Virtual Anthropomorphic Phantoms Research Articles

Estimation of doses absorbed by the thyroid and salivary glands, eyes, and brains of pediatric dental patients

In addition to the quality of the image, radiological protection of the patient must be considered to ensure an adequate diagnosis in dental radiology, especially in regard to those parts of the patient's body that are close to the radiation beam, such as the thyroid, salivary glands, and brain. In this work, the doses absorbed by the thyroid, salivary glands, eyes and brain of pediatric dental patients undergoing radiographic examinations are estimated using MCNP 6.2 coupled with virtual anthropomorphic phantoms, based on information from dental scenarios with a periapical X-ray unit. The absorbed doses were estimated for five- and 10-year-old male and female children. In the occlusal position, a higher absorbed dose to the thyroid was found for a five-year-old patient, whereas in the molar tube position, the brain was found to receive a higher absorbed dose for five- and 10-year-old patients. The results obtained here, expressed in terms of the absorbed dose, indicate that the beam direction and the use of different image acquisition techniques strongly influence the entrance dose values for the organs of interest in this study.

Breast density quantification in dual-energy mammography using virtual anthropomorphic phantoms.

Breast density is a significant risk factor for breast cancer and can impact the sensitivity of screening mammography. Area-based breast density measurements may not provide an accurate representation of the tissue distribution, therefore volumetric breast density (VBD) measurements are preferred. Dual-energy mammography enables volumetric measurements without additional assumptions about breast shape. In this work we evaluated the performance of a dual-energy decomposition technique for determining VBD by applying it to virtual anthropomorphic phantoms. The dual-energy decomposition formalism was used to quantify VBD on simulated dual-energy images of anthropomorphic virtual phantoms with known tissue distributions. We simulated 150 phantoms with volumes ranging from 50 to 709mL and VBD ranging from 15% to 60%. Using these results, we validated a correction for the presence of skin and assessed the method's intrinsic bias and variability. As a proof of concept, the method was applied to 14 sets of clinical dual-energy images, and the resulting breast densities were compared to magnetic resonance imaging (MRI) measurements. Virtual phantom VBD measurements exhibited a strong correlation (Pearson's ) with nominal values. The proposed skin correction eliminated the variability due to breast size and reduced the bias in VBD to a constant value of -2%. Disagreement between clinical VBD measurements using MRI and dual-energy mammography was under 10%, and the difference in the distributions was statistically non-significant. VBD measurements in both modalities had a moderate correlation (Spearman's =0.68). Our results in virtual phantoms indicate that the material decomposition method can produce accurate VBD measurements if the presence of a third material (skin) is considered. The results from our proof of concept showed agreement between MRI and dual-energy mammography VBD. Assessment of VBD using dual-energy images could provide complementary information in dual-energy mammography and tomosynthesis examinations.

Occupational exposures in PET procedures with 18F-FDG in adult and pediatric patients

Diagnosis through positron emission tomography (PET) is an increasingly used procedure in cerebral, cardiac and especially oncology diseases. It is performed in nuclear medicine clinics, mainly using 18F-Fluorodeoxyglucose (18F-FDG), which has one of the longest half-lives among positron emitters. The gamma rays, produced in the annihilations, require strict radiation control to guarantee the safety of the occupationally exposed individuals working in PET exam facilities. To evaluate occupational exposures, in this study, the MCNPX2.7.0 radiation transport code was used. The professionals were represented by the FASH3 (female) and MASH3 (male) adult virtual anthropomorphic phantoms, which have anthropometric characteristics like those of real individuals. Four exposure scenarios were modeled: radiopharmaceutical preparation, administration to the patient, patient follow-up, and patient placement in PET equipment. The results are presented in terms of the mean effective dose by PET procedure (μSv/procedure) and the mean effective dose by radiopharmaceutical activity (nSv/MBq). Using the set of conversion coefficients presented in this study, it is possible to calculate the absolute values of effective doses for nuclear medicine professionals who are in contact with the radioactive material or the patient. The differences between our study and the literature were only 3%. The effective occupational doses, with an adult patient, were 14% higher than those with pediatric patients.

