s), instantaneous dose rate (up to 2 MGy/s), and DPP (up to 7 Gy), with uncertainties on par with nominal values established in CONV beamlines (± 4%). In cross-comparing the response of OSLDs, TLDs and Gafchromic film at dose rates of 0.18-245 Gy/s, the coefficient of variation or relative standard deviation in the measured dose between the three dosimeters (inter-dosimeter comparison) was found to be within 2%. CONCLUSIONS: We demonstrated the dynamic range of OSLDs, TLDs, and Gafchromic film to be suitable up to 40 Gy, and we developed a protocol that can be used to accurately translate the measured signal in each respective dosimeter to dose. OSLDs and powdered TLDs were shown to be viable for dosimetric measurement in UHDR beamlines, providing dose measurements with accuracies on par with Gafchromic EBT3 film and their concurrent use demonstrating a means for redundant dosimetry in UHDR conditions.

Development of ring radiation dosemeters using 3D printing.

Extremity radiation monitoring is an important tool for the assessment of occupational exposures to staff at a variety of workplaces where ionising radiation is used. This work shows the feasibility of applying 3D printing for the development of customisable ring dosemeters. The rings were developed using two types of resin, hard and flexible and has the possibility of sterilisation using different techniques. The printed ring dosemeter was associated with BeO optically stimulated dosemeters. The energy and angular response were found within ±20% in the energy range from 24 to 662 keV and from 0° to 60° angle of incidence. This contributes to the reduction of measurement uncertainty when compared with currently used thermoluminescent detectors dosemeters. The new ring dosemeter showed a satisfactory response with respect to the performance criteria of the IEC 62387 Standard, in addition to providing improved ergonomics in relation to the commercial ring dosemeter.

Comparison of absorbed doses and organ doses measured with thermoluminescent dosimeters and Gafchromic film for cone beam computed tomography examination of the posterior mandibular region in a head phantom.

OBJECTIVES: We aimed to map the correlation between thermoluminescent dosimeters (TLDs) and Gafchromic film for measuring absorbed doses and to compare minimum, maximum, and mean absorbed doses over larger regions of interest and at various craniofacial organs and tissues during cone beam computed tomography (CBCT) exposure of the mandibular third molar region. STUDY DESIGN: We positioned TLDs at 75 measurement points in a head phantom. Gafchromic film was cut to the same shape as the 5 levels of the phantom and was placed on top of the TLDs. Both dosimetry methods thus included the surface of each level simultaneously. CBCT scans were made using a 5 × 5 cm field of view and a rotation angle of 200°. Measurements included absorbed dose distributions, doses at all 75 points, and minimum, maximum, and mean doses within organs and tissues. RESULTS: The correlation of point-dose measurements at all TLD sites with doses measured on film was strong (R2 = 0.9687), with greatest correlation at lower doses (<2 mGy). Large deviations between TLD and film measurements of minimum and maximum doses and absorbed doses to the organs occurred at all 5 levels. TLD positioning failed to cover several organ sites; for these, only absorbed dose measurements from the film were available. CONCLUSIONS: TLDs were unable to sample dose distributions and gradients accurately. The characteristics of Gafchromic LD-V1 film make it a favorable alternative in dental CBCT dosimetry.

Thermoluminescence dosimeter (TLD) studies of Ca10 K(PO4 )7 :Dy phosphor for applications in radiation dosimetry.

