Human Body Phantom Research Articles

Improved assessment of radiofrequency electromagnetic field power deposition near orthopaedic device using a bone-inclusive ASTM phantom under 1.5T and 3T MRI

Objective. A bone-inclusive ASTM phantom is proposed to improve the assessment of radiofrequency electromagnetic field (RF-EMF) power deposition near orthopedic device under 1.5 T and 3 T magnetic resonance imaging (MRI). Approach. A phantom is created by introducing a cylindrical bone structure inside the American Society for Testing and Materials (ASTM) phantom. Four orthopaedic implant families—rod, nailing system, plate system, and hip replacement—are used in the study. RF-EMF power deposition (in terms of peak averaged specific absorption rate over 1 gram) near these implants are evaluated by placing these implants inside the standard ASTM phantom, the developed bone-inclusive ASTM phantom, and two anatomically representative human body phantoms, known as Duke and Ella. Numerical simulations are performed to calculate the RF-EMF power deposition near various orthopaedic devices within these phantoms. Main Results. For devices implanted inside or near bone tissue, the evaluation of RF-EMF power deposition using the developed bone-inclusive ASTM phantom shows better correlations to the human body phantoms than the ASTM phantom. This improvement is attributed to the portion of the devices implanted within the bone tissue. Significance. The bone-inclusive ASTM phantom has the different tissue of interests surrounding the implants compared to the ASTM phantom. This variation can lead to the different resonance frequency under RF-EMF exposure. This leads to better correlation of RF-EMF power deposition near orthopaedic implants inside human body, making the bone-inclusive ASTM phantom more suitable for evaluating RF-EMF power deposition than ASTM phantom in MRI scans.

Depth Dose According to Depth during Cone Beam Computed Tomography Acquisition and Dose Assessment in the Orbital Area Using a Three-Dimensional Printer

Background: Cone beam computed tomography (CBCT) is essential for correcting and verifying patient position before radiation therapy. However, it poses additional radiation exposure during CBCT scans. Therefore, this study aimed to evaluate radiological safety for the human body through dose assessment for CBCT.Materials and Methods: For CBCT dose assessment, the depth dose was evaluated using a cheese phantom, and the dose in the orbital area was evaluated using a human body phantom self-fabricated with a three-dimensional printer.Results and Discussion: The evaluation of radiation doses revealed maximum doses of 14.14 mGy and minimum doses of 6.12 mGy for pelvic imaging conditions. For chest imaging conditions, the maximum doses were 4.82 mGy, and the minimum doses were 2.35 mGy. Head imaging conditions showed maximum doses of 1.46 mGy and minimum doses of 0.39 mGy. The eyeball doses using a human body phantom model averaged at 2.11 mGy on the left and 2.19 mGy on the right. The depth dose ranged between 0.39 mGy and 14.14 mGy, depending on the change in depth for each imaging mode, and the average dose in the orbit area using a human body phantom was 2.15 mGy.Conclusion: Based on the experimental results, CBCT did not significantly affect the radiation dose. However, it is important to maintain a minimal radiation dose to optimize radiation protection following the as low as reasonable achievable principle.

A suitable procedure of dose reduction factor measurements of X-ray shields during computed tomography examination - The importance of considering positional changes of an X-ray tube

During computed tomography (CT) examinations, radio-sensitive organs located outside the field of view (FOV) are usually exposed to radiation caused by both direct and scattered X-rays. Traditionally, the use of radiation protection products has been an option for reducing exposure doses. The catalog value of the dose reduction factor (DRF) for a commercial X-ray shield is generally determined by the manufacturer using a plain X-ray irradiation system to measure the difference in dose with and without the shield. In contrast, actual shielding ability measurements during clinical CT examinations are usually evaluated using a similar equation, but it is not guaranteed that the incident directions of X-rays will be the same between the measurement data with and without a shield. The purposes of this study are to introduce a novel method for evaluating DRF by accounting for the influence of the X-ray incident direction in helical scanning and to obtain knowledge about the correctness of previously reported DRF values. Experiments pertaining to chest CT examinations were performed using a human body phantom and small-type dosimeters which consist of an optically stimulated luminescence element using Al2O3:C. A total of 100 examinations were iteratively performed, both with and without a shield. The corresponding DRF was then calculated. The novelty of the proposed analysis procedure lies in a paired analysis method, where the DRF is calculated by reorganizing numerous acquired data sets with and without the shield to pair similar incident angles of X-rays. As a result, the DRF values were estimated to be 48.5 ± 4.3%, 48.7 ± 2.7%, and 48.9 ± 1.5% based on the data results within the 10–40 data sets, 40–70 data sets, and 70–100 data sets, respectively. When the DRF values were obtained by the conventional method without applying our sorting procedure, the results were 48.4 ± 8.1%, even when the 70–100 data sets were used. This result indicates that the proposed method can analyze DRF with higher accuracy. In the example of thyroid X-ray shield, while there was no significant difference in the most probable values of DRF between the conventional and proposed methods coincidentally, we believe it is important to evaluate DRF based on a scientifically correct approach because the mathematical formulas for calculating these two values differ. In conclusion, when calculating the DRF of shielding materials during CT examination, it is imperative that data analysis considers the significant impact of differences in incident X-ray directions on the measured exposure dose data.

