Male Phantom Research Articles

Comparison of patient specific dose metrics between chest radiography, tomosynthesis, and CT for adult patients of wide ranging body habitus

Given the radiation concerns inherent to the x-ray modalities, accurately estimating the radiation doses that patients receive during different imaging modalities is crucial. This study estimated organ doses, effective doses, and risk indices for the three clinical chest x-ray imaging techniques (chest radiography, tomosynthesis, and CT) using 59 anatomically variable voxelized phantoms and Monte Carlo simulation methods. A total of 59 computational anthropomorphic male and female extended cardiac-torso (XCAT) adult phantoms were used in this study. Organ doses and effective doses were estimated for a clinical radiography system with the capability of conducting chest radiography and tomosynthesis (Definium 8000, VolumeRAD, GE Healthcare) and a clinical CT system (LightSpeed VCT, GE Healthcare). A Monte Carlo dose simulation program (PENELOPE, version 2006, Universitat de Barcelona, Spain) was used to mimic these two clinical systems. The Duke University (Durham, NC) technique charts were used to determine the clinical techniques for the radiographic modalities. An exponential relationship between CTDIvol and patient diameter was used to determine the absolute dose values for CT. The simulations of the two clinical systems compute organ and tissue doses, which were then used to calculate effective dose and risk index. The calculation of the two dose metrics used the tissue weighting factors from ICRP Publication 103 and BEIR VII report. The average effective dose of the chest posteroanterior examination was found to be 0.04 mSv, which was 1.3% that of the chest CT examination. The average effective dose of the chest tomosynthesis examination was found to be about ten times that of the chest posteroanterior examination and about 12% that of the chest CT examination. With increasing patient average chest diameter, both the effective dose and risk index for CT increased considerably in an exponential fashion, while these two dose metrics only increased slightly for radiographic modalities and for chest tomosynthesis. Effective and organ doses normalized to mAs all illustrated an exponential decrease with increasing patient size. As a surface organ, breast doses had less correlation with body size than that of lungs or liver. Patient body size has a much greater impact on radiation dose of chest CT examinations than chest radiography and tomosynthesis. The size of a patient should be considered when choosing the best thoracic imaging modality.

Development of a 3D human body library based on polygonal mesh surface for whole body counter set-up calibration

A Whole Body Counter (WBC) is a common facility to routinely assess the internal contamination of exposed workers and especially in the case of radiation release accidents. The calibration of the counting device is usually done by using anthropomorphic physical phantoms representing the human body. Due to such a challenge of having representative physical phantoms a virtual calibration has been introduced. The use of computational phantoms and Monte Carlo methods to simulate radiation transport have been demonstrated to be a worthy alternative, not only as a complementary calibration method but also as a powerful tool for the design and optimization of counting geometries. In this study we introduce a methodology for building a 3D human body library that spans variation in both subject shape and size. Open source codes as MakeHuman and Blender software packages have been used for the creation and modelling of 3D humanoid characters based on polygonal mesh surfaces. Also, a home-made software was developed whose main goal is to convert the binary 3D voxel grid into a MCNPX input file. This paper summarizes (1) the development of the MaMP and FeMP - Male and Female Mesh Phantoms, the two first mesh phantoms generated from a series of 3D human bodies library created at SCK-CEN and (2) presents a comparison between the counting efficiency results obtained from the simulations of both mesh phantoms using MCNPX code.

Monte Carlo estimation of radiation dose in organs of female and male adult phantoms due to FDG-F18 absorbed in the lungs

The determination of dose conversion factors (S values) for the radionuclide fluorodeoxyglucose ( 18 F-FDG) absorbed in the lungs during a positron emission tomography (PET) procedure was calculated using the Monte Carlo method (MCNPX version 2.7.0). For the obtained dose conversion factors of interest, it was considered a uniform absorption of radiopharmaceutical by the lung of a healthy adult human. The spectrum of fluorine was introduced in the input data file for the simulation. The simulation took place in two adult phantoms of both sexes, based on polygon mesh surfaces called FASH and MASH with anatomy and posture according to ICRP 89. The S values for the 22 internal organs/tissues, chosen from ICRP No. 110, for the FASH and MASH phantoms were compared with the results obtained from a MIRD V phantoms called ADAM and EVA used by the Committee on Medical Internal Radiation Dose (MIRD). We observed variation of more than 100% in S values due to structural anatomical differences in the internal organs of the MASH and FASH phantoms compared to the mathematical phantom.

