The Effects of Breasts Shielding on Dose Reduction in CT Examinations (original) (raw)
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Characterization of a lead breast shielding for dose reduction in computed tomography
Radiologia brasileira
Several studies have been published regarding the use of bismuth shielding to protect the breast in computed tomography (CT) scans and, up to the writing of this article, only one publication about barium shielding was found. The present study was aimed at characterizing, for the first time, a lead breast shielding. The percentage dose reduction and the influence of the shielding on quantitative imaging parameters were evaluated. Dose measurements were made on a CT equipment with the aid of specific phantoms and radiation detectors. A processing software assisted in the qualitative analysis evaluating variations in average CT number and noise on images. The authors observed a reduction in entrance dose by 30% and in CTDIvol by 17%. In all measurements, in agreement with studies in the literature, the utilization of cotton fiber as spacer object reduced significantly the presence of artifacts on the images. All the measurements demonstrated increase in the average CT number and noise...
Journal of Applied Science and Environmental Management , 2019
Evaluation of radiation protective devices in radiology departments is one of the practices that ensure radiation protection and staff and patients safety in hospitals. A research work to evaluate 1.5mm lead shield used for radiological protection was carried out in Radiological Unit of Sharda Hospital, of Sharda University, India, using 300mA fixed x-ray machine room. The evaluation was done in the x-ray energy (kVp) range between 52-81 and by using calculative procedure and by direct measurement of the radiation dose rates. The two results were compared. The results shows that, in the absence of the shield, only 11.82% of the radiation exposure was attenuated by the air space before reaching the radiographer's stand, while in the presence of the shield, 96.50% was attenuated, whereas, for the measured result only 10.17% was attenuated in the absence of the shield and 89.83% was attenuated in the presence of the shield before reaching the radiographer's stand. The unit of radiation exposure was converted to that of equivalent dose and that of effective dose in order to assess the radiographer's safety level behind the shield. It was found that, the equivalent/effective dose is as low as to be accepted according to the policy of ALARA (As Low As Reasonably Achievable), and within the NCRP recommended limit. This guaranteed the effectiveness of the lead shield of 1.5mm thickness in the x-ray energy range used in this study.
Biomedical Journal, 2019
Background: To quantify image quality and radiation doses in regions adjacent to and distant from bismuth shields in computed tomography (CT). Methods: An American College of Radiology accreditation phantom with four solid rods embedded in a water-like background was scanned to verify CT number (CTN) accuracy when using bismuth shields. CTNs, image noise, and contrast-to-noise ratios (CNRs) were determined in the phantom at 80e140 kVp. Image quality was investigated on image portions in the zones adjacent (A zone) to and distant (D zone) from a bismuth shield. Surface radiation doses were measured using thermoluminescent dosimeters. Streak artefacts were graded on a 3-point-scale. Results: Changes in CTN caused by a bismuth shield resulted in changes in X-ray spectra. CTN changes were more apparent in the A zone than in the D zone, particularly for a low tube voltage. The degrees of CTN changes and image noise were proportional to the thickness of the bismuth shields. A 1-ply bismuth shield reduced surface radiation doses by 7.2%e15.5%. The overall CNRs were slightly degraded, and streak artefacts were acceptable. Conclusions: Using a bismuth shield could result in significant CTN changes and perceivable artefacts, particularly for a superficial organ close to the shield, and is not recommended for quantification CT examinations or follow-up CT examinations.
