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1.
Phys Med Biol ; 68(3)2023 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-36595255

RESUMO

Objective.The aim of this work was to develop and validate a method for remote dosimetric auditing that enables dose-volume histogram parameter comparisons of measured and planned dose in the patient CT volume.Approach. The method is derived by adapting and combining a remote electronic portal imaging (EPID) based auditing method (Virtual Epid based Standard Phantom Audit-VESPA) and a method to estimate 3D in-patient dose distributions from planar dosimetric measurements. The method was tested with a series of error-induced plans including monitor unit and multileaf collimator (MLC) positioning errors. A pilot audit study was conducted with eleven radiotherapy centres. IMRT plans from two clinical trials, a post-prostatectomy (RAVES trial) plan and a head and neck (HPV trial) plan were utilized. Clinically relevant DVH parameters for the planned dose and estimated measured dose were compared.Main results. The method was found to reproduce the induced dose errors within 0.5% and was sensitive to MLC positioning errors as small as 0.5 mm. For the RAVES plan audit all DVH results except one were within 3% and for the HPV plan audit all DVH results were within 3% except three with a maximum difference of 3.2%.Significance. The results from the audit method produce clinically meaningful DVH metrics for the audited plan and could enable an improved understanding of a centre's radiotherapy quality.


Assuntos
Infecções por Papillomavirus , Radioterapia de Intensidade Modulada , Masculino , Humanos , Dosagem Radioterapêutica , Radioterapia de Intensidade Modulada/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Radiometria
2.
Radiat Oncol ; 18(1): 9, 2023 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-36631832

RESUMO

PURPOSE: To investigate the geometric and dosimetric impacts of intra-fractional movement for patients with single or multiple brain metastasis treated using Varian Hyperarc™ mono-isocentric radiosurgery. METHODS: A total of 50 single or hypo-fractionated Hyperarc™ treatment courses (118 lesions) were included in the analysis. Intra-fractional translational and rotational movements were quantified according to the post-treatment cone-beam CT (CBCT). Geometric displacements of all targets were calculated individually based on the assessed head movement in each treatment fraction and their relationships with treatment time and target-to-isocenter distances were studied. For dosimetric analysis, only single-fraction treatments (56 lesions) were included. Re-planning was performed with 0, 1, and 2 mm planning target volume (PTV) margins. Doses were then re-calculated on rotated CT images with isocenter shifted which emulate the change in patient treatment position. Target coverage, target and normal brain doses before and after intra-fractional movement were compared. RESULTS: The mean 3D target displacements was 0.6 ± 0.3 (SD) mm. Target shifts for patients treated within 10 min were significantly smaller than those treated in longer sessions. No correlation was found between target shift and target-to-isocenter distance as the origin of head rotation was not located at the isocenter. Loss of target coverage and minimum Gross Tumor Volume (GTV) dose due to intra-fractional movement were apparent only when no margin was used, leading to an extra 23% of the targets violating the dose acceptance criteria, in contrast, the effects on normal brain V12Gy were negligible regardless of the margin used. The use of 1 mm PTV margin can compensate clinically significant geographical miss caused by intra-fractional movements while limiting V12Gy to within dose criteria for 88% of the cases. The plan acceptance rate (fulfillment of both target and normal brain dose criteria) after intra-fractional movement was also the highest with the 1 mm margin. CONCLUSION: Although intra-fractional movements during Hyperarc™ treatments were small, there were substantial dosimetric effects due to the sharp dose fall-off near target boundaries. These effects could be mitigated by using a 1 mm PTV margin and maintaining the effective treatment time to within 10 min.