Effective dose in percutaneous transhepatic biliary drainage examination using PCXMC2.0 and MCNP5 Monte Carlo codes

ObjectivesTo estimate the organ equivalent doses and the effective doses (E) in patient undergoing percutaneous transhepatic biliary drainage (PTBD) examinations, using the MCNP5 and PCXMC2 Monte Carlo-based codes. MethodsThe purpose of this study is to estimate the organ doses to patients undergoing PTBD examinations by clinical measurements and Monte Carlo simulation. Dose area products (DAP) values were assessed during examination of 43 patients undergoing PTBD examination separated into groups based on the gender and the dimensions and location of the beam. ResultsMonte Carlo simulation of photon transport in male and female mathematical phantoms was applied using the MCNP5 and PCXMC2 codes in order to estimate equivalent organ doses. Regarding the PTBD examination the organ receiving the maximum radiation dose was the lumbar spine. The mean calculated HT for the lumbar spine using the MCNP5 and PCXMC2 methods respectively, was 117.25 mSv and 131.7 mSv, in males. The corresponding doses were 139.45 mSv and 157.1 mSv respectively in females. The HT values for organs receiving considerable amounts of radiation during PTBD examinations were varied between 0.16% and 73.2% for the male group and between 1.10% and 77.6% for the female group. E in females and males using MCNP5 and PCXMC2.0 was 5.88 mSv and 6.77 mSv, and 4.93 mSv and 5.60 mSv. ConclusionThe doses remain high compared to other invasive operations in interventional radiology. There is a reasonable good coincidence between the MCNP5 and PCXMC2.0 calculation for most of the organs.

An internal radiation dosimetry computer program, IDAC 2.0, for estimation of patient doses from radiopharmaceuticals

The internal dosimetry computer program internal dose assessment by computer (IDAC) for calculations of absorbed doses to organs and tissues as well as effective doses to patients from examinations with radiopharmaceuticals has been developed. The new version, IDAC2.0, incorporates the International Commission on Radiation Protection (ICRP)/ICRU computational adult male and female voxel phantoms and decay data from the ICRP publication 107. Instead of only 25 source and target regions, calculation can now be made with 63 source regions to 73 target regions. The major advantage of having the new phantom is that the calculations of the effective doses can be made with the latest tissue weighting factors of ICRP publication 103. IDAC2.0 uses the ICRP human alimentary tract (HAT) model for orally administrated activity and for excretion through the gastrointestinal tract and effective doses have been recalculated for radiopharmaceuticals that are orally administered. The results of the program are consistent with published data using the same specific absorption fractions and also compared with published data from the same computational phantoms but with segmentation of organs leading to another set of specific absorption fractions. The effective dose is recalculated for all the 34 radiopharmaceuticals that are administered orally and has been published by the ICRP. Using the new HAT model, new tissue weighting factors and the new adult computational voxel phantoms lead to an average effective dose of half of its earlier estimated value. The reduction mainly depends on electron transport simulations to walled organs and the transition from the stylised phantom with unrealistic interorgan distances to more realistic voxel phantoms.

Effective dose evaluation for BNCT brain tumor treatment based on voxel phantoms

For BNCT treatments, in addition to tumor target doses, non-negligible doses will result in all the remaining organs of the body. This work aims to evaluate the effective dose as well as the average absorbed doses of each of organs of patients with brain tumor treated in the BNCT epithermal neutron beam at THOR. The effective doses were evaluated according to the definitions of ICRP Publications 60 and 103 for the reference male and female computational phantoms developed in ICRP Publication 110 by using the MCNP5 Monte Carlo code with the THOR-Y09 beam source. The effective dose acquired in this work was compared with the results of our previous work calculated for an adult hermaphrodite mathematical phantom. It was found that the effective dose for the female voxel phantom is larger than that for the male voxel phantom by a factor of 1.2–1.5 and the effective dose for the voxel phantom is larger than that for the mathematical phantom by a factor of 1.3–1.6. For a typical brain tumor BNCT, the effective dose was calculated to be 1.51Sv and the average absorbed dose for eye lenses was 1.07Gy.