Monte Carlo evaluation of occupational exposure during uterine artery embolization.

Uterine fibroids affect women mainly of childbearing age, an alternative for the treatment of these fibroids is uterine artery embolization (UAE), a minimally invasive procedure which uses fluoroscopy, providing radiation doses often high, due to the fact that professionals remain in the room throughout the procedure. In this work, equivalent and effective doses were evaluated for the main physician, for the assistant and for the patient during the UAE procedure. Doses were calculated using computer simulation with the Monte Carlo Method, and virtual anthropomorphic phantoms, in a typical scenario of interventional radiology with field sizes of 20×20, 25×25 and 32×32cm2, tube voltages of 70, 80, 90 and 100kV, and projections of LAO45, RAO45 and PA. The results showed that the highest doses received by the professionals were for the LAO45 projection with 32×32cm2 field size and 100kV tube voltage, which is in accordance with the existing literature. The highest equivalent doses, without the protective equipment, were in the eyes, skin, breast and stomach for the main physician, and for the assistant they were in the eyes, breast, thyroid and skin. When she used the protective equipment, the highest equivalent doses for the main physician were on the skin, brain, bone marrow and bone surface, and for the assistant they were on the skin, brain, red bone marrow and bone surface. Effective doses increased up to 3186% for the main physician, and 2462% for the assistant, without protective equipment, thus showing their importance.

In Silico Phase-Contrast X-Ray Imaging of Anthropomorphic Voxel-Based Phantoms

Propagation-based phase-contrast X-ray imaging is an emerging technique that can improve dose efficiency in clinical imaging. In silico tools are key to understanding the fundamental imaging mechanisms and develop new applications. Here, due to the coherent nature of the phase-contrast effects, tools based on wave propagation (WP) are preferred over Monte Carlo (MC) based methods. WP simulations require very high wave-front sampling which typically limits simulations to small idealized objects. Virtual anthropomorphic voxel-based phantoms are typically provided with a resolution lower than imposed sampling requirements and, thus, cannot be directly translated for use in WP simulations. In the present paper we propose a general strategy to enable the use of these phantoms for WP simulations. The strategy is based on upsampling in the 3D domain followed by projection resulting in high-resolution maps of the projected thickness for each phantom material. These maps can then be efficiently used for simulations of Fresnel diffraction to generate in silico phase-contrast X-ray images. We demonstrate the strategy on an anthropomorphic breast phantom to simulate propagation-based phase-contrast mammography using a laboratory micro-focus X-ray source.

Evaluation of fetal, medical and occupational exposure in ERCP procedures using Monte Carlo simulation and virtual anthropomorphic phantoms

In this study, computational modeling was applied to evaluate medical and occupational exposure, to ionizing radiation, during the Endoscopic Retrograde Cholangiopancreatography (ERCP) procedure of a pregnant woman in the second gestational trimester. The fetal dose evaluation and the construction of a photon fluence map inside the procedure room were also performed. The medical staff and patient were represented by virtual anthropomorphic phantoms. These phantoms were incorporated to the radiation transport code MCNPX (version 2.7.0). The photon beam was projected on the right lateral lower section of the liver of the patient, producing a FOV of 15×15 cm2. The spectral influence was evaluated using tube voltages of 70 kVp and 80 kVp with a total filtration of 5 mmAl. The influence of the suspended shield, lead curtain and fetal shield were evaluated on the Conversion Coefficients for Equivalent Dose (CC[HT]) and Effective Dose (CC[E]) for the medical staff and patient. The removal of the lead curtain and suspended shield was considered the most critical configuration to the medical staff. In this situation, an increase up to 633% in the CC[HT]eye lens and 900% in CC[E], for the medical staff, was reached. The CC[E]Patient ranged between 0.13 mSv/Gy.cm2 (70 kVp with all protective devices) and 0.15 mSv/Gy.cm2 (80 kVp without fetal shield) and the values obtained are in agreement with the literature. The CC[HT]fetus oscillated between 2.2E-1 mSv/Gy.cm2 (70 kV with fetal shield) and 2.7E-1 mSv/Gy.cm2 (80 kV without fetal shield). The outcomes of this work are useful in the prior monitoring of the radiation doses and risks, and a reduction on these may be reached for the medical team and patient, which is a complicated arrangement in ERCP procedures.