Assuntos
Neoplasias Encefálicas , Radiocirurgia , Humanos , Radiocirurgia/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Neoplasias Encefálicas/diagnóstico por imagem , Neoplasias Encefálicas/radioterapia , Neoplasias Encefálicas/cirurgia , Radiometria , Movimento , Dosagem Radioterapêutica
3.
Phys Med Biol ; 68(2)2023 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-36595234

RESUMO

Objective. Numerical models are central in designing and testing novel medical devices and in studying how different anatomical changes may affect physiology. Despite the numerous adult models available, there are only a few whole-body pediatric numerical models with significant limitations. In addition, there is a limited representation of both male and female biological sexes in the available pediatric models despite the fact that sex significantly affects body development, especially in a highly dynamic population. As a result, we developed Athena, a realistic female whole-body pediatric numerical model with high-resolution and anatomical detail.Approach. We segmented different body tissues through Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) images of a healthy 3.5 year-old female child using 3D Slicer. We validated the high anatomical accuracy segmentation through two experienced sub-specialty-certified neuro-radiologists and the inter and intra-operator variability of the segmentation results comparing sex differences in organ metrics with physiologic values. Finally, we compared Athena with Martin, a similar male model, showing differences in anatomy, organ metrics, and MRI dosimetric exposure.Main results. We segmented 267 tissue compartments, which included 50 brain tissue labels. The tissue metrics of Athena displayed no deviation from the literature value of healthy children. We show the variability of brain metrics in the male and female models. Finally, we offer an example of computing Specific Absorption Rate and Joule heating in a toddler/preschooler at 7 T MRI.Significance. This study introduces a female realistic high-resolution numerical model using MRI and CT scans of a 3.5 year-old female child, the use of which includes but is not limited to radiofrequency safety studies for medical devices (e.g. an implantable medical device safety in MRI), neurostimulation studies, and radiation dosimetry studies. This model will be open source and available on the Athinoula A. Martinos Center for Biomedical Imaging website.


Assuntos
Radiometria , Tomografia Computadorizada por Raios X , Adulto , Humanos , Masculino , Criança , Feminino , Pré-Escolar , Radiometria/métodos , Próteses e Implantes , Cabeça , Encéfalo , Imageamento por Ressonância Magnética
4.
J Radiol Prot ; 43(1)2023 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-36595231

RESUMO

Technologies utilizing radiological materials across power generation, defence, industry, research and medicine have increased the global inventory of highly active and hazardous materials. Consequently, an amplified threat exists of illicitly obtained materials being used as part of hostile acts. The potential for intentional releases occurs alongside risks from natural disasters or facility accidents. In any such event, it is crucial to rapidly assess the release composition and extent of response and remediation activities. Therefore, the deployment of an effective, resilient and autonomous radiation monitoring network is pivotal both during and after an incident. Underpinning this assessment is a detailed understanding of the pre-event or background, radiation levels, the knowledge of which is also essential in assessing a population's dosimetric exposure to, and impact from anthropogenic and naturally occurring/varying sources of ionizing radiation. Presented here is a fully operational cloud-based spectroscopic radiation mapping platform comprising IoT modules compatible with cellular networks, without modification, in over 180 countries. Combined with locally roaming vehicles, a continuous multi-pass radiological characterization of an urban environment was performed. Such IoT devices are deployable as either individual sensors for specific localized temporal events or integrated over a greater time period (and area) to represent a larger static sensor. Over several months of continued operation, more than 1000 000 individual location-referenced gamma-ray spectra were collected and securely uploaded, in real-time, to an online cloud database and automatically characterized via a custom multi-step workflow. Fine-scale local variations in the radiological fingerprint of a 1 km × 1 km urban area were subsequently rendered in near-real-time to an interactive secure online graphical dashboard for temporal, spatial and spectral interrogation by the user. Considerations for the automated 'elastic' handling of ever-expanding volumes of input data have been carried out, facilitating propagation and expansion of the system's database without human input.


Assuntos
Monitoramento de Radiação , Radiometria , Humanos , Monitoramento de Radiação/métodos , Radiação Ionizante
5.
Neuroimage ; 267: 119850, 2023 02 15.
Artigo em Inglês | MEDLINE | ID: mdl-36603745

