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This work provides dose coefficients necessary to reconstruct doses used in epidemiological studies of tuberculosis patients treated from the 1930s through the 1960s, who were exposed to diagnostic imaging while undergoing treatment. We made use of averaged imaging parameters from measurement data, physician interviews, and available literature of the Canadian Fluoroscopy Cohort Study and, on occasion, from a similar study of tuberculosis patients from Massachusetts, United States, treated between 1925 and 1954. We used computational phantoms of the human anatomy and Monte Carlo radiation transport methods to compute dose coefficients that relate dose in air, at a point 20 cm away from the source, to absorbed dose in 58 organs. We selected five male and five female phantoms, based on the mean height and weight of Canadian tuberculosis patients in that era, for the 1-, 5-, 10-, 15-year old and adult ages. Using high-performance computers at the National Institutes of Health, we simulated 2,400 unique fluoroscopic and radiographic exposures by varying x-ray beam quality, field size, field shuttering, imaged anatomy, phantom orientation, and computational phantom. Compared with previous dose coefficients reported for this population, our dosimetry system uses improved anatomical phantoms constructed from computed tomography imaging datasets. The new set of dose coefficients includes tissues that were not previously assessed, in particular, for tissues outside the x-ray field or for pediatric patients. In addition, we provide dose coefficients for radiography and for fluoroscopic procedures not previously assessed in the dosimetry of this cohort (i.e. pneumoperitoneum and chest aspirations). These new dose coefficients would allow a comprehensive assessment of exposures in the cohort. In addition to providing newly derived dose coefficients, we believe the automation and methods developed to complete these dosimetry calculations are generalizable and can be applied to other epidemiological studies interested in an exposure assessment from medical x-ray imaging. These epidemiological studies provide important data for assessing health risks of radiation exposure to help inform the current system of radiological protection and efforts to optimize the use of radiation in medical studies. [ABSTRACT FROM AUTHOR]

Radiation dosimetry is an essential input for epidemiological studies of radiotherapy patients aimed at quantifying the dose–response relationship of late-term morbidity and mortality. Individualised organ dose must be estimated for all tissues of interest located in-field, near-field, or out-of-field. Whereas conventional measurement approaches are limited to points in water or anthropomorphic phantoms, computational approaches using patient images or human phantoms offer greater flexibility and can provide more detailed three-dimensional dose information. In the current study, we systematically compared four different dose calculation algorithms so that dosimetrists and epidemiologists can better understand the advantages and limitations of the various approaches at their disposal. The four dose calculations algorithms considered were as follows: the (1) Analytical Anisotropic Algorithm (AAA) and (2) Acuros XB algorithm (Acuros XB), as implemented in the Eclipse treatment planning system (TPS); (3) a Monte Carlo radiation transport code, EGSnrc; and (4) an accelerated Monte Carlo code, the x-ray Voxel Monte Carlo (XVMC). The four algorithms were compared in terms of their accuracy and appropriateness in the context of dose reconstruction for epidemiological investigations. Accuracy in peripheral dose was evaluated first by benchmarking the calculated dose profiles against measurements in a homogeneous water phantom. Additional simulations in a heterogeneous cylinder phantom evaluated the performance of the algorithms in the presence of tissue heterogeneity. In general, we found that the algorithms contained within the commercial TPS (AAA and Acuros XB) were fast and accurate in-field or near-field, but not acceptable out-of-field. Therefore, the TPS is best suited for epidemiological studies involving large cohorts and where the organs of interest are located in-field or partially in-field. The EGSnrc and XVMC codes showed excellent agreement with measurements both in-field and out-of-field. The EGSnrc code was the most accurate dosimetry approach, but was too slow to be used for large-scale epidemiological cohorts. The XVMC code showed similar accuracy to EGSnrc, but was significantly faster, and thus epidemiological applications seem feasible, especially when the organs of interest reside far away from the field edge. [ABSTRACT FROM AUTHOR]