Comparison of methods of acquiring attenuation maps for cardiac SPECT in the presence of respiratory motion

BackgroundWe investigated the effect of the respiratory motion on attenuation-corrected (AC) SPECT images for three different SPECT systems, each using a different approach in obtaining attenuation maps: scanning-line sources (SLS) acquired simultaneous with emission; slow cone-beam CT (CBCT) acquired sequentially to emission; and fast helical CT (HCT) acquired sequentially to emission. MethodsA torso phantom filled with 99mTc was used to model a cardiac perfusion study. Stationary baseline acquisitions were followed by the acquisitions with the phantom moving axially using a computer-controlled motion platform to simulate breathing. In addition, HCT acquisitions were made simulating breath-hold at different extents of misalignment between CT and emission. HCT images were also used to simulate the Average-CT method. Acquisitions were repeated with added breast attachments, and the heart insert in two different orientations. Visual comparison was made of AC maps, AC emission slices and polar maps. Quantitative comparisons were made of global uniformity based on the percent fractional standard deviation (%FSD) of the polar map segment values, and the ratio of the segment values in the Anterior and Inferior walls divided by that of the Lateral and Septal walls (AI/LS ratio). ResultsThe AC maps for the SLS were inferior to the CT’s, and most impacted by added large breast attachment. Motion artifacts seen on CBCT slices were minimized in the derived attenuation maps. AC maps obtained from HCT showed inconsistent organ sizes depending on the direction of respiration at the time of acquisition. Both visually and quantitatively CBCT resulted in the best uniformity (up to 3.4 % lower in %FSD) for all the stationary acquisitions, and for the motion acquisition of the female phantom with large breast attachment (up to 4.0 % lower). For the motion acquisition of the male phantoms, HCT resulted in slightly better uniformity (<0.5 % lower) than CBCT. Breath-hold at end-expiration slightly improved (up to 1.1 %) the uniformity over the HCT acquired during regular breathing. Further improvement was achieved with the Average-CT method. For all the systems, phantom respiratory motion reduced the AI/LS ratio compared to when the phantoms were stationary. ConclusionsThe CBCT approach resulted in the best uniformity of the AC emission images. For the female phantom with larger breast attachment, HCT and SLS were truncated at some projection angles introducing artifacts into the AC emission images. The emission image artifacts observed with HCT could be mitigated by performing breath-hold acquisition at end-expiration or Average-CT type acquisitions.

Digital Tomosynthesis: A New Technique for Imaging Nephrolithiasis. Specific Organ Doses and Effective Doses Compared With Renal Stone Protocol Noncontrast Computed Tomography

To determine organ-specific doses (ODs) and effective dose (ED) for digital tomosynthesis (DT) and compare it with our institutional renal stone protocol noncontrast computed tomography (NCCT). A validated anthropomorphic male phantom was placed supine on a digital GE Definium 8000 radiological scanner. Thermoluminescent dosimeters were placed in 256 locations and used to measure OD. A routine DT study was performed consisting of 2 scout images and 1 tomographic sweep in a 14.2-degree arc over the phantom. Software is used to recreate a series of coronal images from the sweep. ODs were determined as the sum of the doses for the study. Equivalent doses were calculated by multiplying OD with the appropriate tissue weighting factor. ED is the summation of the equivalent doses. OD and ED were determined in a similar fashion (using dosimeters) for a renal stone protocol NCCT and doses were compared. ODs for DT are significantly lower compared with NCCT. The ED for NCCT is 3.04 ± 0.34 mSv. The calculated ED for DT is 0.87 ± 0.15 mSv (2 scouts at 0.17 mSv and 0.14 mSv and 1 sweep at 0.56 mSv), P <.0001. DT exposes patients to substantially less radiation than NCCT. This is particularly true for radiation-sensitive organs. Further studies are needed to compare the sensitivity and specificity of DT as compared with NCCT. However, its low overall radiation dose makes it an ideal study for the follow-up of recurrent stone formers in the office setting.

Biodistribution and Radiation Dosimetry of 18F-CP-18, a Potential Apoptosis Imaging Agent, as Determined from PET/CT Scans in Healthy Volunteers