Dose verifications in several organs in abdominal computed tomography (CT) scan by using Al2O3 OSL dosimeters

The study investigated the dose of several organs in the computed tomography (CT) scan by using Al2O3 optically stimulated luminescent (OSL) dosimeters. The organs of right and left kidney, right pancreas, spleen and liver in an anthropomorphic human phantom were investigated for the dose received during the scan. The OSL dosimeters are embedded into custom-made wax and replace onto two selected slices of human body phantom where the selected organs are located. The phantom was scanned with by using adult abdomen protocol. The percentage differences of OSL doses reading compared to the previous study data and the international dose reference level (DRL). The doses obtained from OSL NanoDots® showed excellent agreement compared to XRQA film dosimeters with percentage differences within 5%. The doses measured by using OSL dosimeters in five organs were also within the range of the national DRL values by the Ministry of Health of Malaysia (MOH). These findings suggest that our results can be utilized to verify the doses received by internal organs during computed tomography abdomen protocols. The overall results indicated the suitability of OSL dosimeters for the indirect dose verification in the CT scan.

Design method of a focusing dielectric lens antenna and temperature increment measurement at the focusing spot

In radio wave hyperthermia therapy, array antenna configuration was mainly studied to generate a small spot at the diseased part. Array antennas have the flexibility in controlling radiation performance, such as spot positions, by using their numerous radiating elements. However, the flexibility is achieved at the expense of antenna structure complexity. On the other hand, a lens antenna can concentrate radio waves into a small spot by forming a lens shape. The simplicity of a lens antenna structure lends itself to easy handling in a practical application. Moreover, the frequency independence of the lens antenna allows for a more flexible selection of hyperthermia therapy frequencies. Therefore, the lens antenna is selected as a focusing antenna in this paper. The lens shaping method and the temperature increment measurement are the main contents of this paper. The designed lens has a diameter of 30 cm, a focusing distance of 30 cm, and a working frequency of 2.45 GHz. A thin lens design method is applied to reduce lens weight. Firstly, the focusing ability of the designed lens is ensured by comparing the spot size results of electromagnetic (EM) simulation with its theoretical value. A spot size of 1.77 cm is obtained in both cases. Next, the temperature increment is examined by EM simulations. The temperature at the 2 cm tumor was increased to 41 °C from the human body temperature of 37 °C by an input power of 10 Watts (W). For the temperature increment measurement, a tumor within human body phantom is utilized and the available input power is reduced to 4 W. The tumor temperature increased from 21.5 °C of room temperature to 24.4 °C, which was captured by a thermal imaging camera. As a result, the functionality of the lens antenna for hyperthermia therapy is verified.

