Computed Tomography Scanner Model Research Articles

Inter-Rater Reliability of Hounsfield Units as a Measure of Bone Density: Applications in the Treatment of Thoracolumbar Fractures

The study sought to investigate the reliability of computed tomography (CT)-derived Hounsfield unit (HU) measurements and ascertain the correlation between HU with quantitative CT (qCT)-derived bone mineral density (BMD) in cases of traumatic thoracolumbar fracture, based on native CT scans. This study is a retrospective cross-sectional analysis of data sets from patients who received native CT scans and bone mineral density measurements (qCT) of the same vertebral body. Two different CT scanner models were used. The inter-rater reliability of 4 raters, which measured HU in native CT scans, was calculated using intraclass correlation coefficient for absolute agreement (ICC(3,1)). For the correlation between HU and qCT values, respectively the prediction of qCT based on HU, linear regression was used. Bland-Altman plots were used for visual comparison of predicted and measured qCT values. In total 305 data sets were analyzed. CT scanner model was found to have no significant impact on HU (P= 0.125). The inter-rater reliability for HU measurements from native CT scans was ICC(3,1)=0.932 (95%confidence interval 0.919-0.943, P < 0.001). The linear regression showed significant correlation of HU and qCT values for each rater (P < 0.001). The equation for qCT prediction with averaged coefficient and constant is qCT= 0.8 HU+ 5. In the Bland-Altman plots no bias of predicted qCT values could be found, but a trend to overestimate predicted higher qCT values and underestimate lower qCT values, respectively. HU measurement shows very high inter-rater reliability. The HU values correlate closely with qCT BMD values. In summary, it seems that HU measurement is a suitable tool to readily and accurately assess bone quality without further scans or effort in cases of thoracolumbar spinal trauma.

A Review of Organ Dose Calculation Tools for Patients Undergoing Computed Tomography Scans

Background: Computed tomography (CT) is one of the crucial diagnostic tools in modern medicine. However, careful monitoring of radiation dose for CT patients is essential since the procedure involves ionizing radiation, a known carcinogen.Materials and Methods: The most desirable CT dose descriptor for risk analysis is the organ absorbed dose. A variety of CT organ dose calculators currently available were reviewed in this article.Results and Discussion: Key common elements included in CT dose calculators were discussed and compared, such as computational human phantoms, CT scanner models, organ dose database, effective dose calculation methods, tube current modulation modeling, and user interface platforms.Conclusion: It is envisioned that more research needs to be conducted to more accurately map CT coverage on computational human phantoms, to automatically segment organs and tissues for patient-specific dose calculations, and to accurately estimate radiation dose in the cone beam computed tomography process during image-guided radiation therapy.

Feasibility of the Quantitative Assessment Method for CT Quality Control in Phantom Image Evaluation

Computed tomography (CT) quality control (QC) is regularly performed with standard phantoms, to bar faulty equipment from medical use. Its accuracy may be improved by replacing qualitative methods based on good visual distinction with pixel value-based quantitative methods. We hypothesized that statistical texture analysis (TA) that covers the entire phantom image would be a more appropriate tool. Therefore, our study devised a novel QC method based on the TA for contrast resolution (CR) and spatial resolution (SR) and proposed new, quantitative CT QC criteria. TA of CR and SR images on an American Association of Physicists in Medicine (AAPM) CT Performance Phantom were performed with nine CT scanner models. Six texture descriptors derived from first-order statistics of grayscale image histograms were analyzed. Principal component analysis was used to reveal descriptors with high utility. For CR evaluation, contrast and softness were the most accurate descriptors. For SR evaluation, contrast, softness, and skewness were the most useful descriptors. We propose the following ranges: contrast for CR, 29.5 ± 15%, for SR, 29 ± 10%; softness for CR, &lt;0.015, for SR, &lt;0.014; and skewness for SR, &gt;−1.85. Our novel TA method may improve the assessment of CR and SR of AAPM phantom images.

Quantification and homogenization of image noise between two CT scanner models.