(18)F-CP-18, or (18S,21S,24S,27S,30S)-27-(2-carboxyethyl)-21-(carboxymethyl)-30-((2S,3R,4R,5R,6S)-6-((2-(4-(3-F18-fluoropropyl)-1H-1,2,3-triazol-1-yl)acetamido)methyl)-3,4,5-trihydroxytetrahydro-2H-pyran-2-carboxamido)-24-isopropyl-18-methyl-17,20,23,26,29-pentaoxo-4,7,10,13-tetraoxa-16,19,22,25,28-pentaazadotriacontane-1,32-dioic acid, is being evaluated as a tissue apoptosis marker for PET imaging. The purpose of this study was to determine the biodistribution and estimate the normal-organ radiation-absorbed doses and effective dose from (18)F-CP-18. Successive whole-body PET/CT scans were obtained at approximately 7, 45, 90, 130, and 170 min after intravenous injection of (18)F-CP-18 in 7 healthy human volunteers. Blood samples and urine were collected between the PET/CT scans, and the biostability of (18)F-CP-18 was assessed using high-performance liquid chromatography. The PET scans were analyzed to determine the radiotracer uptake in different organs. OLINDA/EXM software was used to calculate human radiation doses based on the biodistribution of the tracer. (18)F-CP-18 was 54% intact in human blood at 135 min after injection. The tracer cleared rapidly from the blood pool with a half-life of approximately 30 min. Relatively high (18)F-CP-18 uptake was observed in the kidneys and bladder, with diffuse uptake in the liver and heart. The mean standardized uptake values (SUVs) in the bladder, kidneys, heart, and liver at around 50 min after injection were approximately 65, 6, 1.5, and 1.5, respectively. The calculated effective dose was 38 ± 4 μSv/MBq, with the urinary bladder wall having the highest absorbed dose at 536 ± 61 μGy/MBq using a 4.8-h bladder-voiding interval for the male phantom. For a 1-h voiding interval, these doses were reduced to 15 ± 2 μSv/MBq and 142 ± 15 μGy/MBq, respectively. For a typical injected activity of 555 MBq, the effective dose would be 21.1 ± 2.2 mSv for the 4.8-h interval, reduced to 8.3 ± 1.1 mSv for the 1-h interval. (18)F-CP-18 cleared rapidly through the renal system. The urinary bladder wall received the highest radiation dose and was deemed the critical organ. Both the effective dose and the bladder dose can be reduced by frequent voiding. From the radiation dosimetry perspective, the apoptosis imaging agent (18)F-CP-18 is suitable for human use.

A comparative study of space radiation organ doses and associated cancer risks using PHITS and HZETRN

NASA currently uses one-dimensional deterministic transport to generate values of the organ dose equivalent needed to calculate stochastic radiation risk following crew space exposures. In this study, organ absorbed doses and dose equivalents are calculated for 50th percentile male and female astronaut phantoms using both the NASA High Charge and Energy Transport Code to perform one-dimensional deterministic transport and the Particle and Heavy Ion Transport Code System to perform three-dimensional Monte Carlo transport. Two measures of radiation risk, effective dose and risk of exposure-induced death (REID) are calculated using the organ dose equivalents resulting from the two methods of radiation transport. For the space radiation environments and simplified shielding configurations considered, small differences (<8%) in the effective dose and REID are found. However, for the galactic cosmic ray (GCR) boundary condition, compensating errors are observed, indicating that comparisons between the integral measurements of complex radiation environments and code calculations can be misleading. Code-to-code benchmarks allow for the comparison of differential quantities, such as secondary particle differential fluence, to provide insight into differences observed in integral quantities for particular components of the GCR spectrum.

Conversion of ICRP male reference phantom to polygon-surface phantom

The International Commission on Radiological Protection (ICRP) reference phantoms, developed based on computed tomography images of human bodies, provide much more realism of human anatomy than the previously used MIRD5 (Medical Internal Radiation Dose) mathematical phantoms. It has been, however, realized that the ICRP reference phantoms have some critical limitations showing a considerable amount of holes for the skin and wall organs mainly due to the nature of voxels of which the phantoms are made, especially due to their low voxel resolutions. To address this problem, we are planning to develop the polygon-surface version of ICRP reference phantoms by directly converting the ICRP reference phantoms (voxel phantoms) to polygon-surface phantoms. The objective of this preliminary study is to see if it is indeed possible to construct the high-quality polygon-surface phantoms based on the ICRP reference phantoms maintaining identical organ morphology and also to identify any potential issues, and technologies to address these issues, in advance. For this purpose, in the present study, the ICRP reference male phantom was roughly converted to a polygon-surface phantom. Then, the constructed phantom was implemented in Geant4, Monte Carlo particle transport code, for dose calculations, and the calculated dose values were compared with those of the original ICRP reference phantom to see how much the calculated dose values are sensitive to the accuracy of the conversion process. The results of the present study show that it is certainly possible to convert the ICRP reference phantoms to surface phantoms with enough accuracy. In spite of using relatively less resources (<2 man-months), we were able to construct the polygon-surface phantom with the organ masses perfectly matching the ICRP reference values. The analysis of the calculated dose values also implies that the dose values are indeed not very sensitive to the detailed morphology of the organ models in the phantom for highly penetrating radiations such as photons and neutrons. The results of the electron beams, on the other hand, show that the dose values of the polygon-surface phantom are higher by a factor of 2–5 times than those of the ICRP reference phantom for the skin and wall organs which have large holes due to low voxel resolution. The results demonstrate that the ICRP reference phantom could provide significantly unreasonable dose values to thin or wall organs especially for weakly penetrating radiations. Therefore, when compared to the original ICRP reference phantoms, it is believed that the polygon-surface version of ICRP reference phantoms properly developed will not only provide the same or similar dose values (say, difference <5 or 10%) for highly penetrating radiations, but also provide correct dose values for the weakly penetrating radiations such as electrons and other charged particles.