This study reports the thermoluminescence (TL) aspects of Ca10 K(PO4 )7 :Dy phosphor synthesized using a wet chemical method for the first time. The X-ray diffraction (XRD) results confirm the formation of the desired crystalline phase. Surface morphological studies reveal the formation of polyhedrons and agglomerations having an average diameter of 200 nm, while energy dispersive X-ray spectroscopy (EDS) data show the presence and composition of the elements in appropriate amounts. The effect of Dy doping concentration has been studied on the TL properties with exposure to gamma radiations from the Co-60 source. The best TL response has been observed for 5 mol% Dy doping concentration. The glow curve is simple and consists of a single peak at 130°C. The effect of the heating rate has been studied on the TL glow curve, and the heating rate of 5°C/s shows the best TL response. The various TL properties such as annealing conditions, dose-response, TL linearity, fading, and reusability of the prepared phosphor have been studied to check its suitability as a good TL dosimeter (TLD). TL characterization of the phosphor reports that the TL response is linear from 5- to 2000 Gy. The results show that this phosphor can be a good TLD for the dosimetry of gamma radiations from Co-60.

Optically stimulated luminescence detectors for dosimetry and LET measurements in light ion beams.

Objective.This work investigates the use of Al2O3:C and Al2O3:C,Mg optically stimulated luminescence (OSL) detectors to determine both the dose and the radiation quality in light ion beams. The radiation quality is here expressed through either the linear energy transfer (LET) or the closely related metricQeff, which depends on the particle's speed and effective charge. The derived LET andQeffvalues are applied to improve the dosimetry in light ion beams.Approach.OSL detectors were irradiated in mono-energetic1H-,4He-,12C-, and16O-ion beams. The OSL signal is associated with two emission bands that were separated using a pulsed stimulation technique and subjected to automatic corrections based on reference irradiations. Each emission band was investigated independently for dosimetry, and the ratio of the two emission intensities was parameterized as a function of fluence- and dose-averaged LET, as well asQeff. The determined radiation quality was subsequently applied to correct the dose for ionization quenching.Main results.For both materials, theQeffdeterminations in1H- and4He-ion beams are within 5 % of the Monte Carlo simulated values. Using the determined radiation quality metrics to correct the nonlinear (ionization quenched) detector response leads to doses within 2 % of the reference doses.Significance.Al2O3:C and Al2O3:C,Mg OSL detectors are applicable for dosimetry and radiation quality estimations in1H- and4He-ions. Only Al2O3:C,Mg shows promising results for dosimetry in12C-ions. Across both materials and the investigated ions, the estimatedQeffvalues were less sensitive to the ion types than the estimated LET values were. The reduced uncertainties suggest new possibilities for simultaneously estimating the physical and biological dose in particle therapy with OSL detectors.

TL glow curve and kinetic analysis of Na2SiO3:Pr3+ under beta radiation effect.

Ionizing radiation dosimetry with thermoluminescence (TL) materials based on silicon or glass can be interesting in its potential use in radiation monitoring as the solution to the constant looking of development of new radiation detectors. In this work, TL characteristics of sodium silicate exposed to beta radiation effects were studied. TL response beta irradiated exhibited a glow curve with two peaks centered at 398 K and 473 K. Samples showed linearity from 0.55 to 13.2 Gy. TL readings after 10 times showed a repeatability with an error of less than 1%. Remain information showed significant losses during the first 24 h, but its information was almost constant after 72 h of storage. The Tmax-Tstop method exhibited three peaks which were mathematically analyzed with a general order deconvolution finding kinetic orders close to the second order for the first peak, meanwhile the kinetic order for the second peak and third peak are close to second order. Finally, the VHR method showed anomalous TL glow curve behavior with an increasing intensity TL as the heating rate increased.

SYNTHESIS OF LIF:MG,TI NANOPARTICLES BY CO-PRECIPITATION METHOD AND EVALUATION OF INCREASING THE 5A/5 RATIO IN ALPHA AND GAMMA RADIATION.