Radiation shielding assessment for interventional radiology personnel: Geant4 dosimetry of lead-free compositions

The inherent biological hazards associated with ionizing radiation necessitate the implementation of effective shielding measures, particularly in medical applications. Interventional radiology, in particular, poses a unique challenge as it often exposes medical personnel to prolonged periods of high x-ray doses. Historically, lead and lead-based compounds have been the primary materials employed for shielding against photons. However, the drawbacks of lead, including its substantial weight causing personnel’s inflexibility and its toxicity, have raised concerns regarding its long-term impact on both human health and the environment. Barium tantalate has emerged as a promising alternative, due to its unique attenuation properties against low-energy x-rays, specifically targeting the weak absorption area of lead. In the present study, we employ the Geant4 Monte Carlo simulation tool to investigate various formulations of barium tantalate doped with rare earth elements. The aim is to identify the optimal composition for shielding x-rays in the context of interventional radiology. To achieve this, we employ a reference x-ray spectrum typical of interventional radiology procedures, with energies extending up to 90 keV, within a carefully designed simulation setup. Our primary performance indicator is the reduction in air kerma transmission. Furthermore, we assess the absorbed doses to critical organs at risk within a standard human body phantom protected by the shield. Our results demonstrate that specific concentrations of the examined rare earth impurities can enhance the shielding performance of barium tantalate. To mitigate x-ray exposure in interventional radiology, our analysis reveals that the most effective shielding performance is achieved when using barium tantalate compositions containing 15% Erbium or 10% Samarium by weight. These findings suggest the possibility of developing lead-free shielding solutions or apron for interventional radiology personnel, offering a remarkable reduction in weight (exceeding 30%) while maintaining shielding performance at levels comparable to traditional lead-based materials.

ADVANCED ULTRAWIDEBAND PATCH ANTENNA FOR WEARABLE AND WBAN APPLICATIONS

Present communication devices are adopting an application-centric approach with the integration of electronic gadgets into wearable accessories in recent years. This paper presents a wearable antenna with a flexible textile substrate. The design comprises a low-profile, textile-based UWB (3.1-10.6 GHz) antenna of 25 × 20 × 1 mm<sup>3</sup> size with a defected ground structure. Design antenna performance characteristics have been simulated in Computer Simulation Technology studio. It offers a gain of 4.204 dBi at 5.11 GHz frequency and 2.993 dBi at 7.39 GHz frequency using a cotton substrate with a 1.6 dielectric constant. A simulated testing of the design antenna on a human body phantom has resulted in a gain of 0.697 dBi with a return loss of -30.863dB and 1.058 VSWR at 5.3125 GHz frequency. A specific absorption rate value of 1.64 W/kg of the designed antenna for 10 g tissue shows that it is safe for the human body. The patch antenna of the paper is promising for wearable, medical imaging, tumor detection, and other wireless body area network (WBAN) biomedical applications.

Out-of-field dosimetry using a validated PHITS model and computational phantom in clinical BNCT.

The out-of-field radiation dose for boron neutron capture therapy (BNCT), which results from both neutrons and γ-rays, has not been extensively evaluated. To safely perform BNCT, the neutron and γ-ray distributions inside the treatment room and the whole-body dose should be evaluated during commissioning. Although, certain previous studies have evaluated the whole-body dose in the clinical research phase, no institution providing BNCT covered by health insurance has yet validated the neutron distribution inside the room and the whole-body dose. To validate the Monte Carlo model of the BNCT irradiation room extended for the whole-body region and evaluate organ-at-risk (OAR) doses using the validated model with a human-body phantom. First, thermal neutron distribution inside the entire treatment room was measured by placing Au samples on the walls of the treatment room. Second, neutron and gamma-ray dose-rate distributions inside a human-body water phantom were measured. Both lying and sitting positions were considered. Bare Au, Au covered by Cd (Au+Cd), In, Al, and thermoluminescent dosimeters were arranged at 11 points corresponding to locations of the OARs inside the phantom. After the irradiation, γ-ray peaks emitted from the samples were measured by a high-purity germanium detector. The measured counts were converted to the reaction rate per unit charge of the sample. These measurements were compared with results of simulations performed with the Particle and Heavy Ion Transport code System (PHITS). A male adult mesh-type reference computational phantom was used to evaluate OAR doses in the whole-body region. The relative biological effectiveness (RBE)-weighted doses and dose-volume histograms (DVHs) for each OAR were evaluated. The median dose (D50% ) and near-maximum dose (D2% ) were evaluated for 14 OARs in a 1-h-irradiation process. The evaluated RBE-weighted doses were converted to equivalent doses in 2Gy fractions. Experimental results within 60cm from the irradiation center agreed with simulation results within the error bars except at±20, 30cm, and those over 70cm corresponded within one digit. The experimental results of reaction rates or γ-ray dose rate for lying and sitting positions agreed well with the simulation results within the error bars at 8, 4, 11, 7 and 7, 4, 7, 6, 5, 6 out of 11 points, respectively, for Au, Au+Cd, In, Al, and TLD. Among the detectors, the discrepancies in reaction rates between experiment and simulation were most common for Au+Cd, but were observed randomly for measurement points (brain, lung, etc.). The experimental results of γ-ray dose rates were systematically lower than simulation results at abdomen and waist regions for both positions. Extending the PHITS model to the whole-body region resulted in higher doses for all OARs, especially 0.13Gy-eq increase for D50% of the left salivary gland. The PHITS model for clinical BNCT for the whole-body region was validated, and the OAR doses were then evaluated. Clinicians and medical physicists should know that the out-of-field radiation increases the OAR dose in the whole-body region.