Radiation Exposure in the Follow-Up of Patients with Urolithiasis Comparing Digital Tomosynthesis, Non-Contrast CT, Standard KUB, and IVU

To compare the effective doses (EDs) associated with imaging modalities for follow-up of patients with urolithiasis, including stone protocol non-contrast computed tomography (NCCT), kidney, ureter, and bladder radiograph (KUB), intravenous urogram (IVU), and digital tomosynthesis (DT). A validated Monte-Carlo simulation-based software PCXMC 2.0 (STUK) designed for estimation of patient dose from medical X-ray exposures was used to determine the ED for KUB, IVU (KUB scout plus three tomographic images), and DT (two scouts and one tomographic sweep). Simulations were performed using a two-dimensional stationary field onto the corresponding body area of the built-in digital phantom, with actual kVp, mAs, and geometrical parameters of the protocols. The ED for NCCT was determined using an anthropomorphic male phantom that was placed prone on a 64-slice GE Healthcare volume computed tomography (VCT) scanner. High-sensitivity metal oxide semiconductor field effect transistors dosimeters were placed at 20 organ locations and used to measure organ radiation doses. The ED for a stone protocol NCCT was 3.04±0.34 mSv. The ED for a KUB was 0.63 and 1.1 mSv for the additional tomographic film. The total ED for IVU was 3.93 mSv. The ED for DT performed with two scouts and one sweep (14.2°) was 0.83 mSv. Among the different imaging modalities for follow-up of patients with urolithiasis, DT was associated with the least radiation exposure (0.83 mSv). This ED corresponds to a fifth of NCCT or IVU studies. Further studies are needed to demonstrate the sensitivity and specificity of DT for the follow-up of nephrolithiasis patients.

Evaluation of the use of surrogate tissues for calculating radiation dose to lymphatic nodes from external photon beams.

Lymphatic node chains of the human body are particularly difficult to realistically model in computational human phantoms. In the absence of a lymphatic node model, researchers have used the following surrogate tissues to calculate the radiation dose to the lymphatic nodes: blood vessels, muscle and the combination of the muscle and adipose tissues. In the present work, the authors investigated whether and in which extent the use of different surrogate tissues is appropriate to assess the lymph node dose, using a realistic model of lymphatic nodes that the authors recently reported. Using a Monte Carlo radiation transport method coupled with the adult male hybrid phantom that included the lymph node model, the air kerma-to-absorbed dose conversion coefficients (Gy Gy(-1)) to the lymph nodes and other tissues used as surrogates for external photon beams of 15 discrete energies (0.015-10 MeV) were computed using the following six idealised geometries: anterior-posterior (AP), posterior-anterior (PA), right lateral, left lateral, rotational and isotropic. To validate the results of this study, the lymph node dose calculated here was compared with the dose published by the International Commission on Radiological Protection for the adult male reference phantom. The lymph node dose conversion coefficients with the values calculated for the blood vessels, muscle, adipose tissue and the combination of muscle and adipose tissues were then compared. It was found that muscle was the best estimator for the lymph nodes, with a dose difference averaged across energies >0.08 MeV of <8 % in all irradiation geometries excluding the AP and PA geometries for which the blood vessels were found to be the best estimator. In conclusion, muscle and blood vessels may preferably be used as surrogate tissues in the absence of lymphatic nodes in a given voxel phantom. For energies <0.08 MeV, for which the authors observed a difference of up to 30-fold, an explicit lymph node model may be required to prevent increasing differences with the lymph node dose as the photon energy decreases, though the absolute values of the dose conversion coefficients are smaller than at higher energy.