The peak 5 in LiF: Mg, Ti includes sub-peaks 5a and 5b, which occur at the temperatures lower and higher than that of peak 5, respectively. Peak 5a in LiF:Mg,Ti occurs due to the localized recombination of trapping/luminescence center (TC/LC), in which the electron is released from the electron trap by obtaining energy from heat and recombines through the tunneling phenomenon with a hole located in the adjacent luminescence center at a distance of 3 nm. Concerning the standard TLD tablets, which are composed of micron-sized particles, the peak 5a either does not occur or appears with very low intensity, which is insignificant in terms of dosimetry. Thus, the present study focuses on synthesizing thermoluminescent nanoparticles by co-precipitation method in several stages by citing models based on the maintenance of linear behavior of thermoluminescence nanopowders up to high doses and its relationship with localized electron-hole recombination. In addition, by changing the concentration of ingredients, altering the temperature of the reaction medium and presence or absence of surfactant, nanoparticles with suitable geometric shapes were achieved. The synthesized nanopowders were irradiated with different doses of alpha and gamma, and after analyzing the glow curves, the increase in peak 5a/5 was reported as the main factor in nanodosimetry. Based on the results, the LiF: Mg, Ti thermoluminescence nanopowders can increase the 5a/5 ratio and can be used as a convenient, inexpensive and practical tool to estimate the amount of energy deposited by the beams in nanoscale.

3D in vivo dosimetry of HDR gynecological brachytherapy using micro silica bead TLDs.

PURPOSE: This study aimed to evaluate the feasibility of defining an in vivo dosimetry (IVD) protocol as a patient-specific quality assurance (PSQA) using the bead thermoluminescent dosimeters (TLDs) for point and 3D IVD during brachytherapy (BT) of gynecological (GYN) cancer using 60 Co high-dose-rate (HDR) source. METHODS: The 3D in vivo absorbed dose verification within the rectum and bladder as organs-at-risk was performed by bead TLDs for 30 GYN cancer patients. For rectal wall dosimetry, 80 TLDs were placed in axial arrangements around a rectal tube covered with a layer of gel. Ten beads were placed inside the Foley catheter to get the bladder-absorbed dose. Beads TLDs were localized and defined as control points in the treatment planning system (TPS) using CT images of the patients. Patients were planned and treated using the routine BT protocol. The experimentally obtained absorbed dose map of the rectal wall and the point dose of the bladder were compared to the TPSs predicted absorbed dose at these control points. RESULTS: Relative difference between TPS and TLDs results were -8.3% ± 19.5% and -7.2% ± 14.6% (1SD) for rectum- and bladder-absorbed dose, respectively. Gamma analysis was used to compare the calculated with the measured absorbed dose maps. Mean gamma passing rates of 84.1%, 90.8%, and 92.5% using the criteria of 3%/2 mm, 3%/3 mm, and 4%/2 mm were obtained, respectively. Eventually, a "considering level" of at least 85% as pass rate with 4%/2-mm criteria was recommended. CONCLUSIONS: A 3D IVD protocol employing bead TLDs was presented to measure absorbed doses delivered to the rectum and bladder during GYN HDR-BT as a reliable PSQA method. 3D rectal absorbed dose measurements were performed. Differences between experimentally measured and planned absorbed dose maps were presented in the form of a gamma index, which may be used as a warning for corrective action.

Low-cost commercial graphite-rich pencils subjected to electron irradiation for passive radiation dosimetry.

Various thicknesses of 2B grade polymer pencil lead graphite (PPLG) were used in the present study, which focussed on the alteration in crystalline lattice and the structural defect caused by the electron irradiation dosage ranging from 0.5 to 20 Gy delivered by an Elekta HD Linac. The fundamental trap parameters i.e. kinetics order (b), activation energy (E), and frequency factor (s) of the PPLG samples have been estimated using the initial rise and peak shape approaches by fitting the thermoluminescence (TL) glow peaks of the PPLG samples exposed to 20 Gy. The lifetime of the TL glow peak is also presented, which provides information on the stability of the TL signal at maximum temperatures. Raman, Photoluminescence (PL), and X-ray diffraction (XRD) spectra are being used to observe the structural changes that have occurred as a result of the radiation doses. These spectroscopies offer an understanding of the physical parameters that are related to the defects and taking part in the luminescence process. When all of the data are taken into account, it is anticipated that 0.3 mm PPLG is an effective material for dosimetry. The results of these lines of research are intended to educate the innovation of versatile graphite radiation dosimeters as a low-cost efficient system for radiation detection. The studied PPLG offers tissue equivalence as well as high spatial resolution, both are desirable criteria for a material to be used in the monitoring of ionising radiation or a variety of medical applications.