Computational dosimetry in a pediatric i-CAT procedure using virtual anthropomorphic phantoms

The craniofacial structure is three-dimensional, and for a better visualization of these structures, Computed Tomography is often employed for diagnoses, even though being a high-cost procedure, leading to increased exposure to ionizing radiation. As a consequence, studies in dosimetry are necessary, since several radiosensitive structures are located in the head and neck, such as thyroid, crystalline and salivary glands. There is an overall consensus regarding the exposure of pediatric patients to ionizing radiation, with recommendations being that the procedures must occur with the shortest exposure time as possible, and it is only prescribed when they are effectively necessary. During the procedures, radiation effects are difficult to be measured. The use of either TL or OSL dosimeters can create artifacts within the images, and the positioning of a large number of dosimeters, necessary for the correct dose evaluation, is not feasible when it comes to a pediatric patient. Therefore pediatric virtual anthropomorphic phantoms and Monte Carlo simulations were used in this work. The absorbed and effective doses were determined during an i-CAT procedure, with 5 different fields of view, utilizing 5- and 10-year-old male virtual anthropomorphic phantoms. The results pointed out that the eye lens, salivary glands and thyroid received the highest doses. Besides, the effective dose values increase with the increasing of the FOV size, and the 5-year-old male virtual anthropomorphic phantom presented the highest effective dose values.

Dosimetric evaluation of individuals to 238U series, 232Th series and 40K radionuclides present in Brazilian ornamental rocks using computational simulation

Granites are widely used in construction and they may be potential sources of ionizing radiation, due to the presence of radionuclides such as 40Kand decay products from 238Useries and 232Thseries. These radionuclides occur in the minerals constituting the rocks. To evaluate the doses in humans exposed to 40K, and decay products from 238Useries and 232Thseries γ radiation, a room with dimensions of 4.0 × 5.0 × 2.8 m3, with uniformly distributed radiation source on the floor of granitic rocks, was computationally modeled. Adult individuals were represented in the virtual scenario by two virtual anthropomorphic phantoms FASH3 and MASH3, incorporated simultaneously in the software MCNPX 2.7.0. The mean energy deposited on each organ and tissue of FASH3 and MASH3 phantoms was determined using the MCNPX F6 tally (MeV/g/particle), while the photon flux within the room was calculated with the MCNPX F4 tally (MeV/cm2/particle). The organs that obtained the highest conversion coefficients CC[HT](Sv/Gy) were the red bone marrow (0.94), skin (0.90), breast (0.81) and bladder (0.73) for the FASH3; skin (0.89), gonads (0.88), breast (0.79) and bladder (0.70) for the MASH3. The simulated air absorbed dose rates varied between 23.4 (11%) and 25.8 (12%) nGy/h, and the annual dose rates were 0.10 (6%) and 0.11 (6%) mSv/year. These results presented acceptable statistical uncertainties and they are in agreement with the literature. Fluency of photons pointed to the central region of the room floor as the place of greatest exposure. The results showed that the organs closer to the radiation source had the highest deposited energy values. Based on the annual effective dose data obtained, it was possible to note that the values are within the literature. We believe that the methodology used will allow the investigation of any ornamental material that emits natural radiation.

Technical Note: Radiation dose reduction from computed tomography localizer radiographs using a tin spectral shaping filter.