Spin Coated Multi‐Walled Carbon Nanotube Patch Antenna for Breast Cancer Detection

AbstractEarly detection of breast cancer can be a life‐saving measure for many patients. The inaccessibility of X‐rays, magnetic resonance imaging (MRI), and other medical facilities in many resource‐constrained areas hinders the early detection of breast cancer. In this paper, the use of a rectangular patch antenna for breast cancer detection is proposed by using multiwall carbon nanotubes (MWCNTs) as patch material. The proposed antenna is designed by CST software which is (30 × 40 × 1.66) mm in dimension. A breast model is designed including tumor and cancerous tumors by specific tissue properties for observing the antenna performance in different cases. In free space, the return loss of the designed antenna is observed at −33.414 dB. Moreover, the S11 is examined in a normal breast, a breast including a normal tumor, and a breast including a cancerous tumor is −32.641 dB, −34.94 dB, and −35.22 dB respectively. It can be utilized on a human body phantom model due to its adaptability and reduced radiation properties. The proposed antenna is miniature in size, cost‐effective, easily portable, and eco‐friendly. It can be used as a first screening tool for breast cancer patients, particularly in resource‐constrained regions.

Compact eight-shaped ISM-I band wearable antenna for wireless body area network applications

Abstract The design and analysis of the electrically small eight-shaped wearable antenna for both on- and off-body communication is proposed in this paper. An eight-shaped radiating structure is placed over the jeans substrate and an I-shaped slot is introduced in the ground plane which makes the antenna resonates at the ISM-I band (2.4 GHz). The antenna has a compact size of 0.30λ 0 × 0.20λ 0 × 0.001λ 0, where λ 0 is the free space wavelength at the resonance frequency. The impedance bandwidth (≤−10 dB) of the antenna is 6.1 % and 5.8 % in free space and presence of a human body phantom respectively. The antenna design exhibits good gain along with an improved omnidirectional radiation pattern. The specific absorption rate (SAR) of the antenna averaged over 1 g of tissue is 0.21 W/kg at 2.45 GHz which is far below the FCC standard. The paper also discusses the bending analysis and the fundamental size limitations of the small antenna, concluding that it is suitable for practical use. The simulated results of the prototype are validated by the measured results.

Evaluation of fetal absorbed doses from computed tomography examinations of pregnant patients: A systematic review

BACKGROUND: Currently, no systematic data are available on fetal radiation exposure as a result of radiographic studies during pregnancy. Consequently, there are no approved methods of its calculation that can be used in clinical practice. It is especially relevant for computed tomography scans as it is a widely used and highly informative method of diagnostic imaging associated with high exposure levels.
 AIM: to systematize currently available data on radiation dose absorbed by the fetus from computed tomography scans in pregnant women.
 MATERIALS AND METHODS: The search for publications in Russian and English was conducted in PubMed/Medline, Google Scholar and еLibrary. The final analysis included 12 papers including 8 studies using human body phantoms, 3 retrospective studies and one prospective clinical study.
 RESULTS: Abdominal and pelvic computed tomography scans as well as whole-body scans were found to be associated with the highest fetal radiation exposure. However, in none of the publications the fetal exposure limit was exceeded.
 CONCLUSION: Clinically indicated non-contrast-enhanced computed tomography scans in pregnant women are not likely to be associated with the fetal absorbed doses that exceed the limit of 100 mGy regardless of the scanned area. However, this limit might be exceeded in case of performing multiple studies or if multiphase abdominal or pelvic computed tomography scans, or whole-body computed tomography scans are performed in patients with multiple trauma. In these cases, a decision regarding the need for these investigations should be made by a multi-disciplinary team (including radiation safety specialists, diagnostic radiologists and clinicians) based on the results of additional risk assessment.