Organ S values and effective doses for family members exposed to adult patients following I-131 treatment: A Monte Carlo simulation study

To calculate organ S values (mGy∕Bq-s) and effective doses per time-integrated activity (mSv∕Bq-s) for pediatric and adult family members exposed to an adult male or female patient treated with I-131 using a series of hybrid computational phantoms coupled with a Monte Carlo radiation transport technique. A series of pediatric and adult hybrid computational phantoms were employed in the study. Three different exposure scenarios were considered: (1) standing face-to-face exposures between an adult patient and pediatric or adult family phantoms at five different separation distances; (2) an adult female patient holding her newborn child, and (3) a 1-yr-old child standing on the lap of an adult female patient. For the adult patient model, two different thyroid-related diseases were considered: hyperthyroidism and differentiated thyroid cancer (DTC) with corresponding internal distributions of 131I. A general purpose Monte Carlo code, MCNPX v2.7, was used to perform the Monte Carlo radiation transport. The S values show a strong dependency on age and organ location within the family phantoms at short distances. The S values and effective dose per time-integrated activity from the adult female patient phantom are relatively high at shorter distances and to younger family phantoms. At a distance of 1 m, effective doses per time-integrated activity are lower than those values based on the NRC (Nuclear Regulatory Commission) by a factor of 2 for both adult male and female patient phantoms. The S values to target organs from the hyperthyroid-patient source distribution strongly depend on the height of the exposed family phantom, so that their values rapidly decrease with decreasing height of the family phantom. Active marrow of the 10-yr-old phantom shows the highest S values among family phantoms for the DTC-patient source distribution. In the exposure scenario of mother and baby, S values and effective doses per time-integrated activity to the newborn and 1-yr-old phantoms for a hyperthyroid-patient source are higher than values for a DTC-patient source. The authors performed realistic assessments of 131I organ S values and effective dose per time-integrated activity from adult patients treated for hyperthyroidism and DTC to family members. In addition, the authors' studies consider Monte Carlo simulated "mother and baby∕child" exposure scenarios for the first time. Based on these results, the authors reconfirm the strong conservatism underlying the point source method recommended by the US NRC. The authors recommend that various factors such as the type of the patient's disease, the age of family members, and the distance∕posture between the patient and family members must be carefully considered to provide realistic dose estimates for patient-to-family exposures.

Radiation Exposure in Urology: A Genitourinary Catalogue for Diagnostic Imaging

Computerized tomography use increased exponentially in the last 3 decades, and it is commonly used to evaluate many urological conditions. Ionizing radiation exposure from medical imaging is linked to the risk of malignancy. We measured the organ and calculated effective doses of different studies to determine whether the dose-length product method is an accurate estimation of radiation exposure. An anthropomorphic male phantom validated for human organ dosimetry measurements was used to determine radiation doses. High sensitivity metal oxide semiconductor field effect transistor dosimeters were placed at 20 organ locations to measure specific organ doses. For each study the phantom was scanned 3 times using our institutional protocols. Organ doses were measured and effective doses were calculated on dosimetry. Effective doses measured by a metal oxide semiconductor field effect transistor dosimeter were compared to calculated effective doses derived from the dose-length product. The mean±SD effective dose on dosimetry for stone protocol, chest and abdominopelvic computerized tomography, computerized tomography urogram and renal cell carcinoma protocol computerized tomography was 3.04±0.34, 4.34±0.27, 5.19±0.64, 9.73±0.71 and 11.42±0.24 mSv, respectively. The calculated effective dose for these studies Was 3.33, 2.92, 5.84, 9.64 and 10.06 mSv, respectively (p=0.8478). The effective dose varies considerable for different urological computerized tomography studies. Renal stone protocol computerized tomography shows the lowest dose, and computerized tomography urogram and the renal cell carcinoma protocol accumulate the highest effective doses. The calculated effective dose derived from the dose-length product is a reasonable estimate of patient radiation exposure.