RESUMO

Transcranial Magnetic Stimulation (TMS) is a non-invasive brain stimulation technique that uses a coil to induce an electric field (E-field) in the brain and modulate its activity. Many applications of TMS call for the repeated execution of E-field solvers to determine the E-field induced in the brain for different coil placements. However, the usage of solvers for these applications remains impractical because each coil placement requires the solution of a large linear system of equations. We develop a fast E-field solver that enables the rapid evaluation of the E-field distribution for a brain region of interest (ROI) for a large number of coil placements, which is achieved in two stages. First, during the pre-processing stage, the mapping between coil placement and brain ROI E-field distribution is approximated from E-field results for a few coil placements. Specifically, we discretize the mapping into a matrix with each column having the ROI E-field samples for a fixed coil placement. This matrix is approximated from a few of its rows and columns using adaptive cross approximation (ACA). The accuracy, efficiency, and applicability of the new ACA approach are determined by comparing its E-field predictions with analytical and standard solvers in spherical and MRI-derived head models. During the second stage, the E-field distribution in the brain ROI from a specific coil placement is determined by the obtained rows and columns in milliseconds. For many applications, only the E-field distribution for a comparatively small ROI is required. For example, the solver can complete the pre-processing stage in approximately 4 hours and determine the ROI E-field in approximately 40 ms for a 100 mm diameter ROI with less than 2% error enabling its use for neuro-navigation and other applications. Highlight: We developed a fast solver for TMS computational E-field dosimetry, which can determine the ROI E-field in approximately 40 ms for a 100 mm diameter ROI with less than 2% error.


Assuntos
Encéfalo , Estimulação Magnética Transcraniana , Humanos , Estimulação Magnética Transcraniana/métodos , Encéfalo/fisiologia , Cabeça , Radiometria , Imageamento por Ressonância Magnética/métodos
6.
Anticancer Res ; 43(2): 581-589, 2023 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-36697058

RESUMO

BACKGROUND/AIM: The focus of this report is establishing an irradiation arrangement to realize an ultra-high dose-rate (uHDR; FLASH) of scanned carbon-ion irradiation possible with a compact commonly available medical synchrotron. MATERIALS AND METHODS: Following adjustments to the operation it became possible to extract ≥1.0×109 carbon ions at 208.3 MeV/u (86 mm in range) per 100 ms. The design takes the utmost care to prevent damage to monitors, particularly in the nozzle, achieved by the uHDR beam not passing through this part of the apparatus. Doses were adjusted by extraction times, using a function generator. After one scan by the carbon-ion beam it became possible to create a field within the extraction time. The Advanced Markus chamber (AMC) and Gafchromic film are then able to measure the absolute dose and field size at a plateau depth, with the operating voltage of the chamber at 400 V at the uHDR for the AMC. RESULTS: The beam scanning utilizing this uHDR irradiation could be confirmed at a dose of 6.5±0.08 Gy (±3% homogeneous) at this volume over at least 16×16 mm2 corresponding to a dose-rate of 92.3 Gy/s (±1.3%). The dose was ca. 0.7, 1.5, 2.9, and 5.4 Gy depending on dose-rate and field size, with the rate of killed cells increasing with the irradiation dose. CONCLUSION: The compact medical synchrotron achieved FLASH dose-rates of >40 Gy/s at different dose levels and in useful field sizes for research with the apparatus and arrangement developed here.


Assuntos
Radioterapia com Íons Pesados , Síncrotrons , Humanos , Carbono , Planejamento da Radioterapia Assistida por Computador , Dosagem Radioterapêutica , Radiometria
7.
Sensors (Basel) ; 23(2)2023 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-36679500

RESUMO

It has become increasingly important to monitor environment contamination by such chemicals as chemical warfare agents (CWAs) and industrial toxic chemicals (TICs), as well as radiation hazards around and inside collective protection facilities. This is especially important given the increased risk of terrorist or military attacks. The Military Institute of Chemistry and Radiometry (MICR) has constructed and developed the ALERT device for the effective monitoring of these threats. This device uses sensors that detect chemical and radiological contaminations in the air. The CWA detector is an ion mobility spectrometer, TICs are detected by electrochemical sensors, and radiation hazards are detected via Geiger-Muller tubes. The system was designed to protect the crew from contamination. When chemical or radioactive contamination is detected at the air inlet for the shelter, air filtration through a carbon filter is activated. At this time, the air test procedure at the filter outlet is started to test the condition of the filter on an ongoing basis. After detecting contamination at the filter outlet, the system turns off the air pumping and the service can start the procedure of replacing the damaged carbon filter. This paper presents the results of laboratory testing of the ALERT gas alarm detector, which showed high measurements for important parameters, including sensitivity, repeatability, accuracy, and speed.