To evaluate the possibility of lowering radiation dose from a localizer radiograph (LR) using a tin spectral shaping filter and to investigate the effect of this adaptation on the radiation dose and image quality of subsequent computed tomography (CT) examination. The study utilized a set of semianthropomorphic abdomen phantoms, representing small, medium, and large patients. The LR scans were performed with and without a tin spectral shaping filter using various kVp/mA settings. The tube current values of spiral CT examinations following the LR were assessed to evaluate the effect of LR settings on automatic exposure control (AEC). The image quality of CT examinations with various LRs was evaluated by measuring image noise in several regions-of-interest. Organ dose values from LR scans were derived from Monte Carlo simulations performed on a set of virtual anthropomorphic phantoms and the effective dose (ED) values were calculated. The radiation dose from the LR can be strongly reduced by using a tin spectral shaping filter (P<0.001). The optimal settings of the LR scan depend on the size of the scanned subject: for small and medium size subjects, the combination of a tin spectral shaping filter with 100kVp and 20mA resulted in the lowest possible radiation dose (ED=0.007mGy) without compromising the AEC and image quality of subsequent CT. In contrast, the LR settings of 100kVp with a tin spectral shaping filter and the tube current values of 20 and 35mA in large subject (47.4cm in diameter) resulted in significant variation of the TCM values (11.1% and 8.4%, respectively) and the corresponding increase of noise by >5% in subsequent CT examination. For all investigated phantom sizes, the combination of 100Sn kV with a tin spectral shaping filter and tube current values of 75mA results in the lowest possible radiation dose, while still keeping the AEC function unchanged. The study indicated that tin spectral shaping filtration can be applied to LRs for radiation dose reduction, but such adaptation needs to take patient size into account.

Estimation of conversion coefficients for absorbed and effective doses for pediatric CT examinations in two different PET/CT scanners

Normally, during medical procedures, special attention must be given to pediatric patients when compared to adults. This is specially relevant during procedures involving ionizing radiation, as CT scans, given that children are considerably more sensitive to radiation induced stochastic effects than adults. In order to investigate the radiation doses on radiosensitive organs of pediatric patients, undergoing head, chest and abdomen CT procedures, numerical dosimetry was employed in this work. The novelty is the use of a new set of pediatric virtual anthropomorphic phantoms, coupled with Monte Carlo simulation, to determine the conversion coefficients for absorbed and effective doses. Two CT equipment were simulated, taking into account the main characteristics of those commercially available. The results were converted to conversion coefficients (mGy/100 mA) for several organs and tissues, and the highest values were obtained for the newborn phantom. This numerical approach employed a new and reliable technique for pediatric CT dosimetry.

Dose estimate for cone beam CT equipment protocols using Monte Carlo simulation in computational adult anthropomorphic phantoms

Cone beam computed tomography (CBCT) has become essential for dental diagnoses in the last decade. This is supported by its low cost and low doses, when compared to medical CT. Following this increase in CBCT procedures, it is necessary to ensure the image quality within low radiation doses to the patients. This is an especially difficult challenge in CBCT, given the number of equipment models (more than 50), radiographic techniques that may be employed, and technical information not available to the users by the manufacturers. The objective of this study was to estimate the cancer risk, effective and absorbed doses in tissues and organs for CBCT protocols intended for dental use. Monte Carlo (MC) simulations were used to estimate these quantities in tissues and organs with radiological importance, as those suggested by the International Commission of Radiological Protection (ICPR) report ICRP 103. Five different fields of view (FOV) were simulated to i-Cat Classic CBCT, using the MCNPX code. The virtual anthropomorphic phantoms FASH3 (Female Adult MeSH) and MASH3 (Male Adult MeSH) were also used. The effective dose estimative was in the range 75.15–142.20 μSv. The largest contribution to the effective dose was from the salivary glands (17%), thyroid (27%) and remainder tissues (28%). The results of this work showed that the effective and absorbed doses in tissues/organs vary according to the FOV, exposure parameters, and the positioning of the beam, relative to the radiosensitive organs. Furthermore, for the same exposure conditions, women can exceed the total risk of cancer by 26–34%, when compared to men.