Feedback from radiologists indicated that differences in image appearance and noise impeded reading of post‐contrast computed tomography (CT) scans from an updated CT scanner that was recently added to a fleet of existing scanners from the same vendor, despite using identically named reconstruction algorithms. The goals of this work were to quantify and possibly standardize image quality on the new and an existing scanner using phantom images. Three months of daily quality control images were analyzed to determine the mean CT number and noise magnitude in a water phantom. Next, subtraction images from the uniformity section of an American College of Radiology CT phantom were used to generate noise power spectra for both scanners. Then, a semi‐anthropomorphic liver phantom was imaged with both scanners in triplicate using identical body protocols to quantify differences CT number and noise magnitude. Finally, the scanner dependence of CT number and noise magnitude on material attenuation was quantified using a multi‐energy CT phantom with 15 material inserts. Significant differences between scanners were determined using a paired or Welch's t test as appropriate. In daily quality control images, the new scanner exhibited slightly higher CT number (0.697 vs. 0.412, P < 0.001, n = 85) and slightly lower noise magnitude (4.85 vs. 4.94, P < 0.001, n = 85). Measured NPS was not significantly different between the existing and new scanners. Interestingly, it was observed that the noise magnitude from the new scanner increased with increasing material attenuation in both the liver (P = 0.008) and multi‐energy (P < 0.001) phantoms. Using an alternate reconstruction algorithm with the new scanner eliminated this deviation at high material attenuations. While standard noise evaluation in a water phantom was unable to discern differences between the scanners, more comprehensive testing with higher attenuation materials allowed for the characterization and homogenization of image quality.

Interchangeability between real and three-dimensional simulated lung tumors in computed tomography: an interalgorithm volumetry study.

Using hybrid datasets consisting of patient-derived computed tomography (CT) images with digitally inserted computational tumors, we establish volumetric interchangeability between real and computational lung tumors in CT. Pathologically-confirmed malignancies from 30 thoracic patient cases from the RIDER database were modeled. Tumors were either isolated or attached to lung structures. Patient images were acquired on one of two CT scanner models (Lightspeed 16 or VCT; GE Healthcare) using standard chest protocol. Real tumors were segmented and used to inform the size and shape of simulated tumors. Simulated tumors developed in Duke Lesion Tool (Duke University) were inserted using a validated image-domain insertion program. Four readers performed volume measurements using three commercial segmentation tools. We compared the volume estimation performance of segmentation tools between real tumors in actual patient CT images and corresponding simulated tumors virtually inserted into the same patient images (i.e., hybrid datasets). Comparisons involved (1)direct assessment of measured volumes and the standard deviation between simulated and real tumors across readers and tools, respectively, (2)multivariate analysis, involving segmentation tools, readers, tumor shape, and attachment, and (3)effect of local tumor environment on volume measurement. Volume comparison showed consistent trends (9% volumetric difference) between real and simulated tumors across all segmentation tools, readers, shapes, and attachments. Across all cases, readers, and segmentation tools, an intraclass correlation coefficient = 0.99 indicates that simulated tumors correlated strongly with real tumors ( ). In addition, the impact of the local tumor environment on tumor volume measurement was found to have a segmentation tool-related influence. Strong agreement between simulated tumors modeled in this study compared to their real counterparts suggests a high degree of similarity. This indicates that, volumetrically, simulated tumors embedded into patient CT data can serve as reasonable surrogates to real patient data.

P049] Moving forward to personalized pediatric dosimetry on computed tomography applications

Purpose Personalized dosimetry is of high interest in pediatric applications where exposure to ionizing radiation is widely debated. This study intends to create an organ dose database for pediatric reference individuals undergoing computed tomography (CT) examinations. The data will permit quick estimates of organ effective doses for patients of different age, gender, and examination procedure. Methods The GATE MC toolkit [1] was used for modeling a multislice helical CT system. The energy spectrum was calculated using Spektr software, and consequently imported in GATE as a gamma-particle point source with an almost continuous helical movement. To validate our results, simulations were performed with the standard CTDI head/body phantoms. A thin-walled ionization chamber was simulated according to the manufacturer specifications at 1 center, and 4 peripheral positions. Five pediatric computational models in the 5–15 y age-range [2] , [3] , were used to simulate realistic helical chest protocols and compare the variations on absorbed dose/organ. Results The CT scanner model was validated against experimental CTDI measurements with differences being lower than ∼18%. The simulated dose variations for the different pediatric phantoms are presented. Indicatively, normalized absorbed doses for selected organs inside the scan coverage varied between 25–35%, and 43–51% for 5 vs. 8, and 8 vs. 11 years-old girls respectively. Conclusions This is an ongoing study for the creation of a CT dosimetry pediatric database and for the quantification of the differences on the absorbed doses in tissue/organ level, using several models with variations in anatomical features. Every patient could be matched to the best anatomical model of this database (according to characteristics such as weight, height, age, gender) to provide more accurate and patient-specific organ doses.