Assuntos
Poluição do Ar , Substâncias para a Guerra Química , Monitoramento de Radiação , Substâncias para a Guerra Química/análise , Poluição Ambiental , Radiometria
8.
Sensors (Basel) ; 23(2)2023 Jan 12.
Artigo em Inglês | MEDLINE | ID: mdl-36679681

RESUMO

The interest in fiber Bragg gratings dosimeters for radiotherapy dosimetry lies in their (i) submillimeter size, (ii) multi-points dose measurements, and (iii) customizable spatial resolution. However, since the radiation measurement relies on the thermal expansion of the surrounding polymer coating, such sensors are strongly temperature dependent, which needs to be accounted for; otherwise, the errors on measurements can be higher than the measurements themselves. In this paper, we test and compare four techniques for temperature compensation: two types of dual grating techniques using different coatings, a pre-irradiation and post-irradiation temperature drift technique, which is used for calorimetry, and finally, we developed a real-time interpolated temperature gradient for the multi-points dosimetry technique. We show that, over these four tested techniques, the last one outperforms the others and allows for real-time temperature correction when an array of 13 fiber Bragg gratings spatially extending over the irradiation zone is used. For a 20 Gy irradiation, this technique reduces the measurement errors from 200% to about 10%, making it suitable for a radiotherapy dose range. Temperature correction for medical low-dose range dosimetry is a first in our field and is essential for clinical FBG dosimetry applications.


Assuntos
Dosímetros de Radiação , Radiometria , Temperatura , Radiometria/métodos , Doses de Radiação , Polímeros
9.
Sensors (Basel) ; 23(2)2023 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-36679758

RESUMO

The two photon absorption-transient current technique (TPA-TCT) was used to investigate a silicon strip detector with illumination from the top. Measurement and analysis techniques for the TPA-TCT of segmented devices are presented and discussed using a passive strip CMOS detector and a standard strip detector as an example. The influence of laser beam clipping and reflection is shown, and a method that allows to compensate these intensity-related effects for investigation of the electric field is introduced and successfully employed. Additionally, the mirror technique is introduced, which exploits reflection at a metallised back side to enable the measurement directly below a top metallisation while illuminating from the top.


Assuntos
Fótons , Radiometria , Radiometria/métodos , Método de Monte Carlo , Imagens de Fantasmas , Silício
10.
Sensors (Basel) ; 23(2)2023 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-36679777

RESUMO

A fully transportable laser heterodyne radiometer (LHR), involving a flexible polycrystalline mid-infrared (PIR) fiber-coupling system and operating around 8 µm, was characterized and optimized with the help of a calibrated high temperature blackbody source to simulate solar radiation. Compared to a mid-IR free-space sunlight coupling system, usually used in a current LHR, such a fiber-coupling system configuration makes the mid-infrared (MIR) LHR fully transportable. The noise sources, heterodyne signal, and SNR of the MIR LHR were analyzed, and the optimum operating local oscillator (LO) photocurrent was experimentally obtained. The spectroscopic performance of the MIR LHR was finally evaluated. This work demonstrated that the developed fully transportable MIR LHR could be used for ground-based atmospheric sounding measurements of multiple trace gases in the atmospheric column. In addition, it also has high potential for applications on spacecraft or on an airborne platform.


Assuntos
Lasers , Radiometria , Análise Espectral/métodos , Gases , Luz
11.
Sensors (Basel) ; 23(2)2023 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-36679803

RESUMO

Absolute measurement of radiant power in the X-ray region is essential for many applications in astrophysics, spectroscopy, and X-ray diagnostics. Comparison between different measuring methods is an effective way to check their reliability. In the present work, a comparison of X-ray radiant power absolute measurement between a free-air ionization chamber and a cryogenic electrical substitution radiometer was performed at Beijing Synchrotron Radiation Facility. The absolute radiant power obtained by these two methods were mutually compared via a transfer standard detector's spectral responsivity at a photon energy of 10 keV. The result of the comparison showed that the difference was 0.47%. A conclusion was reached that the free-air ionization chamber and the cryogenic electrical substitution radiometer agreed within the combined relative uncertainty of 3.35%.