On-Body Low-Profile Compact AMC-Integrated Wideband Antenna for Body Area Network Applications

This communication presents a wideband and a low-profile flexible wearable antenna intended to operate at a 2.45 GHz WBAN band. The suggested antenna comprises a CPW-fed monopole antenna backed by an artificial magnetic conductor (AMC) to act as a reflector. The latest AMC-integrated design uses R03003 as a dielectric substrate. The suggested design features an impedance bandwidth of 71.03% (1.87–3.93 GHz) with a gain value of 3.62 dBi and has a compact footprint of 40 × 40 mm2. The incorporation of wideband AMC with a monopole antenna leads to bandwidth enhancement and covers the 3.5 GHz WiMAX band. Simulation and experimental studies provide evidence that in the case of structural deformities and human body loading, the suggested AMC-integrated antenna is stable and shows superior efficiency relative to the traditional monopole antenna. Furthermore, numerical analysis demonstrates that the amount of radiation AMC-integrated antenna decreases tremendously in terms of specific absorption rate for various bodily attachment scenarios. Three body templates with various compositions and forms were used to study the effects of the antenna on bodily attachment. Extensive experiments on human body phantoms and bodily attachment are also conducted and the results are presented. The suggested AMC-integrated design thus confirms a promising contender for portable wearable wireless applications.

Design and analysis of a super compact UWB antenna for accurate detection of breast tumors using monostatic radar‐based microwave imaging technique

AbstractThis article proposes a low‐profile ultra‐wideband (UWB) antenna for breast tumor detection using the monostatic radar‐based microwave imaging (RBMI) technique. The proposed UWB antenna consists of a circular patch and ground plane along with a modified tapered feed line having a total size of 13 × 9 × 1.6 mm3. The designed antenna operates from 4 to 11 GHz based on a −10 dB reflection coefficient with a peak gain of 9.5 dBi at 4.8 GHz. Experimental validation is carried out after fabricating the prototype of the UWB antenna and the breast mimic. The measured backscattered signals are captured using the vector network analyzer (E‐5063A) by keeping the antenna at 10 mm from the breast phantom. After that, post‐processing of the measured data is done to detect the exact depth and location of the malignant tissue. The proposed antenna uses UWB band frequency of operation because it has some unique features, that is, it provides immunity to multipath fading, has a simple design, has a low cost of fabrication, and has biological friendliness. Moreover, due to the proposed antenna's resonance at a lower resonant frequency better depth of penetration is achieved in human body phantoms and the proposed antenna provides specific absorption rates (SAR) of 0.877 W/kg over 1 g of tissue at 4.8 GHz, which is an acceptable limit for SAR as per FCC guidelines. Therefore, the proposed antenna and monostatic RBMI technique are good candidates for breast tumor detection.

Properties of the SSIM metric in medical image assessment: correspondence between measurements and the spatial frequency spectrum.

In radiological imaging, the acquisition of the required diagnostic image quality under optimized conditions is important. Although techniques based on structural similarity (SSIM) have been investigated, concerns have been raised regarding their application to medical images. This study aims to clarify the properties of SSIM as an image quality index in medical images, focusing on digital radiography and verifying the correspondence between the evaluation results obtained by SSIM and the frequency spectrum. The analysis target was chest X-ray images of a human-body phantom. Various types of processing were applied to the images, and several regions of interest (ROIs) were used in local areas for analysis. The SSIM was measured using unprocessed data as a reference while changing the calculation parameters, and the spatial frequency spectrum of each local region was analyzed. Thus, a significant effect of ROI size was observed when calculating the SSIM. This indicates that larger the ROI size leads to SSIM values closer to 1 for all analysis conditions. In addition, a relationship between the size of the ROI in the analysis and the frequency components is demonstrated. It was shown that careful attention should be paid to the structures included in the ROI, and parameter settings should be reconsidered. Furthermore, when using SSIM to assess medical images, a multiscale SSIM method obtained by changing the ROI size would be useful.