The risks associated with exposure to external fields of ionising radiation are important to quantify in order to provide guidance towards public and worker protection. In Publication 116 of 2010, the International Commission on Radiological Protection (ICRP) published adult male and female fluence-to-dose coefficients (henceforth referred to as dose coefficients) for external exposures to six types of idealised neutron fields. However, ICRP 116 dose coefficients are not appropriate for applications involving children due to their smaller body weight and stature. Our current work details dose coefficient calculations for children and young adolescents using the UF-NCI pediatric hybrid phantoms at all neutron energies considered in ICRP 116 (0.001 eV to 10 GeV); those dose coefficients with energy up to 150 MeV are discussed. The hybrid UF-NCI phantoms are divided into five separate age groups: newborn, 1, 5, 10, and 15 years. For these phantoms, we calculated dose coefficients for the six idealised neutron fields for 28 organs, two bone tissues, and the overall whole body effective dose. All calculations were performed using the MCNP6 radiation transport code. To validate our methodology, we first calculated dose coefficients for the ICRP adult male and female phantoms and confirmed our ability to reproduce the values published within ICRP 116. The same methodology was then applied to calculate dose coefficients for the UF-NCI pediatric phantoms. Energy-dependent trends were observed in the neutron dose coefficients for pediatric phantoms: below 100 keV, dose increases with phantom age (a proxy for body size); however, above 100 keV, the opposite trend was observed. Comparisons between field geometries showed varying trends depending on the location of the organ within the body. Explanations for these trends are also explored within. Our results are the first comprehensive set of neutron dose coefficients derived for children and young adolescents using the newest generation of hybrid phantoms. The primary application of the pediatric neutron dose coefficients presented in this work will be for a planned effort to update the dosimetry for the Japanese atomic bomb survivors. [ABSTRACT FROM AUTHOR]

Organ and effective dose coefficients have been calculated for the International Commission on Radiological Protection (ICRP) reference pediatric phantoms externally exposed to mono-energetic photon radiation (x- and gamma-rays) from 0.01 to 20 MeV. Calculations used Monte Carlo radiation transport techniques. Organ dose coefficients, i.e., organ absorbed dose per unit air kerma (Gy/Gy), were calculated for 28 organs and tissues including the active marrow (or red bone marrow) for 10 phantoms (newborn, 1 year, 5 year, 10 year, and 15 year old male and female). Radiation exposure was simulated for 33 photon mono-energies (0.01–20 MeV) in six irradiation geometries: antero-posterior (AP), postero-anterior, right lateral, left lateral, rotational, and isotropic. Organ dose coefficients for different ages closely agree in AP geometry as illustrated by a small coefficient of variation (COV) (the ratio of the standard deviation to the mean) of 4.4% for the lungs. The small COVs shown for the effective dose and AP irradiation geometry reflect that most of the radiosensitive organs are located in the front part of the human body. In contrast, we observed differences in organ dose coefficients across the ages of the phantoms for lateral irradiation geometries. We also observed variation in dose coefficients across different irradiation geometries, where the COV ranges from 18% (newborn male) to 38% (15 year old male) across idealised whole body irradiation geometries for the major organs (active marrow, colon, lung, stomach wall, and breast) at the energy of 0.1 MeV. Effective dose coefficients were also derived for applicable situations, e.g., radiation protection or risk projection. Our results are the first comprehensive set of organ and effective dose coefficients applicable to children and adolescents based on the newly adopted ICRP pediatric phantom series. Our tabulated organ and effective dose coefficients for these next-generation phantoms should provide more accurate estimates of organ doses in children than earlier dosimetric models allowed. [ABSTRACT FROM AUTHOR]

Aircraft crew members are occupationally exposed to considerable levels of cosmic radiation at flight altitudes. Since aircrew (pilots and passengers) are in the sitting posture for most of the time during flight, and up to now there has been no data on the effective dose rate calculated for aircrew dosimetry in flight altitude using a sitting phantom, we therefore calculated the effective dose rate using a phantom in the sitting and standing postures in order to compare the influence of the posture on the radiation protection of aircrew members. We found that although the better description of the posture in which the aircrews are exposed, the results of the effective dose rate calculated with the phantom in the sitting posture were very similar to the results of the phantom in the standing posture. In fact we observed only a 1% difference. These findings indicate the adequacy of the use of dose conversion coefficients for the phantom in the standing posture in aircrew dosimetry. We also validated our results comparing the effective dose rate obtained using the standing phantom with values reported in the literature. It was observed that the results presented in this study are in good agreement with other authors (the differences are below 30%) who have measured and calculated effective dose rates using different phantoms. [ABSTRACT FROM AUTHOR]

When converting voxel phantoms to a surface format, the small intestine (SI), which is usually not accurately represented in a voxel phantom due to its complex and irregular shape on one hand and the limited voxel resolutions on the other, cannot be directly converted to a high-quality surface model. Currently, stylized pipe models are used instead, but they are strongly influenced by developer’s subjectivity, resulting in unacceptable geometric and dosimetric inconsistencies. In this paper, we propose a new method for the construction of SI models based on the Monte Carlo approach. In the present study, the proposed method was tested by constructing the SI model for the polygon-mesh version of the ICRP reference male phantom currently under development. We believe that the new SI model is anatomically more realistic than the stylized SI models. Furthermore, our simulation results show that the new SI model, for both external and internal photon exposures, leads to dose values that are more similar to those of the original ICRP male voxel phantom than does the previously constructed stylized SI model. [ABSTRACT FROM AUTHOR]

We developed computational methods and tools to assess organ doses for pediatric and adult patients undergoing computed tomography (CT) examinations. We used the International Commission on Radiological Protection (ICRP) reference pediatric and adult phantoms combined with the Monte Carlo simulation of a reference CT scanner to establish comprehensive organ dose coefficients (DC), organ absorbed dose per unit volumetric CT Dose Index (CTDIvol) (mGy/mGy). We also developed methods to estimate organ doses with tube current modulation techniques and size specific dose estimates. A graphical user interface was designed to obtain user input of patient- and scan-specific parameters, and to calculate and display organ doses. A batch calculation routine was also integrated into the program to automatically calculate organ doses for a large number of patients. We entitled the computer program, National Cancer Institute dosimetry system for CT(NCICT). We compared our dose coefficients with those from CT-Expo, and evaluated the performance of our program using CT patient data. Our pediatric DCs show good agreements of organ dose estimation with those from CT-Expo except for thyroid. Our results support that the adult phantom in CT-Expo seems to represent a pediatric individual between 10 and 15 years rather than an adult. The comparison of CTDIvol values between NCICT and dose pages from 10 selected CT scans shows good agreements less than 12% except for two cases (up to 20%). The organ dose comparison between mean and modulated mAs shows that mean mAs-based calculation significantly overestimates dose (up to 2.4-fold) to the organs in close proximity to lungs in chest and chest–abdomen–pelvis scans. Our program provides more realistic anatomy based on the ICRP reference phantoms, higher age resolution, the most up-to-date bone marrow dosimetry, and several convenient features compared to previous tools. The NCICT will be available for research purpose in the near future. [ABSTRACT FROM AUTHOR]

After an incident of radiological dispersal devices (RDD), health care providers will be exposed to the contaminated patients in the extended medical treatments. Assessment of potential radiation dose to the health care providers will be crucial to minimize their health risk. In this study, we compiled a set of conversion coefficients (mSv MBq−1 s−1) to readily estimate the effective dose from the time-integrated activity for the health care providers while they deal with internally contaminated patients at different ages. We selected Co-60, Ir-192, Am-241, Cs-137, and I-131 as the major radionuclides that may be used for RDD. We obtained the age-specific organ burdens after the inhalation of those radionuclides from the Dose and Risk Calculation Software (DCAL) program. A series of hybrid computational phantoms (1-, 5-, 10-, and 15 year-old, and adult males) were implemented in a general purpose Monte Carlo (MC) transport code, MCNPX v 2.7, to simulate an adult male health care provider exposed to contaminated patients at different ages. Two exposure scenarios were taken into account: a health care provider (a) standing at the side of patients lying in bed and (b) sitting face to face with patients. The conversion coefficients overall depended on radionuclides, the age of the patients, and the orientation of the patients. The conversion coefficient was greatest for Co-60 and smallest for Am-241. The dose from the 1 year-old patient phantom was up to three times greater than that from the adult patient phantom. The conversion coefficients were less dependent on the age of the patients in the scenario of a health care provider sitting face to face with patients. The dose conversion coefficients established in this study will be useful to readily estimate the effective dose to the health care providers in RDD events. [ABSTRACT FROM AUTHOR]