Phantomless calibration of CT scans for measurement of BMD and bone strength—Inter-operator reanalysis precision

Patient-specific phantomless calibration of computed tomography (CT) scans has the potential to simplify and expand the use of pre-existing clinical CT for quantitative bone densitometry and bone strength analysis for diagnostic and monitoring purposes. In this study, we quantified the inter-operator reanalysis precision errors for a novel implementation of patient-specific phantomless calibration, using air and either aortic blood or hip adipose tissue as internal calibrating reference materials, and sought to confirm the equivalence between phantomless and (traditional) phantom-based measurements. CT scans of the spine and hip for 25 women and 15 men (mean±SD age of 67±9years, range 41–86years), one scan per anatomic site per patient, were analyzed independently by two analysts using the VirtuOst software (O.N. Diagnostics, Berkeley, CA). The scans were acquired at 120kVp, with a slice thickness/increment of 3mm or less, on nine different CT scanner models across 24 different scanners. The main parameters assessed were areal bone mineral density (BMD) at the hip (total hip and femoral neck), trabecular volumetric BMD at the spine, and vertebral and femoral strength by finite element analysis; other volumetric BMD measures were also assessed. We found that the reanalysis precision errors for all phantomless measurements were ≤0.5%, which was as good as for phantom calibration. Regression analysis indicated equivalence of the phantom- versus phantomless-calibrated measurements (slope not different than unity, R2≥0.98). Of the main parameters assessed, non-significant paired mean differences (n=40) between the two measurements ranged from 0.6% for hip areal BMD to 1.1% for mid-vertebral trabecular BMD. These results indicate that phantom-equivalent measurements of both BMD and finite element-derived bone strength can be reliably obtained from CT scans using patient-specific phantomless calibration.

CT dose equilibration and energy absorption in polyethylene cylinders with diameters from 6 to 55 cm

ICRU Report No. 87 Committee and AAPM Task Group 200 designed a three-sectional polyethylene phantom of 30 cm in diameter and 60 cm in length for evaluating the midpoint dose DL(0) and its rise-to-the-equilibrium curve H(L) = DL(0)/D(eq) from computed tomography (CT) scanning, where D(eq) is the equilibrium dose. To aid the use of the phantom in radiation dose assessment and to gain an understanding of dose equilibration and energy absorption in polyethylene, the authors evaluated the short (20 cm) to long (60 cm) phantom dose ratio with a polyethylene diameter of 30 cm, assessed H(L) in polyethylene cylinders of 6-55 cm in diameters, and examined energy absorption in these cylinders. A GEANT4-based Monte Carlo program was used to simulate the single axial scans of polyethylene cylinders (diameters 6-55 cm and length 90 cm, as well as diameter 30 cm and lengths 20 and 60 cm) on a clinical CT scanner (Somatom Definition dual source CT, Siemens Healthcare). Axial dose distributions were computed on the phantom central and peripheral axes. An average dose over the central 23 or 100 mm region was evaluated for modeling dose measurement using a 0.6 cm(3) thimble chamber or a 10 cm long pencil ion chamber, respectively. The short (20 cm) to long (90 cm) phantom dose ratios were calculated for the 30 cm diameter polyethylene phantoms scanned at four tube voltages (80-140 kV) and a range of beam apertures (1-25 cm). H(L) was evaluated using the dose integrals computed with the 90 cm long phantoms. The resultant H(L) data were subsequently used to compute the fraction of the total energy absorbed inside or outside the scan range (E(in)/E or E(out)/E) on the phantom central and peripheral axes, where E = LD(eq) was the total energy absorbed along the z axis. The midpoint dose in the 60 cm long polyethylene phantom was equal to that in the 90 cm long polyethylene phantom. The short-to-long phantom dose ratios changed with beam aperture and phantom axis but were insensitive to tube voltage. H(L) was insensitive to tube voltage and CT scanner model. As phantom diameter increased from 6 to 55 cm, E(in)/E generally decreased but asymptotically approached constant levels on the peripheral axes of large phantoms. The curve of E(in)/E versus scan length was almost identical to that of H(L). Similarly, E(out)/E increased with scan length and asymptotically approached the equilibrium for large scan lengths. E(out)/D(eq) was much less than the equilibrium length L(eq) where H(L) = 0.98, even with scan lengths much larger than L(eq). The polyethylene phantom designed by ICRU Report No. 87 Committee and AAPM Task Group 200 is adequately long for assessing the midpoint dose and its equilibration in CT scanning. The short-to-long phantom dose ratios and the H(L) data provided in this paper allow easy evaluations of the midpoint dose, longitudinal dose distribution, and energy absorption in polyethylene phantoms. The results of dose equilibration and energy absorption presented herein may be insightful for the clinical CT scans with various subject sizes and scan lengths.