Assuntos
Ionização do Ar , Radiometria , Raios X , Reprodutibilidade dos Testes , Radiometria/métodos , Radiografia
12.
Phys Med Biol ; 68(3)2023 Jan 20.
Artigo em Inglês | MEDLINE | ID: mdl-36595233

RESUMO

Objective. Regulators require that wireless power transfer (WPT) systems and other strong magnetic field sources are compliant with the basic restrictions (BR) defined as the limits of the fields induced in the human body, i.e. the induced electric field/current density/specific absorption rate limits. This can be achieved by demonstrating compliance with the reference levels (RL) defined in air without the human body, i.e. the incident electric/magnetic field limits. Local sources, such as WPT transmitters, generate non-uniform fields that can locally exceed the RL while the induced fields are still well below the BR. In these cases, robust compliance with BR can be demonstrated, generally requiring a large number of simulations. In this study, we proposed an efficient evaluation using a homogeneous phantom and applying a coverage factor to account for the local field enhancements caused by the dielectric contrasts of the highly inhomogeneous human tissues.Approach. The generally applicable coverage factors were derived from a statistical analysis of the field enhancements observed on four magnetic near-field sources placed at different separation distances (2-80 mm) and locations on the back of 12 anatomical models. The field enhancements were characterized by the ratios between the peak induced fields in the anatomical models and those in the homogeneous half-space phantom (ϵr= 55,σ= 0.75 S m-1,ρ= 1,000 kg m-3) at the same distance.Main results. The resulting 99th percentile coverage factors range from 1 and 9 depending on the dosimetric quantity.Significance. The use of these coverage factors reduces the compliance testing effort from hundreds of simulations to only one, and makes experimental testing feasible without the support of simulations. The study also demonstrates that running only a few use-case simulations with anatomical models may underestimate the exposure by more than 10 dB.


Assuntos
Campos Eletromagnéticos , Campos Magnéticos , Humanos , Radiometria , Eletricidade , Imagens de Fantasmas
13.
Radiat Oncol ; 18(1): 13, 2023 Jan 20.
Artigo em Inglês | MEDLINE | ID: mdl-36670476

RESUMO

BACKGROUND: The purpose of this work was to obtain the dosimetric parameters of the new GZP3 60Co high-dose-rate afterloading system launched by the Nuclear Power Institute of China, which is comprised of two different 60Co sources. METHODS: The Monte Carlo software Geant4 and EGSnrc were employed to derive accurate calculations of the dosimetric parameters of the new GZP3 60Co brachytherapy source in the range of 0-10 cm, following the formalism proposed by American Association of Physicists in Medicine reports TG43 and TG43U1. Results of the two Monte Carlo codes were compared to verify the accuracy of the data. The source was located in the center of a 30-cm-radius theoretical sphere water phantom. RESULTS: For channels 1 and 2 of the new GZP3 60Co afterloading system, the results of the dose-rate constant (Λ) were 1.115 cGy h-1 U-1 and 1.112 cGy h-1 U-1, and for channel 3 they were 1.116 cGy h-1 U-1 and 1.113 cGy h-1 U-1 according to the Geant4 and EGSnrc, respectively. The radial dose function in the range of 0.25-10.0 cm in a longitudinal direction was calculated, and the fitting formulas for the function were obtained. The polynomial function for the radial dose function and the anisotropy function (1D and 2D) with a [Formula: see text] of 0°-175° and an r of 0.5-10.0 cm were obtained. The curves of the radial function and the anisotropy function fitted well compared with the two Monte Carlo software. CONCLUSION: These dosimetric data sets can be used as input data for TPS calculations and quality control for the new GZP3 60Co afterloading system.


