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Title: Energy imparted-based estimates of the effect of z overscanning on adult and pediatric patient effective doses from multi-slice computed tomography

Abstract

In the present study effective dose values normalized to computed tomography dose index measured free in air were calculated for adult, newborn, 1, 5, 10 and 15 year old patients regarding scans of the head, chest, abdomen, pelvis, abdomen and pelvis, and trunk, using the energy imparted method. The effect of z overscanning on patient doses was accounted for, and normalized doses are provided for varying beam collimation, pitch and reconstruction slice width values. The contribution of overscanning depends on patient age, anatomic region imaged, acquisition and reconstruction settings. For a head scan it constitutes 15% of the adult effective dose and 24% of the effective dose to a newborn but for an abdomen scan it may be as high as 58% for a newborn and 31% for an adult. The ratios of normalized pediatric doses relative to that for adults for helical scans depend not only on age but also on acquisition and reconstruction parameters, because of variations in the relative distance between the primary beam and the radiosensitive tissues/organs of the body. Regarding scans of the trunk, pediatric doses are up to a factor of 2.5 times higher compared to adult doses (abdominal scans), whereas for scans ofmore » the head up to a factor of 1.5. Increasing the pitch value of helical scans while maintaining the same effective mAs setting, and hence noise levels, leads to an increase in patient doses which depends on age, body region, scan and reconstruction parameters. The % difference between doses at pitch 1.5 and pitch 1 is more pronounced in the abdominal region (14% increase for adults) and in young patients (31% in a newborn and 18% in a 10 year old patient) and it is minimal in head scans (4% increase in newborns and 1% in adults). If multiple body regions are to be imaged, doses to adults can be reduced by up to 15% and 36% to children by performing single long-range scans. Scanning adult patients at 100 kVp instead of 120 kVp, results in a 32% reduction in effective dose from head scans and 38% for scans of the torso. The corresponding reduction for a 5 year old patient is 31% for the head and 37% for the trunk. Due to the combined overbeaming and overscanning effect the 24 mm collimation is more dose effective in the head mode and the 12 mm collimation in the body mode. Provided data enable informed design of examination protocols, calculation of effective dose values and familiarization with the technical features of multi-detector technology.« less

Authors:
; ; ;  [1];  [2];  [2]
  1. Department of Medical Physics, Faculty of Medicine, University of Crete, P.O. Box 2208, Iraklion 71003, Crete (Greece) and Department of Natural Sciences, Technological Education Institute of Crete, P.O. Box 140, Iraklion 71004, Crete (Greece)
  2. (Greece)
Publication Date:
OSTI Identifier:
20951135
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 4; Other Information: DOI: 10.1118/1.2436980; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ABDOMEN; CHEST; COMPUTERIZED TOMOGRAPHY; DESIGN; DOSIMETRY; HEAD; IMAGE PROCESSING; NOISE; ORGANS; PATIENTS; PEDIATRICS; PELVIS; RADIATION DOSES

Citation Formats

Theocharopoulos, Nicholas, Damilakis, John, Perisinakis, Kostas, Gourtsoyiannis, Nicholas, Department of Medical Physics, Faculty of Medicine, University of Crete, P.O. Box 2208, Iraklion 71003, Crete, and Department of Radiology, Faculty of Medicine, University of Crete, P. O. Box 2208, Iraklion 71003, Crete. Energy imparted-based estimates of the effect of z overscanning on adult and pediatric patient effective doses from multi-slice computed tomography. United States: N. p., 2007. Web. doi:10.1118/1.2436980.
Theocharopoulos, Nicholas, Damilakis, John, Perisinakis, Kostas, Gourtsoyiannis, Nicholas, Department of Medical Physics, Faculty of Medicine, University of Crete, P.O. Box 2208, Iraklion 71003, Crete, & Department of Radiology, Faculty of Medicine, University of Crete, P. O. Box 2208, Iraklion 71003, Crete. Energy imparted-based estimates of the effect of z overscanning on adult and pediatric patient effective doses from multi-slice computed tomography. United States. doi:10.1118/1.2436980.