Monte Carlo dosimetric evaluation in PET exams for patients with different BMI and heights

In recent years, positron emission tomography (PET), associated with multi-detector computed tomography (MDCT), has become a diagnostic technique widely disseminated to evaluate various malignant tumors and other diseases. However, during PET/CT examinations, the doses of ionizing radiation experienced by the internal organs of the patients due to 18F are unknown, and may be substantial. The aim of this study was to determine a set of S values derived from the 18F-FDG and to use them to determine the absorbed and effective doses of 8 different virtual anthropomorphic phantoms (4 of each gender). These phantoms have different Body Mass Index (BMI), to represent different anatomical characteristics of patients examined in PET. The results of the S values were calculated using the MCNPX (2.7.0) Monte Carlo code. These results were compared to the ICRP 106 reference values, obtained with mathematical anthropomorphic phantoms (MIRD model). Our results of the S values were higher than those obtained and presented at the ICRP 106, mainly due to the differences between the phantoms. The differences between the relative distances of the organs and the chemical and physical characteristics of the phantoms used in this study, in relation to mathematical model, reflected the use of a detailed set of phantoms. Therefore, the results presented in this study provide accurate and reliable data for internal dose calculations for patients undergoing PET examinations.

Occupational exposures during abdominal fluoroscopically guided interventional procedures for different patient sizes — A Monte Carlo approach

In this study we evaluated the occupational exposures during an abdominal fluoroscopically guided interventional radiology procedure. We investigated the relation between the Body Mass Index (BMI), of the patient, and the conversion coefficient values (CC) for a set of dosimetric quantities, used to assess the exposure risks of medical radiation workers. The study was performed using a set of male and female virtual anthropomorphic phantoms, of different body weights and sizes. In addition to these phantoms, a female and a male phantom, named FASH3 and MASH3 (reference virtual anthropomorphic phantoms), were also used to represent the medical radiation workers. The CC values, obtained as a function of the dose area product, were calculated for 87 exposure scenarios. In each exposure scenario, three phantoms, implemented in the MCNPX 2.7.0 code, were simultaneously used. These phantoms were utilized to represent a patient and medical radiation workers. The results showed that increasing the BMI of the patient, adjusted for each patient protocol, the CC values for medical radiation workers decrease. It is important to note that these results were obtained with fixed exposure parameters.

Estimate of S-values for children due to six positron emitting radionuclides used in PET examinations

Positron emission tomography (PET) has revolutionized the diagnosis of cancer since its conception. When combined with computed tomography (CT), PET/CT performed in children produces highly accurate diagnoses from images of regions affected by malignant tumors. Considering the high risk to children when exposed to ionizing radiation, a dosimetric study for PET/CT procedures is necessary. Specific absorbed fractions (SAF) were determined for monoenergetic photons and positrons, as well as the S-values for six positron emitting radionuclides (11C, 13N, 18F, 68Ga, 82Rb, 15O), and 22 source organs. The study was performed for six pediatric anthropomorphic hybrid models, including the newborn and 1 year hermaphrodite, 5 and 10-year-old male and female, using the Monte Carlo N-Particle eXtended code (MCNPX, version 2.7.0). The results of the SAF in source organs and S-values for all organs showed to be inversely related to the age of the phantoms, which includes the variation of body weight. The results also showed that radionuclides with higher energy peak emission produces larger auto absorbed S-values due to local dose deposition by positron decay. The S-values for the source organs are considerably larger due to the interaction of tissue with non-penetrating particles (electrons and positrons) and present a linear relationship with the phantom body masses. The results of the S-values determined for positron-emitting radionuclides can be used to assess the radiation dose delivered to pediatric patients subjected to PET examination in clinical settings. The novelty of this work is associated with the determination of auto absorbed S-values, in six new pediatric virtual anthropomorphic phantoms, for six emitting positrons, commonly employed in PET exams.