MO‐D‐141‐10: Development of 4D XCAT Pediatric Reference Phantoms for Multi‐Modality Imaging Research and Optimization

Purpose: A set of 4D Extended Cardiac‐Torso (XCAT) pediatric reference phantoms were created for multimodality imaging research, which have highly detailed whole‐body anatomies, including cardiac and respiratory functions. Models were created for newborn, 1‐year, 5‐year, 10‐year, and 15‐year old males and females capturing the anatomical variations of childhood development. Methods: The initial anatomy of each phantom was obtained from the Duke University PET‐CT database. The major organs and structures for each phantom were segmented from the corresponding data using semiautomatic and manual segmentation. 3D Non‐Uniform Rational B‐Spline (NURBS) surfaces were fitted to the segmented data. Arms and legs were manually attached using scaled versions of the original XCAT adult male and female phantoms. Some patient datasets had incomplete skulls; skullcaps were manually matched to complete the skulls of these datasets. A multichannel large deformation diffeomorphic metric mapping (MC‐LDDMM) algorithm was used to calculate the transform from a template XCAT phantom to the target patient model, which filled in unsegmented structures within the target phantom and implemented the 4D cardiac and respiratory models in the new anatomy. Organ weights were matched to the 50th percentile ICRP publication 89 values within 5%. Results: A reference set of 10 pediatric phantoms were created with thousands of anatomical structures and cardiac and respiratory motions. These phantoms can be combined with existing simulation packages to simulate realistic imaging data. The phantoms provide a valuable tool to investigate radiation dose and image quality optimization. Conclusion: The development of patient‐derived pediatric computational phantoms is useful in providing variable anatomies for simulation. Future work will expand this 10‐phantom base to a host of pediatric phantoms representative of the public at large. This can provide a means to evaluate and improve pediatric imaging devices and to optimize CT protocols in terms of image quality and radiation dose.

MO‐D‐134‐01: K‐Factors for Overweight and Obese Patients in CT Examinations as a Function of Body Mass Index

Purpose: To generate Dose Length Product to Effective Dose conversion factors (k‐factors) for a series of overweight and obese patients and to establish a functional form for k‐factors in relation to body mass index. Methods: Using the Monte Carlo code MCNPX 2.5.0 and a validated model of the CT source, CT scans were simulated on a series of overweight and obese adult male and female phantoms with fixed height and body mass index (BMI) ranging from 23 to 45. For several CT scan protocols simulations generated the organ doses and effective doses using ICRP 103 tissue weighting factors. The k‐factors were then derived using the dose length product (DLP) for each protocol and the effective dose from pairs of phantoms with the same BMI. For each protocol, a regression analysis was performed for k‐factors to BMI. Results: The calculated k‐factors showed a consistent trend of decreasing with increasing BMI for each of the protocols. In the pelvic scan protocol, for example, the k‐factor for patients with a BMI of 45 is 42% of that for an average sized individual. The k‐factor equations in terms of BMI fit an exponential function regression for all protocols with R‐squared values greater than 0.99 in every case. Conclusion: Where patient height and weight are available, the BMI‐dependent k‐factor equations can provide more accurate effective dose estimation for overweight and obese patients. While they do not provide the patient‐specific dose information that is the purpose of some modern CT dose tracking software, they provide easy access to more appropriate risk estimation and a better metric for performance tracking of a diverse patient population than DLP alone. One member was funded by the 2012‐2013 J. Newell Stannard Fellowship Award from Health Physics Society.

WE‐C‐108‐05: A Hardware Accelerator Based Fast Monte Carlo Code for Radiation Dosimetry: Software Design and Preliminary Results

Purpose: Monte Carlo (MC) simulation provides the most accurate results for CT dose calculations. Yet it is a time‐consuming task which often takes long time to run on CPUs. Using the recently developed hardware accelerators such as Graphics Processing Unit (GPU) and the Intel Xeon Phi coprocessor, one can run the MC simulations in massively parallel and reduce the simulation time significantly. In this work we present our effort of developing a new MC suite, Accelerated Radiation‐transport Computations in Heterogeneous EnviRonments (ARCHER), which utilizes NVIDIA GPUs and other accelerators. Methods: We first developed the radiation transport MC codes in C, and then adapted the code to ARCHERGPU and ARCHERMIC which are specific for NVIDIA GPU and Intel MIC architecture, respectively. Currently the code is capable of calculating the dose for CT X‐ray scan and electron radiotherapy. Our code also incorporated a whole CT scanner model and various computational human phantoms. Results: We tested our GPU‐based MC code on NVIDIA Tesla M2090 GPUs and compared its performance with other MC codes running on an Intel Xeon X5650 CPU. Two tests were carried out: 1) For a whole body helical CT scan with RPI‐Adult male obese phantom and 9e8 incoming photons, the ARCHER_GPU code and ARCHER_MIC code are 1200 and 561 times faster, respectively, than MCNPX running on the CPU. 2) For a simple water‐aluminum‐water phantom and 20MeV electron source, the ARCHER_GPU code takes 186 sec to simulate 6e6 electrons, and it is about 1000 times faster than MCNPX running on the CPU. Conclusion: Our preliminary results showed the efficiency of using different hardware accelerators to speed up MC radiation transport simulations for medical dosimetry. On‐going work includes further optimization of the code and implementation of more complex physics models.