Calculation of the half life for the thermoluminescent signal of Beryllium oxide.

Half-life is one of the fundamental parameters to characterize the thermoluminescent (TL) response in ionizing radiation dosimetry. In general, there are two types of important half-lives to model the phenomenon of thermoluminescence (TL). The first type of half-life is the time required for the concentration of trapped charge carriers in a single trap to decrease to half its initial value; this type of half-life is generally denoted as τ1/2. Experimentally, the loss of charge carriers and the corresponding half-life τ1/2 are not usually measured directly, but rather the intensity of the TL signal is measured at time t after the start of the experiment. The second type of half-life is the time required for the intensity of the TL to decay to half its initial value. This second type of half-life it is denoted by t1/2. Results of calculating the t1/2 half-life of the glow peaks of gamma irradiated BeO are presented. Calculations were made using the expressions derived in previous papers. To make this, the kinetic parameters (order of kinetics, activation energy and frequency factor) were previously determined. Results obtained could be useful in practical situations encountered in medical physics dosimetry.

Impact of thyroid gland shielding on radiation doses in dental cone beam computed tomography with small and medium fields of view.

OBJECTIVE: The purpose of this study was to evaluate the impact of thyroid gland shielding on radiation doses in dental cone beam computed tomography (CBCT) with small and medium fields of view (FOVs). STUDY DESIGN: Six CBCT protocols were investigated by exposing an adult anthropomorphic male phantom head without and with thyroid shielding, using 4 small (4 × 5 cm) and 2 medium (10 × 6 cm) FOVs. Twenty metal oxide semiconductor field-effect transistor dosimeters were placed in the phantom head to measure absorbed doses and calculate equivalent doses at 11 sites. Effective doses were calculated based on the tissue weighting factors in International Commission on Radiological Protection Publication 103. The data were analyzed using the independent samples t test. RESULTS: Thyroid gland shielding led to significant equivalent dose reductions in many tissues for all protocols. Equivalent dose reductions to the thyroid were significant in all 6 protocols (P ≤ .037). Significant reduction depended on the FOV and ranged between 24.5% and 42.6% for the thyroid gland and 4.9% and 34.5% for other tissues and organs. Effective doses were significantly lower in all protocols (P ≤ .016). CONCLUSIONS: Thyroid gland shielding protects the thyroid gland and other organs and should be utilized with all CBCT examinations where feasible.

Evaluating environmental radiations of the tomotherapy facility by optimizing full factorial design of the TLD technique.

BACKGROUND: In the last 40 years, the number of deaths due to cancer has been the highest in TaiwanOBJECTIVE: To optimize the readout system of the thermoluminescent dosimeter (TLD)-100H, the radiation rates among the Tomotherapy (TOMO) facility of the Department of Radiology Oncology of Chung Shan Medical University Hospital (CSMUH) were calculated with a 32 full factorial design (FFD). METHODS: A ten-month survey of the facility was employed using the sensitive and accurate TLD method. The TLD system was optimized for maximum temperature, heat rate, and preheat temperature of Harshaw 3500 reader. Eight analyzed groups with different factors were tested. RESULTS: The TOMO facility had significantly different radiation rates. The farther away from the gantry head, environmental radiation rates. The half value layer (HVL) was also determined. These results were compared with published. No significant contributions of environmental gamma radiations were detected except in the treatment room. CONCLUSIONS: Those were far below the occupational doses recommended by ICRP 60.