Article

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

Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institute of Health, Bethesda, Maryland 20852, USA.
Medical Physics (Impact Factor: 2.64). 03/2011; 38(3):1196-206. DOI: 10.1118/1.3544658
Source: PubMed

ABSTRACT

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.

Download full-text

Full-text

Available from: Steven L Simon, Dec 17, 2013
    • "The basis of the program is a series of hybrid paediatric phantoms that represent reference individuals at the age of 0 year, 1 year, 5 years, 10 years, and 15 years (Fig. 1, left)[17], and reflect the anatomical and physiological data provided in the ICRP Publication 89[18]. New sets of organ and effective doses normalized to the volumetric CT Dose Index (CTDI vol )[19]based on the hybrid phantom series coupled with the Monte Carlo simulation of a reference CT scanner were incorporated into the NCICT pro- gram[20,21]. NCICT has been experimentally validated using anthropomorphic physical phantoms, and is being used in the framework of EPI-CT[8,9]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Objective To assess the range of doses in paediatric CT scans conducted in the 1990s in Norway as input to an international epidemiology study: the EPI-CT study, http:// epi-ct. iarc. fr/ . Methods National Cancer Institute dosimetry system for Computed Tomography (NCICT) program based on pre-calculated organ dose conversion coefficients was used to convert CT Dose Index to organ doses in paediatric CT in the 1990s. Protocols reported from local hospitals in a previous Norwegian CT survey were used as input, presuming these were used without optimization for paediatric patients. Results Large variations in doses between different scanner models and local scan parameter settings are demonstrated. Small children will receive a factor of 2–3 times higher doses compared with adults if the protocols are not optimized for them. For common CT examinations, the doses to the active bone marrow, breast tissue and brain may have exceeded 30 mGy, 60 mGy and 100 mGy respectively, for the youngest children in the 1990s. Conclusions The doses children received from non-optimised CT examinations during the 1990s are of such magnitude that they may provide statistically significant effects in the EPI-CT study, but probably do not reflect current practice. Key Points • Some organ doses from paediatric CT in the 1990s may have exceeded 100 mGy. • Small children may have received doses 2–3 times higher compared with adults. • Different scanner models varied by a factor of 2–3 in dose to patients. • Different local scan parameter settings gave dose variations of a factor 2–3. • Modern CTs and age-adjusted protocols will give much lower paediatric doses.
    No preview · Article · Jan 2016 · European Radiology
  • Source
    • "The GE LightSpeed Pro 16 scanner (figure 2), operated at different tube voltages (i.e., 80, 100, 120, and 140 kVp) with different beam collimations (1.25, 5, 10, and 20 mm), was developed and validated using a previously validated method by Gu et al (2009) that was later refined by Ding (2012). The SOMATOM Sensation 16 was simulated by Lee et al (2011), operated at 80, 100, 120, and 140 kVp with two beam collimations of 10 and 24 mm. It had been shown by Turner et al (2010) that organ doses normalized by CTDI vol were practically independent of the scanner type. "
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper describes the development and testing of VirtualDose-a software for reporting organ doses for adult and pediatric patients who undergo x-ray computed tomography (CT) examinations. The software is based on a comprehensive database of organ doses derived from Monte Carlo (MC) simulations involving a library of 25 anatomically realistic phantoms that represent patients of different ages, body sizes, body masses, and pregnant stages. Models of GE Lightspeed Pro 16 and Siemens SOMATOM Sensation 16 scanners were carefully validated for use in MC dose calculations. The software framework is designed with the 'software as a service (SaaS)' delivery concept under which multiple clients can access the web-based interface simultaneously from any computer without having to install software locally. The RESTful web service API also allows a third-party picture archiving and communication system software package to seamlessly integrate with VirtualDose's functions. Software testing showed that VirtualDose was compatible with numerous operating systems including Windows, Linux, Apple OS X, and mobile and portable devices. The organ doses from VirtualDose were compared against those reported by CT-Expo and ImPACT-two dosimetry tools that were based on the stylized pediatric and adult patient models that were known to be anatomically simple. The organ doses reported by VirtualDose differed from those reported by CT-Expo and ImPACT by as much as 300% in some of the patient models. These results confirm the conclusion from past studies that differences in anatomical realism offered by stylized and voxel phantoms have caused significant discrepancies in CT dose estimations.
    Full-text · Article · Jul 2015 · Physics in Medicine and Biology
  • Source
    • "In this in-air simulation, only the CT scanner and the ion chamber were modeled. Because of lack of ion chamber information, parameters for the ion chamber reported in previous studies (Gu et al 2009, Lee et al 2011) "
    [Show abstract] [Hide abstract]
    ABSTRACT: With the rapidly growing number of CT examinations, the consequential radiation risk has aroused more and more attention. The average dose in each organ during CT scans can only be obtained by using Monte Carlo simulation with computational phantoms. Since children tend to have higher radiation sensitivity than adults, the radiation dose of pediatric CT examinations requires special attention and needs to be assessed accurately. So far, studies on organ doses from CT exposures for pediatric patients are still limited. In this work, a 1-year-old computational phantom was constructed. The body contour was obtained from the CT images of a 1-year-old physical phantom and the internal organs were deformed from an existing Chinese reference adult phantom. To ensure the organ locations in the 1-year-old computational phantom were consistent with those of the physical phantom, the organ locations in 1-year-old computational phantom were manually adjusted one by one, and the organ masses were adjusted to the corresponding Chinese reference values. Moreover, a CT scanner model was developed using the Monte Carlo technique and the 1-year-old computational phantom was applied to estimate organ doses derived from simulated CT exposures. As a result, a database including doses to 36 organs and tissues from 47 single axial scans was built. It has been verified by calculation that doses of axial scans are close to those of helical scans; therefore, this database could be applied to helical scans as well. Organ doses were calculated using the database and compared with those obtained from the measurements made in the physical phantom for helical scans. The differences between simulation and measurement were less than 25% for all organs. The result shows that the 1-year-old phantom developed in this work can be used to calculate organ doses in CT exposures, and the dose database provides a method for the estimation of 1-year-old patient doses in a variety of CT examinations.
    Full-text · Article · Aug 2014 · Physics in Medicine and Biology
Show more