TU‐G‐103‐05: Affordable Supercomputer‐Based Monte Carlo CT Dose Calculations: A Hardware Comparison Between Nvidia M2090 GPU and Intel Xeon Phi 5110p Coprocessor

Purpose: To develop a fast Monte Carlo code ARCHER (a testbed for Accelerated Radiation‐transport Computation in Heterogeneous EnviRonments) to calculate CT imaging organ doses on heterogeneous computing systems. Methods: ARCHER simulates the transport of low‐energy (1∼140keV) photons in heterogeneous media using two selectable interaction models, simple and detailed. It includes an extensive library of voxelized human phantoms such as RPI‐Pregnant women with 3, 6, 9 month gestation, extended RPI‐Adult male and female phantoms representing patients of different obesity level. It contains a validated scanner model based on a GE LightSpeed third‐generation 16‐multi‐detector CT. A series of scan protocols are predefined, including a combination of scan mode (helical or axial), beam collimation (5, 10, or 20 mm) and kVp (80, 100, 120 or 140). ARCHER is targeted for three platforms, CPU (an Intel Xeon X5650 6‐core processor), GPU (Nvidia M2090 GPU), and coprocessor (Intel Xeon Phi 5110p coprocessor), and correspondingly has three code variants developed in MPI‐OpenMP, CUDA and offload OpenMP respectively. Results: Absorbed doses to 28 organs/tissues of dosimetric interest were calculated. MCNPX was used as the accuracy benchmark. The average difference of the organ doses calculated by MCNPX and ARCHER were found to be less than 5% and 0.5% for simple and detailed interaction models respectively, indicating an excellent agreement. While ARCHER's three variants were 63∼1207x faster than MCNPX, the GPU and coprocessor codes were 1.6∼3.4x faster than the CPU (6 core) code. Conclusion: The accelerator‐based new Monte Carlo code ARCHER is developed for accurate and fast CT imaging organ dose calculations. Its full capability to simulate patients of different genders and body sizes receiving different scan protocols exhibits high clinical value.

SU-C-144-04: Whole Body and Relative Organ Dose Values From Neutron and Gamma Irradiation of the Liver and Breast in a Voxelized Anthropomorphic Phantom Using Monte Carlo Methods

Purpose: Using Monte Carlo, we estimated the 3-dimensional organ-dose distribution for neutron and gamma irradiation of the male liver, female liver, and female breasts for neutron-and gamma-stimulated imaging. Understanding the dose distribution from these diagnostic scans is essential for assessing radiation risk. Methods: Monte Carlo was performed using the GEANT4 GATE application and a voxelized XCAT human phantom. Male and female XCAT phantoms were voxelized into 256×256×600 voxels (3.125×3.125×3.125mm^3). A monoenergetic rectangular beam of neutrons or gammas with 1.6×10^7 particles was irradiated onto a 2cm thick slice at eight different angles from 0–180°. For the liver, the beam rotated about the axis of the torso. For the breast, the beam rotated around the pendulous breasts. The neutron irradiation utilized a 5MeV neutron beam and the gamma irradiation utilized a 7MeV gamma beam. Dose volume histograms were computed to analyze the absolute and relative doses in each organ. Results: The neutron irradiation of the liver for both the male/female phantoms imparted the highest organ dose to the liver. All other organ doses were below ∼15% of the liver dose, except for the stomach-wall which registered ∼80% and ∼70% respectively for the male and female. The highest dose for gamma irradiation of the liver occurred in the stomach-wall, with a relative liver dose of ∼70% in the male and ∼75% in the female. Most other organ doses were below ∼10% of the stomach dose. For the breast scans, both the neutron and gamma irradiation registered maximum organ doses in the breasts, with all other relative organ doses being well below 2% of the breast dose. Conclusion: Neutron and gamma irradiation of target organs such as the liver and breasts imparts the maximum dose to the primary target organ and a considerably lower dose to proximal organs outside of the beam plane.