Assuntos
Braquiterapia , Radiometria , Humanos , Dosagem Radioterapêutica , Radiometria/métodos , Software , Radioisótopos de Cobalto , Método de Monte Carlo , Braquiterapia/métodos , Anisotropia
14.
Zhonghua Yi Xue Za Zhi ; 103(3): 199-204, 2023 Jan 17.
Artigo em Chinês | MEDLINE | ID: mdl-36649991

RESUMO

Objective: According to the formula provided by the TG43 report [AAPM TG43 (2004)] proposed by the American Association of Physicists in Medicine (AAPM) in 2004, we calculated the dose distribution around the radioactive iodine-125 particles, and verified the calculation accuracy of the radioactive iodine-125 particles treatment planning system. Methods: AAPM TG43 (2004) report provides two calculation methods when calculating the dose around a single radioactive source. The calculation method that does not consider the geometric structure of the radioactive source is called point source calculation method, and the calculation method that considers the geometric structure of the radioactive source is called line source calculation method. Assuming a single Amersham 6711 radioactive iodine-125 particle with an activity of 100 U, the following point doses were calculated according to the two calculation methods provided by AAPM TG43 (2004) report, at 0°, 90° directions, distances 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 and 6 cm; In the direction of 45°, the doses at 0.71, 1.41, 2.12, 2.83, 3.54, 4.24, 4.95, 5.66, 6.36, 7.07, 7.78 and 8.49 cm. On the clinically used brachytherapy planning system variseeds 8.0, the above two calculation methods are used to calculate the corresponding activity and the dose around the corresponding type of radioactive iodine-125 particles, and the function of capturing points to templates built in the planning system is used to accurately find the above corresponding point position, using a single measurement of the above corresponding point dose; and comparation of the results were performed to see if there is a statistical difference. Results: The AAPM TG43 report uses point source calculation method to calculate the dose of single Amersham 6711 radioactive iodine-125 particles with activity of 100 U at 0° and 90° directions. The points with the same distance and the same dose are 8 082.18, 1 870.08, 756.58, 381.47, 217.11, 131.91, 86.55, 58.32, 39.97, 27.42, 19.74, 14.13 Gy, respectively, at 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 and 6 cm away from them. In the 45° direction, the doses at the distances of 0.71, 1.41, 2.12, 2.83, 3.54, 4.24, 4.95, 5.66, 6.36, 7.07, 7.78 and 8.49 cm are 3 957.37, 865.83, 329.99, 155.69, 84.10, 48.50, 28.49, 17.80, 11.37, 7.38, 4.98 and 3.39 Gy, respectively; For line source calculation method, radioactive particles are at the same distance as above. The doses at each point in the direction of 0° are 3 128.71, 755.44, 330.30, 180.53, 107.74, 68.56, 46.40, 32.22, 22.70, 16.00, 11.51, 8.24 Gy, respectively. The doses at each point in the direction of 90° are 8 306.46, 1 981.01, 802.74, 405.38, 230.60, 140.03, 91.83, 61.84, 42.36, 29.05, 20.91, 14.97 Gy; In the 45° direction, the dose at the corresponding distance as above is 4 020.78, 877.43, 333.49, 156.93, 84.69, 48.81, 28.65, 17.89, 11.42, 7.41, 4.99 and 3.40 Gy, respectively. The maximum dose difference (0.3%) between the two methods is 7.78 cm in the 45° direction, the maximum difference (-0.3%) between the two methods is 8.49 cm in the 45° direction, and the value of other sampling points is less than 0.3%. The closer the Amersham 6711 iodine-125 particles are to the source in the directions of 0°, 45°, and 90°, the faster the dose will drop, and the dose will drop gradually as the distance increases. Conclusion: The brachytherapy planning system variseeds 8.0 and the AAPM TG43 report calculate a maximum dose difference of 0.3%, which can accurately calculate the dose distribution around radioactive iodine-125 seeds, and provide a reliable tool for the clinical implementation of radioactive iodine-125 particles implantation for tumor treatment.


Assuntos
Braquiterapia , Neoplasias da Glândula Tireoide , Humanos , Radioisótopos do Iodo , Dosagem Radioterapêutica , Método de Monte Carlo , Planejamento da Radioterapia Assistida por Computador/métodos , Radiometria/métodos
15.
Sensors (Basel) ; 23(2)2023 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-36679808