Theocharopoulos, Nicholas, Damilakis, John, Perisinakis, Kostas, Gourtsoyiannis, Nicholas, Department of Medical Physics, Faculty of Medicine, University of Crete, P.O. Box 2208, Iraklion 71003, Crete, and Department of Radiology, Faculty of Medicine, University of Crete, P. O. Box 2208, Iraklion 71003, Crete. Sun . "Energy imparted-based estimates of the effect of z overscanning on adult and pediatric patient effective doses from multi-slice computed tomography". United States. doi:10.1118/1.2436980.
@article{osti_20951135,
title = {Energy imparted-based estimates of the effect of z overscanning on adult and pediatric patient effective doses from multi-slice computed tomography},
author = {Theocharopoulos, Nicholas and Damilakis, John and Perisinakis, Kostas and Gourtsoyiannis, Nicholas and Department of Medical Physics, Faculty of Medicine, University of Crete, P.O. Box 2208, Iraklion 71003, Crete and Department of Radiology, Faculty of Medicine, University of Crete, P. O. Box 2208, Iraklion 71003, Crete},
abstractNote = {In the present study effective dose values normalized to computed tomography dose index measured free in air were calculated for adult, newborn, 1, 5, 10 and 15 year old patients regarding scans of the head, chest, abdomen, pelvis, abdomen and pelvis, and trunk, using the energy imparted method. The effect of z overscanning on patient doses was accounted for, and normalized doses are provided for varying beam collimation, pitch and reconstruction slice width values. The contribution of overscanning depends on patient age, anatomic region imaged, acquisition and reconstruction settings. For a head scan it constitutes 15% of the adult effective dose and 24% of the effective dose to a newborn but for an abdomen scan it may be as high as 58% for a newborn and 31% for an adult. The ratios of normalized pediatric doses relative to that for adults for helical scans depend not only on age but also on acquisition and reconstruction parameters, because of variations in the relative distance between the primary beam and the radiosensitive tissues/organs of the body. Regarding scans of the trunk, pediatric doses are up to a factor of 2.5 times higher compared to adult doses (abdominal scans), whereas for scans of the head up to a factor of 1.5. Increasing the pitch value of helical scans while maintaining the same effective mAs setting, and hence noise levels, leads to an increase in patient doses which depends on age, body region, scan and reconstruction parameters. The % difference between doses at pitch 1.5 and pitch 1 is more pronounced in the abdominal region (14% increase for adults) and in young patients (31% in a newborn and 18% in a 10 year old patient) and it is minimal in head scans (4% increase in newborns and 1% in adults). If multiple body regions are to be imaged, doses to adults can be reduced by up to 15% and 36% to children by performing single long-range scans. Scanning adult patients at 100 kVp instead of 120 kVp, results in a 32% reduction in effective dose from head scans and 38% for scans of the torso. The corresponding reduction for a 5 year old patient is 31% for the head and 37% for the trunk. Due to the combined overbeaming and overscanning effect the 24 mm collimation is more dose effective in the head mode and the 12 mm collimation in the body mode. Provided data enable informed design of examination protocols, calculation of effective dose values and familiarization with the technical features of multi-detector technology.},
doi = {10.1118/1.2436980},
journal = {Medical Physics},
number = 4,
volume = 34,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • The purpose of this study is to provide a method and required data for the estimation of effective dose (E) values to adult and pediatric patients from computed tomography (CT) scans of the head, chest abdomen, and pelvis, performed on multi-slice scanners. Mean section radiation dose (d{sub m}) to cylindrical water phantoms of varying radius normalized over CT dose index free-in-air (CTDI{sub F}) were calculated for the head and body scanning modes of a multislice scanner with use of Monte Carlo techniques. Patients were modeled as equivalent water phantoms and the energy imparted ({epsilon}) to simulated pediatric and adult patientsmore » was calculated on the basis of measured CTDI{sub F} values. Body region specific energy imparted to effective dose conversion coefficients (E/{epsilon}) for adult male and female patients were generated from previous data. Effective doses to patients aged newborn to adult were derived for all available helical and axial beam collimations, taking into account age specific patient mass and scanning length. Depending on high voltage, body region, and patient sex, E/{epsilon} values ranged from 0.008 mSv/mJ for head scans to 0.024 mSv/mJ for chest scans. When scanned with the same technique factors as the adults, pediatric patients absorb as little as 5% of the energy imparted to adults, but corresponding effective dose values are up to a factor of 1.6 higher. On average, pediatric patients absorb 44% less energy per examination but have a 24% higher effective dose, compared with adults. In clinical practice, effective dose values to pediatric patients are 2.5 to 10 times lower than in adults due to the adaptation of tube current. A method is provided for the calculation of effective dose to adult and pediatric patients on the basis of individual patient characteristics such as sex, mass, dimensions, and density of imaged anatomy, and the technical features of modern multislice scanners. It allows the optimum selection of scanning parameters regarding patient doses a0010t.« less
  • PurposeTo compare the effective doses of needle biopsies based on dose measurements and simulations using adult and pediatric phantoms, between cone beam c-arm CT (CBCT) and CT.MethodEffective doses were calculated and compared based on measurements and Monte Carlo simulations of CT- and CBCT-guided biopsy procedures of the lungs, liver, and kidney using pediatric and adult phantoms.ResultsThe effective doses for pediatric and adult phantoms, using our standard protocols for upper, middle and lower lungs, liver, and kidney biopsies, were significantly lower under CBCT guidance than CT. The average effective dose for a 5-year old for these five biopsies was 0.36 ± 0.05 mSv withmore » the standard CBCT exposure protocols and 2.13 ± 0.26 mSv with CT. The adult average effective dose for the five biopsies was 1.63 ± 0.22 mSv with the standard CBCT protocols and 8.22 ± 1.02 mSv using CT. The CT effective dose was higher than CBCT protocols for child and adult phantoms by 803 and 590 % for upper lung, 639 and 525 % for mid-lung, and 461 and 251 % for lower lung, respectively. Similarly, the effective dose was higher by 691 and 762 % for liver and 513 and 608 % for kidney biopsies.ConclusionsBased on measurements and simulations with pediatric and adult phantoms, radiation effective doses during image-guided needle biopsies of the lung, liver, and kidney are significantly lower with CBCT than with CT.« less
  • z overscanning in multidetector (MD) helical CT scanning is prerequisite for the interpolation of acquired data required during image reconstruction and refers to the exposure of tissues beyond the boundaries of the volume to be imaged. The aim of the present study was to evaluate the effect of z overscanning on the patient effective dose from helical MD CT examinations. The Monte Carlo N-particle radiation transport code was employed in the current study to simulate CT exposure. The validity of the Monte Carlo simulation was verified by (a) a comparison of calculated and measured standard computed tomography dose index (CTDI)more » dosimetric data, and (b) a comparison of calculated and measured dose profiles along the z axis. CTDI was measured using a pencil ionization chamber and head and body CT phantoms. Dose profiles along the z axis were obtained using thermoluminescence dosimeters. A commercially available mathematical anthropomorphic phantom was used for the estimation of effective doses from four standard CT examinations, i.e., head and neck, chest, abdomen and pelvis, and trunk studies. Data for both axial and helical modes of operation were obtained. In the helical mode, z overscanning was taken into account. The calculated effective dose from a CT exposure was normalized to CTDI{sub freeinair}. The percentage differences in the normalized effective dose between contiguous axial and helical scans with pitch=1, may reach 13.1%, 35.8%, 29.0%, and 21.5%, for head and neck, chest, abdomen and pelvis, and trunk studies, respectively. Given that the same kilovoltage and tube load per rotation were used in both axial and helical scans, the above differences may be attributed to z overscanning. For helical scans with pitch=1, broader beam collimation is associated with increased z overscanning and consequently higher normalized effective dose value, when other scanning parameters are held constant. For a given beam collimation, the selection of a higher value of reconstructed image slice width increases the normalized effective dose. In conclusion, z overscanning may significantly affect the patient effective dose from CT examinations performed on MD CT scanners. Therefore, an estimation of the patient effective dose from MD helical CT examinations should always take into consideration the effect of z overscanning.« less