A wearable active-type X-ray dosimeter having novel functions to derive both incident direction and absolute exposure dose

Currently, interventional radiology (IVR) procedures using X-ray fluoroscopic equipment are widely used to perform medical diagnosis and treatment, and during these procedures medical staff are often exposed to scattered X-rays. This study aims to propose a concept of a novel dosimetric system that can analyze both the X-ray incident angle and radiation exposure dose simultaneously. Our dosimeter consists of three active-type detectors. Absolute dose rates can be determined by the center detector, and the side detectors can derive incident direction. Incident windows of the side detectors have symmetrically-sloped titanium filters to enlarge the angular dependence. These filters create a difference in the responses measured by the left and right detectors when X-rays are incident to a centered position; from this, the incident angle of the X-rays can be calculated. To verify the concept, basic experiments using a clinical fluoroscopic system were performed. It was found that our dosimeter can derive the incident angle of X-rays between ± 50° and determine the absolute dose with proper angular dependence correction. Furthermore, a fluoroscopic procedure was mimicked using a human body phantom and a mannequin on which our dosimeter with a wearable optical camera was placed. Although commercial dosimeters can determine exposure doses with a systematic uncertainty of ± 13.4%, our dosimetric system can analyze absolute exposure doses with a systematic uncertainty of ± 4.2%.

Low-Profile Meander Line Multiband Antenna for Wireless Body Area Network (WBAN) Applications with SAR Analysis

In this work, we propose a novel multiband meander line antenna that can operate at three different frequency bands and offer suitable performance for wireless body area network (WBAN) applications. The net geometry of the antenna is 36 × 30 × 1.524 mm3. The proposed low-profile antenna is analytically modeled and designed in full wave ANSYS HFSS using Rogers TMM4 as the substrate, followed by in-lab prototyping. The designed antenna resonates at 4.5 GHz, 5 GHz, and 5.8 GHz and maintains positive gain, efficiency, and acceptable specific absorption rates at each resonant band. The effectiveness of the antenna for WBAN applications is demonstrated using an in-lab manufactured phantom. The fabrication process of the phantom is described, and dielectric characterization of the phantom mimicking different human tissue layers is presented. Considering results with and without human body phantoms available in the full wave ANSYS HFSS tool, a comparative analysis between simulated and measured antenna parameters concludes this work. Both the simulated and measured results show good agreement.

Relative Error between Organ Doses and Size-specific Dose Estimates for a Specific Location When the Mean CTDIvol Value Is Used for Calculation

Size-specific dose estimates (SSDEs) are dose indices that account for differences in body shape in computed tomography (CT) scans, allowing the evaluation of approximate absorbed doses in any cross section that could not be obtained with the volume CT dose index (CTDIvol). When using automatic exposure control (AEC), CTDIvol is modulated in the body axis direction, but the value displayed after the examination is the mean CTDIvol for the entire scan, and it is expected that the SSDE value will change depending on which value is used in the calculation. In this study, using a human body phantom, we examined the influence of whether the mean CTDIvol or the modulation value for each slice is used to calculate the SSDE on local organ dose evaluation. A program to calculate water equivalent diameter according to the procedure in the American Association of Physicists in Medicine Report No. 220 was developed and compared. As a result, SSDE calculated using the mean CTDIvol (local-SSDEmean) overestimated organ doses in the lung region by 18%-56% compared with those calculated by a web system for evaluating CT exposure doses (WAZA-ARIv2, Japan). In contrast, local-SSDEmodulated, which was calculated using the modulated value of the CTDIvol, was able to estimate the organ dose with a relative error of 10%-13%. The average local-SSDE over the entire body axis direction was not significantly different between the two methods, regardless of which method was used for CTDIvol. If the mean CTDIvol is stored in the Digital Imaging and Communications in Medicine (DICOM) header tag (0018, 9345) of the CT image and the modulated CTDIvol value is not available for each slice, the calculated local SSDE will contain many errors and will not correctly reflect the organ doses at the scan region. In such cases, it is available to use the method of evaluating local organ doses by multiplying the SSDE, which is the average of the SSDE for the entire scan, by a factor for each organ.