RESUMO

The production of thermoluminescence (TL) dosimeters fabricated from B2O3-CaF2-Al2O3-SiO2 doped with Cu and Pr for use in diagnostic radiology is the main goal of this research. The TL samples were synthesized via the melt-quench technique processed by melting the mixture at 1200 °C for 1 h, and, after cooling, the sample thus created was divided into two samples and retreated by heating for 2 h (referred to as TLV30) and for 15 h (referred to as TLV17). SEM and EDS analyses were performed on the TL samples to confirm the preparation process and to investigate the effects of irradiation dosimetry on the TL samples. Furthermore, the TL samples were irradiated with γ-rays using a 450 Ci 137Cs irradiator and variable X-ray beams (5-70 mGy). Two important diagnostic radiology applications were considered: CT (6-24 mGy) and mammography (2.72-10.8 mGy). Important dosimetric properties, such as the glow curves, reproducibility, dose-response linearity, energy dependence, minimum dose detectability and fading, were investigated for the synthetized samples (TLV17 and TLV30), the results of which were compared with the Harshaw TLD-100. The TLV17 dosimeter showed higher sensitivity than TLV30 in all applied irradiation procedures. The dose-response linearity coefficients of determination R2 for TLV17 were higher than TLD-100 and TLV30 in some applications and were almost equal in others. The reproducibility results of TLV17, TLV30 and TLD-100 were less than 5%, which is acceptable. On the other hand, the results of the fading investigations showed that, in general, TLV17 showed less fading than TLV30. Both samples showed a significant decrease in this regard after the first day, and then the signal variation became essentially stable though with a slight decrease until the eighth day. Therefore, it is recommended to read the TL dosimeters after 24 h, as with TLD-100. The SEM images confirmed the existence of crystallization, whilst the EDS spectra confirmed the presence of the elements used for preparation. Furthermore, we noticed that TLV17 had grown dense crystals that were larger in size compared to those of TLV30, which explains the higher sensitivity in TLV17. Overall, despite the fading, TLV17 showed greater radiation sensitivity and dose-response linearity compared with TLD-100. The synthetized TL samples showed their suitability for use as dosimeters in diagnostic radiology radiation dosimetry.


Assuntos
Radiologia , Silício , Dosímetros de Radiação , Alumínio , Cálcio , Temperatura Alta , Dióxido de Silício , Reprodutibilidade dos Testes , Boratos , Dosimetria Termoluminescente , Radiometria
16.
Biomed Phys Eng Express ; 9(2)2023 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-36689763

RESUMO

Purpose.To investigate the response of the CC13 ionization chamber under non-reference photon beam conditions, focusing on penumbra and build-up regions of static fields and on dynamic intensity-modulated beams.Methods. Measurements were performed in 6 MV 100 × 100, 20 × 100, and 20 × 20 mm2static fields. Monte Carlo calculations were performed for the static fields and for 6 and 15 MV dynamic beam sequences using a Varian multi-leaf collimator. The chamber was modelled using EGSnrc egs_chamber software. Conversion factors were calculated by relating the absorbed dose to air in the chamber air cavity to the absorbed dose to water. Correction and point-dose correction factors were calculated to quantify the conversion factor variations.Results. The correction factors for positions on the beam central axis and at the penumbra centre were 0.98-1.02 for all static fields and depths investigated. The largest corrections were obtained for chamber positions beyond penumbra centre in the off-axis direction. Point-dose correction factors were 0.54-0.71 at 100 mm depth and their magnitude increased with decreasing field size and measurement depth. Factors of 0.99-1.03 were obtained inside and near the integrated penumbra of the dynamic field at 100 mm depth, and of 0.92-0.94 beyond the integrated penumbra centre. The variations in the ionization chamber response across the integrated dynamic penumbra qualitatively followed the behaviour across penumbra of static fields.Conclusions. Without corrections, the CC13 chamber was of limited usefulness for profile measurements in 20-mm-wide fields. However, measurements in dynamic small irregular beam openings resembling the conditions of pre-treatment patient quality assurance were feasible. Uncorrected ionization chamber response could be applied for dose verification at 100 mm depth inside and close to large gradients of dynamically accumulating high- and low-dose regions assuming 3% tolerance between measured and calculated doses.