Medical Physics, 2011
The purpose of this work was to evaluate dose performance and image quality in thoracic CT using three techniques to reduce dose to the breast: bismuth shielding, organ-based tube current modulation (TCM) and global tube current reduction. Methods: Semi-anthropomorphic thorax phantoms of four different sizes (15, 30, 35, and 40 cm lateral width) were used for dose measurement and image quality assessment. Four scans were performed on each phantom using 100 or 120 kV with a clinical CT scanner: (1) reference scan; (2) scan with bismuth breast shield of an appropriate thickness; (3) scan with organ-based TCM; and (4) scan with a global reduction in tube current chosen to match the dose reduction from bismuth shielding. Dose to the breast was measured with an ion chamber on the surface of the phantom. Image quality was evaluated by measuring the mean and standard deviation of CT numbers within the lung and heart regions. Results: Compared to the reference scan, dose to the breast region was decreased by about 21% for the 15-cm phantom with a pediatric (2-ply) shield and by about 37% for the 30, 35, and 40-cm phantoms with adult (4-ply) shields. Organ-based TCM decreased the dose by 12% for the 15-cm phantom, and 34-39% for the 30, 35, and 40-cm phantoms. Global lowering of the tube current reduced breast dose by 23% for the 15-cm phantom and 39% for the 30, 35, and 40-cm phantoms. In phantoms of all four sizes, image noise was increased in both the lung and heart regions with bismuth shielding. No significant increase in noise was observed with organ-based TCM. Decreasing tube current globally led to similar noise increases as bismuth shielding. Streak and beam hardening artifacts, and a resulting artifactual increase in CT numbers, were observed for scans with bismuth shields, but not for organ-based TCM or global tube current reduction. Conclusions: Organ-based TCM produces dose reduction to the breast similar to that achieved with bismuth shielding for both pediatric and adult phantoms. However, organ-based TCM does not affect image noise or CT number accuracy, both of which are adversely affected by bismuth shielding. Alternatively, globally decreasing the tube current can produce the same dose reduction to the breast as bismuth shielding, with a similar noise increase, yet without the streak artifacts and CT number errors caused by the bismuth shields. Moreover, globally decreasing the tube current reduces the dose to all tissues scanned, not simply to the breast. V
Real-time estimation of dose reduction for pediatric CT using bismuth shielding
Radiation Measurements, 2011
The purpose of this study is to estimate the dose reduction of bismuth shielding for pediatric CT using a real-time CT dose probe. Routine CT examinations of head, chest and abdomen were performed on a 10-year pediatric anthropomorphic phantom, with and without bismuth shield. A solid-state dosimeter was used to obtain real-time dose measurements and to estimate the dose reduction. The maximum dose reduction of eyes using bismuth shield for in-plane CT scanning can achieve 56% during spiral head scanning interval. The average dose reduction is around 25% for in-plane CT scanning, and reaches 62% combining the technique of automatic tube current modulation. The solid-state probe can provide fast and convenient measurements for dose estimation of superficial organs. It is suggested to use Bismuth shielding in routine CT examinations to protect the radiosensitive tissues.
Shielding Calculation for for Nuclear Medicine Services
Nuclear medicine is a medical specialization that uses radioactive materials injected into the body to diagnose and treat human diseases. The use of different radionuclides and high amounts of radioactive materials makes it necessary for the facilities where these procedures are conducted to evaluate the corresponding shielding to comply with the design dose limits of a facility and avoid radiological accidents as recommended and accepted in international publications, like the International Commission on Radiological Protection (ICRP) and the National Council on Radiation Protection and Measurements (NCRP). This work compares two methods to calculate the shielding necessary to guarantee que las medicine service zones be safe from ionizing radiations. The first method consists in calculating the transmission factor B to find the thickness of the material necessary to protect the zone of interest, this factor is calculated by bearing in mind the occupancy factors, workloads, use factor, and the design objective dose limit. Upon obtaining the transmission factor B, half value layer (HVL) or tenth value layer (TVL) tables are used for each construction material, obtaining the thickness of the material. The other method is the calculation of is the calculation of rates of exposure through the air Kerma rate constant, then the XCOM databases are used, which were developed by the National Institute of Standards and Technology (NITS) to obtain the attenuation coefficient, used in the law of exponential attenuation; finally, the necessary thickness of the material is obtained to reach the design objective. Finally, the principal differences between both methods are shown and an analysis