Visual scoring of coronary artery calcification in lung cancer screening computed tomography: association with all-cause and cardiovascular mortality risk.

Current and former smokers are at an increased risk for lung cancer and cardiovascular disease (CVD). We investigated two methods of visual scoring of coronary artery calcium on lung cancer screening computed tomography (CT) to predict cardiovascular and all-cause mortality. Cases were 1000 participants, age 55-74 years, enrolled in the National Lung Screening Trial CT arm who died during the study. An equal number of participants alive at the end of the study (controls) were matched in terms of sex, CT scanner vendor, and model, and 5-year age and smoking pack-years group. Coronary calcium was measured visually by three readers using two semiquantitative scoring schemes. Conditional logistic regression was used to analyze the association between the presence and the extent of coronary calcium and all-cause and cardiovascular mortality, stratified on matching criteria. Cases and controls were well matched for age (64±6 vs. 64±5, P=0.95) and mean pack-years smoking (61±24 vs. 62±24, P=1.0). Cases were significantly more likely to have coronary calcium than controls (85 vs. 77%, P<0.001). Having any calcium was associated with an increased risk for CVD mortality using either visual scoring method (odds ratio 3.4, 95% confidence interval 2.0-5.6, P<0.001, and odds ratio 3.3, 95% confidence interval 2.0-5.6, P<0.001). Visual scoring of coronary calcium predicts all-cause and CVD mortality in National Lung Screening Trial participants, independent of current versus former smoking status. Visual coronary calcium scoring in low-dose CT scans helps identify individuals at high risk for mortality who may benefit from further CVD prevention.

The profound effects of patient arm positioning on organ doses from CT procedures calculated using Monte Carlo simulations and deformable phantoms.

The purpose of this study was to evaluate the organ dose differences caused by the arms-raised and arms-lowered postures for multidetector computed tomography procedures. Organ doses were calculated using computational phantoms and Monte Carlo simulations. The arm position in two previously developed adult male and female human phantoms was adjusted to represent 'raised' and 'lowered' postures using advanced BREP-based mesh surface geometries. Organ doses from routine computed tomography (CT) scan protocols, including the chest, abdomen-pelvis, and chest-abdomen-pelvis scans, were simulated at various tube voltages and reported in the unit of mGy per 100 mAs. The CT scanner model was based on previously tested work. The differences in organ dose per unit tube current between raised and lowered arm postures were studied. Furthermore, the differences due to the tube current modulation (TCM) for these two different postures and their impact on organ doses were also investigated. For a given scan parameter, a patient having lowered arms received smaller doses to organs located within the chest, abdomen or pelvis when compared with the patient having raised arms. As expected, this is caused by the attenuation of the primary X rays by the arms. However, the skin doses and bone surface doses in the patient having lowered arms were found to be 3.97-32.12% larger than those in a patient having raised arms due to the fact that more skin and spongiosa were covered in the scan range when the arms are lowered. This study also found that dose differences become smaller with the increase in tube voltage for most of organs or tissues except the skin. For example, the liver dose differences decreased from -15.01 to -11.33% whereas the skin dose differences increased from 21.53 to 25.24% with tube voltage increased from 80 to 140 kVp. With TCM applied, the organ doses of all the listed organs in patient having lowered arms are larger due to the additional tube current necessary to overcome the presence of the arms while maintaining sufficient image quality Arm position affects the dose to internal organs from CT scans by as much as 25.3%. The presence of arms in the scan range results in a dose increase for the skin and bone surface, but a dose decrease for organs located in the torso. Considering the use of TCM, which is common in many clinics, the patient having lowered arms may receive 50% higher radiation dose to most of the organs because of the increased tube current. The use of higher tube voltage might narrow such dose differences between patients of these two postures due to the greater penetration of higher-energy X rays. Therefore, when calculating or reporting patient doses from CT scans, it is prudent to select an appropriate phantom that accurately represents the patient posture.