Assuntos
Radiometria , Software , Humanos , Radiometria/métodos , Método de Monte Carlo , Água
17.
Asian Pac J Cancer Prev ; 24(1): 141-147, 2023 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-36708562

RESUMO

OBJECTIVE: A study on dosimetric characteristics of silicon elastomer-based bolus was carried out using a Linear accelerator (Varian - Unique Performance). The study is performed to know if the silicone elastomer based bolus can be used in the radiotherapy. A bolus is a tissue equivalent material used to provide uniform dose to the uneven surface contours. It is exposed during the radiation therapy and also provides maximum dose (dmax) to treat surface tumors in case of high energy photons like megavoltage therapy photons. It is used in the case of external beam radiation therapy. METHODS: In this study, the bolus was fabricated using PDMS substrate with a curing agent by the ratio of 10:1. The bolus was fabricated in two thicknesses 0.5cm and 1cm. The dosimetric characteristics like transmission factor, mass attenuation coefficient, durability, homogeneity, density test of the fabricated bolus were studied. RESULTS: The dosimetric characteristics of the silicone elastomer based bolus were studied over a period of one month by exposing it in a 6MV photon. The result of the study shows that the silicone elastomer based bolus fabricated, satisfies the dosimetric characteristics needed for a tissue equivalent bolus to be used in the radiation therapy. CONCLUSIONS: The fabricated bolus could increase the percentage surface dose, reduce skin-sparing effect, and protect OAR. The aim of this is to provide an adjustable, transparent, and easily fabricated, less expensive, nontoxic bolus which can be used in the radiotherapy.


Assuntos
Elastômeros , Neoplasias , Humanos , Elastômeros de Silicone , Radiometria , Fótons/uso terapêutico , Neoplasias/radioterapia , Planejamento da Radioterapia Assistida por Computador , Dosagem Radioterapêutica , Imagens de Fantasmas , Radioterapia
18.
Health Phys ; 124(2): 125-128, 2023 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-36625836

RESUMO

ABSTRACT: In addition to a review of theoretical analyses, this work presents an empirical study of nasal swab data from the Los Alamos National Laboratory (LANL) database correlated with intake obtained from plutonium internal dosimetry calculations. As a result of this work, several "intake-versus-nasal-swab" models were derived. We advocate quantitative use of nasal swab measurements in dose assessment calculations and discuss ways that this can be done. The best description of the LANL plutonium internal dose database is arguably intake = A + Bx, where A = 2.7 Bq, B = 3.8, and x = summed nasal swab activity. The geometric standard deviation was found to be 8.2. This relationship, obtained using plutonium data, should apply also for other radionuclides.


Assuntos
Plutônio , Plutônio/análise , Radiometria , Radioisótopos
20.
Sensors (Basel) ; 23(1)2023 Jan 03.
Artigo em Inglês | MEDLINE | ID: mdl-36617110

RESUMO

In 2011, the International Commission on Radiological Protection (ICRP) recommended a significant reduction in the lens-equivalent radiation dose limit, thus from an average of 150 to 20 mSv/year over 5 years. In recent years, the occupational dose has been rising with the increased sophistication of interventional radiology (IVR); management of IVR staff radiation doses has become more important, making real-time radiation monitoring of such staff desirable. Recently, the i3 real-time occupational exposure monitoring system (based on RaySafeTM) has replaced the conventional i2 system. Here, we compared the i2 and i3 systems in terms of sensitivity (batch uniformity), tube-voltage dependency, dose linearity, dose-rate dependency, and angle dependency. The sensitivity difference (batch uniformity) was approximately 5%, and the tube-voltage dependency was <±20% between 50 and 110 kV. Dose linearity was good (R2 = 1.00); a slight dose-rate dependency (~20%) was evident at very high dose rates (250 mGy/h). The i3 dosimeter showed better performance for the lower radiation detection limit compared with the i2 system. The horizontal and vertical angle dependencies of i3 were superior to those of i2. Thus, i3 sensitivity was higher over a wider angle range compared with i2, aiding the measurement of scattered radiation. Unlike the i2 sensor, the influence of backscattered radiation (i.e., radiation from an angle of 180°) was negligible. Therefore, the i3 system may be more appropriate in areas affected by backscatter. In the future, i3 will facilitate real-time dosimetry and dose management during IVR and other applications.


Assuntos
Proteção Radiológica , Radiologia Intervencionista , Humanos , Doses de Radiação , Dosímetros de Radiação , Radiometria
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