is performed of the shielding optimization, seeking to set criteria to make recommendations to nuclear medicine services on optimal shielding.. Resumen La medicina nuclear es una especialidad médica que utiliza materiales radioactivos inyectados en el cuerpo para diagnóstico y tratamiento de enfermedades humanas. El uso de diferentes radionúclidos y altas cantidades de materiales radiactivos hace necesario que las instalaciones donde se realicen estos procedimientos evalúen los blindajes correspondientes para cumplir los límites de dosis de diseño de una instalación evitando así accidentes radiológicos recomendados y aceptados en las publicaciones internacionales como el ICRP (International Commision on Radiological Protection) y el NCRP (National Council on Radiation Protection and Measurments). En este trabajo se comparan dos métodos para el cálculo de los blindajes necesarios para garantizar que las zonas del servicio de medicina sean seguras a las radiaciones ionizantes. El primer método consiste en calcular el factor de transmisión B para hallar el espesor del material necesario para proteger la zona de interés, este factor se calcula teniendo en cuenta los factores de ocupación, cargas de trabajo, factor de uso y el límite de dosis objetivo de diseño. Una vez obtenido el factor de transmisión B se usan las tablas de HVL (Half Value Layer) o TVL (Tenth Value Layer) para cada material de construcción obteniéndose el espesor del material. El otro método es el cálculo de las tasas de exposición por medio de la constante de la tasa de Kerma en Aire, luego se usan las bases de datos (XCOM) desarrolladas por NITS (National Institute of Standards and Technology) para obtener el coeficiente de atenuación que son utilizados en la ley exponencial de atenuación; finalmente, se obtiene el espesor de material necesario para alcanzar el objetivo de diseño. Finalmente, se muestran las principales diferencias entre los dos métodos y se hace un análisis de la optimización de los blindajes buscando tener criterios para hacer recomendaciones a los servicios de medicina nuclear sobre blindajes óptimos.
Evaluation of Shielding Barrier of a Computed Tomography Unit
Fudma Journal of Sciences, 2020
Recently, concerns have been expressed on the radiological standards of Computed Tomography (CT) units in terms of radiation protection. This study was carried out in the CT scan unit of General Amadi Rimi Specialist Hospital (GARSH), Katsina, Nigeria. The study aimed to evaluate the radiation shielding barrier of a Computed Tomography unit of GARSH, Katsina, Nigeria. The main objective of this study is to determine the shielding barrier thickness required to attenuate the unshielded radiation. Calculations of the shielding barrier thickness were carried out using XRAYBARR software. The total workload for the CT modality was found to be 48.32 mA-min per week for an average of 32 patient per week. The shielding barrier thickness required in attenuating the unshielded radiation dose for wall 1, 2, 3, 4, control area, floor and ceiling was 155.1, 146.8, 112.5, 98.10, 98.10, 193.0 and 128.0 mm thickness concrete, respectively. The already constructed shielding barrier thickness was found to be 244mm thickness concrete. Ratio of the calculated barrier thickness to the designed barrier thickness was less than 1. This showed that the constructed shielding barrier thickness was adequate and safe. The area monitoring of the strategic areas in the CT unit was carried out using calibrated radiation survey meter. The result revealed that, the background and leakage radiation doses were within the recommended dose limit. High radiation dose was recorded at the door of the CT scan room. It was recommended that the occupational workers should always use thyroid shield and light-lead glasses in the controlled area.
Determination of shielding requirements for mammography
Shielding requirements for mammography when considerations are to be given to attenuation by compression paddle, breast tissue, grid and image receptor ͑intervening materials͒ has been investigated. By matching of the attenuation and hardening properties, comparisons are made between shielding afforded by breast tissue materials ͑water, Lucite and 50%-50% adipose-glandular tissue͒ and some materials considered for shielding diagnostic x-ray beams, namely lead, steel and gypsum wallboard. Results show that significant differences exist between the thickness required to produce equal attenuation and that required to produce equal hardening of a given incident beam. While attenuation equivalent thickness produces equal exposure, it does not produce equal hardening. For shielding purposes, equivalence in exposure reduction without equivalence in penetrating power of an emerging beam does not amount to equivalence in shielding affordable by two different materials. Presented are models and results of sample calculations of additional shielding requirements apart from that provided by intervening materials. The shielding requirements for the integrated beam emerging from intervening materials are different from those for the integrated beam emerging from materials ͑lead/steel/gypsum wallboard͒ with attenuation equivalent thicknesses of these intervening materials.