Direct action of radiation on mummified cells: modeling of computed tomography by Monte Carlo algorithms

X-ray imaging is a nondestructive and preferred method in paleopathology to reconstruct the history of ancient diseases. Sophisticated imaging technologies such as computed tomography (CT) have become common for the investigation of skeletal disorders in human remains. Researchers have investigated the impact of ionizing radiation on living cells, but never on ancient cells in dry tissue. The effects of CT exposure on ancient cells have not been examined in the past and may be important for subsequent genetic analysis. To remedy this shortcoming, we developed different Monte Carlo models to simulate X-ray irradiation on ancient cells. Effects of mummification were considered by using two sizes of cells and three different phantom tissues, which enclosed the investigated cell cluster. This cluster was positioned at the isocenter of a CT scanner model, where the cell hit probabilities P(0,1,…, n) were calculated according to the Poisson distribution. To study the impact of the dominant physics process, CT scans for X-ray spectra of 80 and 120 kVp were simulated. Comparison between normal and dry tissue phantoms revealed that the probability of unaffected cells increased by 21% following cell shrinkage for 80 kVp, while for 120 kVp, a further increase of unaffected cells of 23% was observed. Consequently, cell shrinkage caused by dehydration decreased the impact of X-ray radiation on mummified cells significantly. Moreover, backscattered electrons in cortical bone protected deeper-lying ancient cells from radiation damage at 80 kVp X-rays.

Measurement of Phantomless Thoracic Bone Mineral Density on Coronary Artery Calcium CT Scans Acquired with Various CT Scanner Models

To determine the accuracy and precision of thoracic phantomless bone mineral density (BMD) measurements obtained on coronary artery calcium (CAC) computed tomography (CT) scans by using a variety of commercially available CT scanners. The institutional review board approved this Health Insurance Portability and Accountability Act-compliant study. A total of 4126 asymptomatic subjects (2022 [49%] men, 2104 [51%] women; mean age, 63.7 years ± 11.8 [standard deviation]) underwent CAC CT with the use of a quantitative CT calibration phantom for evaluation of subclinical atherosclerosis. Two hundred eighty subjects also underwent CT of the chest, abdomen, and pelvis (C7 through L5). Mean BMD of three consecutive thoracic vertebrae (in the T7-T10 range) was measured in all 4126 subjects. Individual calibration factors for each phantom insert and a general calibration factor for the spine were determined for each CT scanner model. The study population was then divided into three subgroups: All calibration factors were generated from group 1 (n = 1536) and were applied and tested in group 2 (n = 1587), and effects of various image acquisition parameters were assessed in group 3 (n = 1003). Accuracy (bias) and precision of thoracic phantomless BMD measurements across 14 CT scanner models from five manufacturers were determined. Phantomless BMD values correlated highly with standard phantom-based quantitative CT BMD values (r = 0.987, P < .001). Bias was 3.9% ± 1.4 for phantomless BMD measurements, and the mean coefficient of variation for the general calibration factor was 4.9% ± 2.4. Phantomless BMD can be measured accurately on CAC CT scans acquired with a variety of CT scanners without additional radiation exposure.

Reference standard and statistical model for intersite and temporal comparisons of CT attenuation in a multicenter quantitative lung study

The purpose of this study was to detect and analyze anomalies between a large number of computed tomography (CT) scanners, tracked over time, utilized to collect human pulmonary CT data for a national multicenter study: chronic obstructive pulmonary disease genetic epidemiology study (COPDGene). A custom designed CT reference standard "Test Object" has been developed to evaluate the relevant differences in CT attenuation between CT scanners in COPDGene. The materials used in the Test Object to assess CT scanner accuracy and precision included lung equivalent foam (-856 HU), internal air (-1000 HU), water (0 HU), and acrylic (120 HU). Nineteen examples of the Test Object were manufactured. Initially, all Test Objects were scanned on the same CT scanner before the Test Objects were sent to the 20 specific sites and 42 individual CT scanners that were used in the study. The Test Objects were scanned over 17 months while the COPDGene study continued to recruit subjects. A mixed linear effect statistical analysis of the CT scans on the 19 Test Objects was performed. The statistical model reflected influence of reconstruction kernels, tube current, individual Test Objects, CT scanner models, and temporal consistency on CT attenuation. Depending on the Test Object material, there were significant differences between reconstruction kernels, tube current, individual Test Objects, CT scanner models, and temporal consistency. The two Test Object materials of most interest were lung equivalent foam and internal air. With lung equivalent foam, there were significant (p < 0.05) differences between the Siemens B31 (-856.6, ±0.82; mean ± SE) and the GE Standard (-856.6 ± 0.83) reconstruction kernel relative to the Siemens B35 reference standard (-852.5 ± 1.4). Comparing lung equivalent foam attenuation there were also significant differences between CT scanner models (p < 0.01), tube current (p < 0.005), and in temporal consistency (p < 0.005) at individual sites. However, there were no significant effects measurable using different examples of the Test Objects at the various sites compared to the reference scans of the 19 Test Objects. For internal air, significant (p < 0.005) differences were found between all reconstruction kernels (Siemens B31, GE Standard, and Phillips B) compared to the reference standard. There were significant differences between CT models (p < 0.005), and tube current (p < 0.005). There were no significant effects measurable using different examples of the Test Objects at the various sites compared to the reference scans of the 19 Test Objects. Differences, across scanners, between external air and internal air measures in this simple (relative to the in vivo lung) test object varied by as much as 15 HU. The authors conclude that the Test Object designed for this study was able to detect significant effects regarding individual CT scanners that altered the CT attenuation measurements relevant to the study that are used to determine lung density. Through an understanding of individual scanners, the Test Object analysis can be used to detect anomalies in an individual CT scanner and to statistically model out scanner differences and individual scanner changes over time in a large multicenter trial.