Implementation of the “Anthropomorphic Phantoms” educational module from the European EUTEMPE-RX course

Introduction Anthropomorphic phantoms play a critical role in the contemporary development of Diagnostic Radiology. The Anthropomorphic Phantom educational module has been successfully developed to provide education and training of Medical Physics Experts in the field of Radiology. Purpose The aims were to familiarize the participants with the role of the physical and virtual anthropomorphic phantoms and the possibility of performing virtual clinical trials using existing and new Diagnostic and Interventional Radiology technologies. Method The Anthropomorphic Phantoms module is one of the 12 modules of the EUTEMPE-RX course. Teaching methodology includes e-learning and face-to-face approaches. The course is organized in a blended format that includes lectures, computer-based exercises, visits to hospital for experimental work and discussion sessions. The online part was developed on SEKOIA platform and included 10 chapters with state of the art reviews in the field, introduction to software used for X-ray imaging and examples. Results The face-to-face part started on September 7, 2015 at the Technical University of Varna, and lasted one week. Lectures and practical work were delivered to seventeen participants from 14 European countries. All lectures were led by worldwide recognized researchers in the field of anthropomorphic phantoms and their use in the research and clinical practice. The focus was on the practical work and the development of a work project. All participants passed successfully the exam. Conclusions The main aims of the module were successfully obtained. Selected project works are currently under detail development and will be submitted for publication.

Volumetric x-ray coherent scatter imaging of cancer in resected breast tissue: a Monte Carlo study using virtual anthropomorphic phantoms

Breast cancer patients undergoing surgery often choose to have a breast conserving surgery (BCS) instead of mastectomy for removal of only the breast tumor. If post-surgical analysis such as histological assessment of the resected tumor reveals insufficient healthy tissue margins around the cancerous tumor, the patient must undergo another surgery to remove the missed tumor tissue. Such re-excisions are reported to occur in 20%–70% of BCS patients. A real-time surgical margin assessment technique that is fast and consistently accurate could greatly reduce the number of re-excisions performed in BCS. We describe here a tumor margin assessment method based on x-ray coherent scatter computed tomography (CSCT) imaging and demonstrate its utility in surgical margin assessment using Monte Carlo simulations. A CSCT system was simulated in Geant4 and used to simulate two virtual anthropomorphic CSCT scans of phantoms resembling surgically resected tissue. The resulting images were volume-rendered and found to distinguish cancerous tumors embedded in complex distributions of adipose and fibroglandular breast tissue (as is expected in the breast). The images exhibited sufficient spatial and spectral (i.e. momentum transfer) resolution to classify the tissue in any given voxel as healthy or cancerous. ROC analysis of the classification accuracy revealed an area under the curve of up to 0.97. These results indicate that coherent scatter imaging is promising as a possible fast and accurate surgical margin assessment technique.

Evaluation of the medical and occupational shielding in cerebral angiography using Monte Carlo simulations and virtual anthropomorphic phantoms

Abstract Cerebral angiography exams may provide valuable diagnostic information for the patients with suspect of cerebral diseases, but it may also deliver high doses of radiation to the patients and medical staff. In order to evaluate the medical and occupational expositions from different irradiation conditions, Monte Carlo (MC) simulations were employed. Virtual anthropomorphic phantoms (MASH) were used to represent the patient and the physician inside a typical fluoroscopy room, also simulated in details, incorporated in the MCNPX 2.7.0 MC code. The evaluation was carried out by means of dose conversion coefficients (CCs) for equivalent (H) and effective (E) doses normalized by the air kerma-area product (KAP). The CCs for the surface entrance dose of the patient (ESD) and equivalent dose for the eyes of the medical staff were determined, because CA exams present higher risks for those organs. The tube voltage was 80 kVp, and Al filters with thicknesses of 2.5 mm, 3.5 mm and 4.0 mm were positioned in the beams. Two projections were simulated: posterior–anterior (PA) and right-lateral (RLAT). In all situations there was an increase of the CC values with the increase of the Al filtration. The highest dose was obtained for a RLAT projection with a 4.0 mm Al filter. In this projection, the ESD/KAP and E/KAP values to patient were 11 (14%) mGy/Gy cm 2 and 0.12 (0.1%) mSv/Gy cm 2 , respectively. For the physician, the use of shield lead glass suspended and lead curtain attached to the surgical table resulted in a significant reduction of the CCs. The use of MC simulations proved to be a very important tool in radiation protection dosimetry, and specifically in this study several parameters could be evaluated, which would not be possible experimentally.