  • Purpose: To validate the accuracy of a Monte Carlo source model of the Siemens SOMATOM Sensation 16 CT scanner using organ doses measured in physical anthropomorphic phantoms. Methods: The x-ray output of the Siemens SOMATOM Sensation 16 multidetector CT scanner was simulated within the Monte Carlo radiation transport code, MCNPX version 2.6. The resulting source model was able to perform various simulated axial and helical computed tomographic (CT) scans of varying scan parameters, including beam energy, filtration, pitch, and beam collimation. Two custom-built anthropomorphic phantoms were used to take dose measurements on the CT scanner: an adult male and amore » 9-month-old. The adult male is a physical replica of University of Florida reference adult male hybrid computational phantom, while the 9-month-old is a replica of University of Florida Series B 9-month-old voxel computational phantom. Each phantom underwent a series of axial and helical CT scans, during which organ doses were measured using fiber-optic coupled plastic scintillator dosimeters developed at University of Florida. The physical setup was reproduced and simulated in MCNPX using the CT source model and the computational phantoms upon which the anthropomorphic phantoms were constructed. Average organ doses were then calculated based upon these MCNPX results. Results: For all CT scans, good agreement was seen between measured and simulated organ doses. For the adult male, the percent differences were within 16% for axial scans, and within 18% for helical scans. For the 9-month-old, the percent differences were all within 15% for both the axial and helical scans. These results are comparable to previously published validation studies using GE scanners and commercially available anthropomorphic phantoms. Conclusions: Overall results of this study show that the Monte Carlo source model can be used to accurately and reliably calculate organ doses for patients undergoing a variety of axial or helical CT examinations on the Siemens SOMATOM Sensation 16 scanner.« less
  • As multidetector computed tomography (CT) serves as an increasingly frequent diagnostic modality, radiation risks to patients became a greater concern, especially for children due to their inherently higher radiosensitivity to stochastic radiation damage. Current dose evaluation protocols include the computed tomography dose index (CTDI) or point detector measurements using anthropomorphic phantoms that do not sufficiently provide accurate information of the organ-averaged absorbed dose and corresponding effective dose to pediatric patients. In this study, organ and effective doses to pediatric patients under helical multislice computed tomography (MSCT) examinations were evaluated using an extensive series of anthropomorphic computational phantoms and Monte Carlomore » radiation transport simulations. Ten pediatric phantoms, five stylized (equation-based) ORNL phantoms (newborn, 1-year, 5-year, 10-year, and 15-year) and five tomographic (voxel-based) UF phantoms (9-month male, 4-year female, 8-year female, 11-year male, and 14-year male) were implemented into MCNPX for simulation, where a source subroutine was written to explicitly simulate the helical motion of the CT x-ray source and the fan beam angle and collimator width. Ionization chamber measurements were performed and used to normalize the Monte Carlo simulation results. On average, for the same tube current setting, a tube potential of 100 kVp resulted in effective doses that were 105% higher than seen at 80 kVp, and 210% higher at 120 kVp regardless of phantom type. Overall, the ORNL phantom series was shown to yield values of effective dose that were reasonably consistent with those of the gender-specific UF phantom series for CT examinations of the head, pelvis, and torso. However, the ORNL phantoms consistently overestimated values of the effective dose as seen in the UF phantom for MSCT scans of the chest, and underestimated values of the effective dose for abdominal CT scans. These discrepancies increased with increasing kVp. Finally, absorbed doses to select radiation sensitive organs such as the gonads, red bone marrow, colon, and thyroid were evaluated and compared between phantom types. Specific anatomical problems identified in the stylized phantoms included excessive pelvic shielding of the ovaries in the female phantoms, enhanced red bone marrow dose to the arms and rib cage for chest exams, an unrealistic and constant torso thickness resulting in excessive x-ray attenuation in the regions of the abdominal organs, and incorrect positioning of the thyroid within the stylized phantom neck resulting in insufficient shielding by clavicles and scapulae for lateral beam angles. To ensure more accurate estimates of organ absorbed dose in multislice CT, it is recommended that voxel-based phantoms, potentially tailored to individual body morphometry, be utilized in any future prospective epidemiological studies of medically exposed children.« less