TU‐G‐217BCD‐04: Automated Organ Dose Calculation for Thousands of Computed Tomography Scans

Purpose: To develop and demonstrate an automated computational method used to provide organ and effective dose assessments of computed tomography (CT) examinations, using a pre‐calculated organ dose database. Methods: A five dimensional organ dose matrix, D (33 organs, 6 age groups, 2 genders, 3 tube potentials, scan positions with 1 cm z‐resolution), was calculated using a Monte Carlo transport method which couples a reference CT scanner model (Siemens Sensation 16) with a series of pediatric and adult hybrid computational phantoms. CT scans with a given scan range were approximated as the sum of doses from multiple axial slices included in the scan range of interest. Patient‐specific doses were calculated using the organ and effective doses normalized to CTDIvol of the reference scanner and patient/scan‐specific parameters: body part scanned, CTDIvol, age, gender, scan length, kVp, and mAs. The parameters were obtained from a manually‐ and electronically‐extracted DICOM dataset of 3,982 CT exams randomly selected from five health care systems participating in the NCI‐funded Cancer Research Network (CRN). Illustrative dose analysis and comparison of dose for a subset of scans were performed. Results: Based on an evaluation of 3,983 CT examinations the following values were provided: effective dose, CTDIvol, dose length product (DLP) and the absorbed doses for 33 organs. Illustrative analysis for brain dose in head scans revealed a large dose variation in the age less than 30‐year scans (COV=0.445) compared to the age above 30‐year (COV=0.104). We observed that brain dose is strongly correlated with scan length compared to other scan parameters. Conclusion: The automated organ and effective dose calculation method developed in this study reduces the time needed to calculate doses on a large number of patients. We have successfully utilized this program for a variety of CT‐related studies including retrospective epidemiological study and CT dose trend analysis studies.

WE‐A‐218‐01: NCICT a Computer Program for Organ and Effective Dose Calculation for Pediatric and Adult Patients Undergoing Computed Tomography

Purpose: To develop a computer program for users to conveniently assess organ and effective doses for patients undergoing computed tomography (CT) examinations by using patient‐ and scan‐specific parameters. Methods: A comprehensive organ and effective dose database previously published by the authors was employed in this study. A series of pediatric and adult hybrid computational phantoms representing the International Commission on Radiological Protection (ICRP) reference data was coupled with a reference CT scanner model within Monte Carlo transport code to establish a set of five dimensional dose matrix, D (33 organs, 6 age groups, 2 genders, 3 tube potentials, scan positions with 1 cm z‐resolution). A graphical user interface (GUI) was designed using Visual Basic computer language to obtain user input (patient age and gender, scanner manufacturer and models, head/body filter, pitch, tube potential, tube current, a single rotation time, and scan start and end position). The GUI was then coupled with the dose matrix and a dose calculation routine was written. Organ doses were compared with the values obtained from previous CT dosimetry tools. Results: A computer program, named NCICT, was developed using pre‐ calculated dose matrix. As a result, a total of 33 organ doses and two effective doses based on ICRP Publication 60 and 103 are displayed. Major organ doses were calculated for head, chest, and abdomen‐pelvis scans and compared with the values from CT‐Expo and CTDosimetry. The comparison revealed that use of phantoms with realistic anatomy is crucial to improved accuracy in CT organ dosimetry. Conclusion: NCICT, a user‐ friendly computer program for CT dose calculation was developed and validated. The program provides more realistic patient anatomy, higher age resolution, advanced skeleton dosimetry, and several convenient features compared to the previous tools. The NCICT is under beta testing and will be available for research purpose in the near future.