Exposures in interventional radiology using Monte Carlo simulation coupled with virtual anthropomorphic phantoms

In this work we investigated the way in which conversion coefficients from air kerma-area product for effective doses (CCE) and entrance skin doses (CCESD) in interventional radiology (IR) are affected by variations in the filtration, projection angle of the X-ray beam, lead curtain attached to the surgical table, and suspended shield lead glass in regular conditions of medical practice. Computer simulations were used to model an exposure scenario similar to a real IR room. The patient and the physician were represented by MASH virtual anthropomorphic phantoms, inserted in the MCNPX 2.7.0 radiation transport code. In all cases, the addition of copper filtration also increased the CCE and CCESD values. The highest CCE values were obtained for lateral, cranial and caudal projections. In these projections, the X-ray tube was located above the table, and more scattered radiation reached the middle and upper portions of the physician trunk, where most of the radiosensitive organs are located. Another important result of this study was to show that the physician's protection is 358% higher when the lead curtain and suspended shield lead glasses are used. The values of CCE and CCESD, presented in this study, are an important resource for calculation of effective doses and entrance skin doses in clinical practice.

Poster #T208 PROACTIVE: EXPLORING LONGITUDINAL SYMPTOM COURSE TO UNDERSTAND OUTCOMES IN LAI-ORAL COMPARISONS

Cerebral angiography exams may provide valuable diagnostic information for the patients with suspect of cerebral diseases, but it may also deliver high doses of radiation to the patients and medical staff. In order to evaluate the medical and occupational expositions from different irradiation conditions, Monte Carlo (MC) simulations were employed. Virtual anthropomorphic phantoms (MASH) were used to represent the patient and the physician inside a typical fluoroscopy room, also simulated in details, incorporated in the MCNPX 2.7.0 MC code. The evaluation was carried out by means of dose conversion coefficients (CCs) for equivalent (H) and effective (E) doses normalized by the air kerma-area product (KAP). The CCs for the surface entrance dose of the patient (ESD) and equivalent dose for the eyes of the medical staff were determined, because CA exams present higher risks for those organs. The tube voltage was 80 kVp, and Al filters with thicknesses of 2.5 mm, 3.5 mm and 4.0 mm were positioned in the beams. Two projections were simulated: posterior–anterior (PA) and right-lateral (RLAT). In all situations there was an increase of the CC values with the increase of the Al filtration. The highest dose was obtained for a RLAT projection with a 4.0 mm Al filter. In this projection, the ESD/KAP and E/KAP values to patient were 11 (14%) mGy/Gy cm2 and 0.12 (0.1%) mSv/Gy cm2, respectively. For the physician, the use of shield lead glass suspended and lead curtain attached to the surgical table resulted in a significant reduction of the CCs. The use of MC simulations proved to be a very important tool in radiation protection dosimetry, and specifically in this study several parameters could be evaluated, which would not be possible experimentally.

Whole body counter calibration using Monte Carlo modeling with an array of phantom sizes based on national anthropometric reference data

During construction of the whole body counter (WBC) at the Children's Nutrition Research Center (CNRC), efficiency calibration was needed to translate acquired counts of 40K to actual grams of potassium for measurement of total body potassium (TBK) in a diverse subject population. The MCNP Monte Carlo n-particle simulation program was used to describe the WBC (54 detectors plus shielding), test individual detector counting response, and create a series of virtual anthropomorphic phantoms based on national reference anthropometric data. Each phantom included an outer layer of adipose tissue and an inner core of lean tissue. Phantoms were designed for both genders representing ages 3.5 to 18.5 years with body sizes from the 5th to the 95th percentile based on body weight. In addition, a spherical surface source surrounding the WBC was modeled in order to measure the effects of subject mass on room background interference. Individual detector measurements showed good agreement with the MCNP model. The background source model came close to agreement with empirical measurements, but showed a trend deviating from unity with increasing subject size. Results from the MCNP simulation of the CNRC WBC agreed well with empirical measurements using BOMAB phantoms. Individual detector efficiency corrections were used to improve the accuracy of the model. Nonlinear multiple regression efficiency calibration equations were derived for each gender. Room background correction is critical in improving the accuracy of the WBC calibration.