Efficacy of L-shaped Shielding in Interventional Radiology by Transradial Approach and Consideration of Methods for Appropriate Use

The present study investigated how effective an L-shaped shield was, depending on its position, in reducing a doctor's exposure to radiation during catheterization to access the transradial approach (TRA). The shield's effectiveness was evaluated by measuring the air kerma where the doctor stood under four conditions: with and without the shield, and with and without the shield in conjunction with conventional protection. To enable the shield to be positioned correctly in clinical practice, an illustrated instruction decal affixable to the shield's doctor-facing surface was produced, and the effectiveness of the decal was verified by means of a crossover test in which, as subjects of the study, different nurses set up the shield with and without the decal affixed to it. In the test, in which a human body phantom was used, the C-arm set at the PA angle, and the shield positioned 10 cm from the axilla of the phantom, the shield's effectiveness at 100 cm, 130 cm, and 160 cm above the floor where the doctor stood was 55%, 77%, and 47%, respectively. The effectiveness increased when the shield was positioned closer to the axilla. A significant difference in the positioning of the shield by the subjects was observed depending on whether or not the decal was affixed ( p<0.05, Wilcoxon signed-rank test), indicating that the use of the decal improved the positioning. It was concluded that, positioned correctly, the shield could effectively reduce the doctor's exposure to radiation during TRA.

Accuracy of patient dose estimation in cone beam computed tomography in breast irradiation by size-specific dose estimates with position correction.

This study aims to investigate the effects of the position correction of size-specific dose estimates (SSDE) on patient dose estimation in cone beam computed tomography (CBCT). The relationship between the phantom position and absorbed dose in the right breast was studied using optically stimulated luminescence dosimeters and a simulated human body phantom. The effect of position correction for CT dose index (CTDI) on SSDE was investigated in 51 patients who underwent right breast irradiation by comparing the SSDE with position correction and SSDE without position correction. The absorbed dose in the right breast tended to decrease by 10.2% as the phantom was placed away from the center of CBCT. The mean and standard deviation of SSDE were 2.54±0.29 and 2.92±0.30 mGy with and without position correction, respectively. The SSDE with position correction was 13.1% lower than that without position correction (p<0.05). SSDE was different when the patient's torso center was located at the isocenter of CBCT, and when it was not. The same tendency was seen in the case of the breast. Therefore, if the center of the patient is not at the acquisition center of the CT scanner, position correction is required when estimating SSDE.

Thyroid dose reduction shield with the generation of less artifacts used for fast chest CT examination

Fast chest CT scans with high-pitch factors are effective to reduce motion artifacts, but the over-ranging effect may increase harmful radiation exposure to organs which are located near the outside of the imaging area. This becomes a particular problem during chest CT imaging when managing the radiation dose to the radio-sensitive thyroid, which is located around the upper end of the imaging area. The use of an X-ray shielding material can reduce the exposure dose to the thyroid. However, when the shielding is performed using metal foil, metal artifacts definitely appear, and they interfere with the CT image. To solve this problem, we developed a novel less-artifact thyroid shield in which fine bismuth oxide particles are embedded in low-density polyurethane (PU) foam. This study aims to present the usefulness of our X-ray shield through experimentation using a human body phantom. Three kinds of thyroid shields were used: a commercially-available lead foil as a reference, investigational clay products to evaluate the proper amount of the fine bismuth oxide particles, and bismuth PU shields which are proposed in this study. Furthermore, a bismuth PU shield with an added PU spacer was fabricated for the further suppression of the artifacts. Under clinical conditions, shielding ability and image quality were evaluated. Thyroid doses were measured using small-type OSL dosimeters, and the dose reduction rates were determined. In addition, the image qualities of the thyroid and lung regions were evaluated using a contrast-to-noise ratio (CNR) and an artifact index (AI). When the thyroid is outside the scanning region, thyroid exposure without the shield was caused by over-ranging X-rays and showed 11 mGy. When applying bismuth with an effective mass thickness of 0.12 g/cm2 to the bismuth PU shield, the thyroid exposure dose was reduced by half. In addition, we confirmed that if this shield enters the scanning region through accident, the AI would be less than 10. Also, when using our thyroid shield, the occurrence of metal artifacts was drastically suppressed. In conclusion, our thyroid shield can reduce the radiation exposure dose in half while maintaining acceptable image quality. This is a valuable tool in solving the issue of radiation exposure when performing fast chest CT scans. The shield has breathability and flexibility, and patients can apply the shield to their necks by themselves.