Organ doses for reference pediatric and adolescent patients undergoing computed tomography estimated by Monte Carlo simulation

To establish an organ dose database for pediatric and adolescent reference individuals undergoing computed tomography (CT) examinations by using Monte Carlo simulation. The data will permit rapid estimates of organ and effective doses for patients of different age, gender, examination type, and CT scanner model. The Monte Carlo simulation model of a Siemens Sensation 16 CT scanner previously published was employed as a base CT scanner model. A set of absorbed doses for 33 organs∕tissues normalized to the product of 100 mAs and CTDI(vol) (mGy∕100 mAs mGy) was established by coupling the CT scanner model with age-dependent reference pediatric hybrid phantoms. A series of single axial scans from the top of head to the feet of the phantoms was performed at a slice thickness of 10 mm, and at tube potentials of 80, 100, and 120 kVp. Using the established CTDI(vol)- and 100 mAs-normalized dose matrix, organ doses for different pediatric phantoms undergoing head, chest, abdomen-pelvis, and chest-abdomen-pelvis (CAP) scans with the Siemens Sensation 16 scanner were estimated and analyzed. The results were then compared with the values obtained from three independent published methods: CT-Expo software, organ dose for abdominal CT scan derived empirically from patient abdominal circumference, and effective dose per dose-length product (DLP). Organ and effective doses were calculated and normalized to 100 mAs and CTDI(vol) for different CT examinations. At the same technical setting, dose to the organs, which were entirely included in the CT beam coverage, were higher by from 40 to 80% for newborn phantoms compared to those of 15-year phantoms. An increase of tube potential from 80 to 120 kVp resulted in 2.5-2.9-fold greater brain dose for head scans. The results from this study were compared with three different published studies and∕or techniques. First, organ doses were compared to those given by CT-Expo which revealed dose differences up to several-fold when organs were partially included in the scan coverage. Second, selected organ doses from our calculations agreed to within 20% of values derived from empirical formulae based upon measured patient abdominal circumference. Third, the existing DLP-to-effective dose conversion coefficients tended to be smaller than values given in the present study for all examinations except head scans. A comprehensive organ∕effective dose database was established to readily calculate doses for given patients undergoing different CT examinations. The comparisons of our results with the existing studies highlight that use of hybrid phantoms with realistic anatomy is important to improve the accuracy of CT organ dosimetry. The comprehensive pediatric dose data developed here are the first organ-specific pediatric CT scan database based on the realistic pediatric hybrid phantoms which are compliant with the reference data from the International Commission on Radiological Protection (ICRP). The organ dose database is being coupled with an adult organ dose database recently published as part of the development of a user-friendly computer program enabling rapid estimates of organ and effective dose doses for patients of any age, gender, examination types, and CT scanner model.

Development of a web-based CT dose calculator: WAZA-ARI

A web-based computed tomography (CT) dose calculation system (WAZA-ARI) is being developed based on the modern techniques for the radiation transport simulation and for software implementation. Dose coefficients were calculated in a voxel-type Japanese adult male phantom (JM phantom), using the Particle and Heavy Ion Transport code System. In the Monte Carlo simulation, the phantom was irradiated with a 5-mm-thick, fan-shaped photon beam rotating in a plane normal to the body axis. The dose coefficients were integrated into the system, which runs as Java servlets within Apache Tomcat. Output of WAZA-ARI for GE LightSpeed 16 was compared with the dose values calculated similarly using MIRD and ICRP Adult Male phantoms. There are some differences due to the phantom configuration, demonstrating the significance of the dose calculation with appropriate phantoms. While the dose coefficients are currently available only for limited CT scanner models and scanning options, WAZA-ARI will be a useful tool in clinical practice when development is finalised.

TH-E-211-02: Estimation of Organ Doses in Reference Pediatric Individuals Undergoing Computed Tomography Using Monte Carlo Simulations

Purpose: To establish an organ dose database for pediatric reference individuals undergoing computed tomography (CT) examinations by using Monte Carlo simulations to readily provide organ doses for patients with different age, gender, examination type, and CT scanner models. Methods and Materials: The Monte Carlo simulation model of Siemens Sensation 16 CT scanner we recently published was employed as base CT scanner model. The CT scanner model was coupled with a series of pediatric hybrid phantoms within MCNPX2.6. Organ doses from helical scans were approximated by the summation of doses from multiple axial slices included in the given scan range of interest which provided flexibility to the CT scan dosimetry calculations. Organ dose calculations were performed for a single axial scan which started from the top of head down to the bottom of the phantoms with an interval of 10 mm for a total of 10 pediatric phantoms: newborn, 1-year, 5-year, 10-year, and 15-year males and females. Results: Absorbed doses (mGy/100mAs-mGy) normalized to 100 mAs and CTDIvol (mGy) were calculated for a total of 30 organs and tissues including active marrow under the tube potentials of 80, 100, and 120 kVp. The normalized organ doses for head, chest, and abdomen/pelvis scans were calculated and compared with the values from CT-Expo. Organ doses based on the hybrid phantom series in this study overall agreed with those from CT-Expo based on two voxel phantoms. Significant dose differences caused by the unrealistic organ locations which were observed for the adult stylized phantoms in the recently published study were not observed. Conclusion: The organ dose matrix established for pediatric individuals will be coupled with the adult version which was recently published and be incorporated into a graphical user interface to provide user-friendly computer program for CT organ dose estimations.

Organ doses for reference adult male and female undergoing computed tomography estimated by Monte Carlo simulations

To develop a computed tomography (CT) organ dose estimation method designed to readily provide organ doses in a reference adult male and female for different scan ranges to investigate the degree to which existing commercial programs can reasonably match organ doses defined in these more anatomically realistic adult hybrid phantoms The x-ray fan beam in the SOMATOM Sensation 16 multidetector CT scanner was simulated within the Monte Carlo radiation transport code MCNPX2.6. The simulated CT scanner model was validated through comparison with experimentally measured lateral free-in-air dose profiles and computed tomography dose index (CTDI) values. The reference adult male and female hybrid phantoms were coupled with the established CT scanner model following arm removal to simulate clinical head and other body region scans. A set of organ dose matrices were calculated for a series of consecutive axial scans ranging from the top of the head to the bottom of the phantoms with a beam thickness of 10 mm and the tube potentials of 80, 100, and 120 kVp. The organ doses for head, chest, and abdomen/pelvis examinations were calculated based on the organ dose matrices and compared to those obtained from two commercial programs, CT-EXPO and CTDOSIMETRY. Organ dose calculations were repeated for an adult stylized phantom by using the same simulation method used for the adult hybrid phantom. Comparisons of both lateral free-in-air dose profiles and CTDI values through experimental measurement with the Monte Carlo simulations showed good agreement to within 9%. Organ doses for head, chest, and abdomen/pelvis scans reported in the commercial programs exceeded those from the Monte Carlo calculations in both the hybrid and stylized phantoms in this study, sometimes by orders of magnitude. The organ dose estimation method and dose matrices established in this study readily provides organ doses for a reference adult male and female for different CT scan ranges and technical parameters. Organ doses from existing commercial programs do not reasonably match organ doses calculated for the hybrid phantoms due to differences in phantom anatomy, as well as differences in organ dose scaling parameters. The organ dose matrices developed in this study will be extended to cover different technical parameters, CT scanner models, and various age groups.

SU-EE-A4-04: Organ Doses in the Reference Adult Male and Female Exposed to Computed Tomography Examinations: Monte Carlo Simulations and Experimental Validation

Purpose: To establish an organ dose database for adult male and female reference individuals undergoing computed tomography(CT) examinations by using the Monte Carlo(MC) method. Methods and Materials: We are using the MC method to estimate organ doses from CT examinations to support epidemiologic studies of the risk of second cancers associated with radiation exposure from CT examination. The fan‐shaped x‐ray beam of a SOMATOM Sensation 16 CT scanner was simulated by using a general purpose MC code, MCNPX v2.6. The bowtie filter was approximated based on beam profile measurements under service mode tube settings. To simulate the anatomy of patients, the University of Florida family of hybrid computational phantoms representing the adult male and female at their 50th percentile body weight and standing height were coupled with the CT scanner model. The reliability of the MC simulation system has been validated by comparing results with measurements from Computed Tomography Dose Index(CTDI) head and body phantoms. Organ absorbed doses were calculated for Head, Chest, Abdomen, and Pelvis examinations and compared with those from two commercial CT dose calculation programs (CT‐expo and CT‐Dosimetry). Results: Central and peripheral doses from the measurements using head and body CTDI phantoms were compared with those from MC simulation. The simulated doses showed good agreement with measured values with the largest percent difference of 8%. Normalized values of organ absorbed dose (mGy/100 mAs) were calculated for 25 organs in the adult male and female phantoms undergoing CT examinations. The dose results were compared with those from the commercial programs, and significant differences up to 200% were shown in major organs.Conclusion: The organ dose database developed in this study significantly improves the accuracy of organ dose assessments in CT examinations which have not been implemented in existing commercial CT dose evaluation programs.