Organ Dose Conversion Coefficients Research Articles

Organ dose conversion coefficients for voxel models of the reference male and female from idealized photon exposures

A new series of organ equivalent dose conversion coefficients for whole body external photon exposure is presented for a standardized couple of human voxel models, called Rex and Regina. Irradiations from broad parallel beams in antero-posterior, postero-anterior, left- and right-side lateral directions as well as from a 360° rotational source have been performed numerically by the Monte Carlo transport code EGSnrc. Dose conversion coefficients from an isotropically distributed source were computed, too. The voxel models Rex and Regina originating from real patient CT data comply in body and organ dimensions with the currently valid reference values given by the International Commission on Radiological Protection (ICRP) for the average Caucasian man and woman, respectively. While the equivalent dose conversion coefficients of many organs are in quite good agreement with the reference values of ICRP Publication 74, for some organs and certain geometries the discrepancies amount to 30% or more. Differences between the sexes are of the same order with mostly higher dose conversion coefficients in the smaller female model. However, much smaller deviations from the ICRP values are observed for the resulting effective dose conversion coefficients. With the still valid definition for the effective dose (ICRP Publication 60), the greatest change appears in lateral exposures with a decrease in the new models of at most 9%. However, when the modified definition of the effective dose as suggested by an ICRP draft is applied, the largest deviation from the current reference values is obtained in postero-anterior geometry with a reduction of the effective dose conversion coefficient by at most 12%.

Fluence to organ dose conversion coefficients calculated with the voxel model NORMAN-05 and the MCNPX Monte Carlo code for external monoenergetic photons from 20 keV to 100 MeV

Photons conversion coefficients from 20 keV to 100 MeV have been calculated with the voxel model NORMAN-05 using the MCNPX code. Both kerma approximation and electronic transport were employed and the results compared with published data. In the near future, ICRP group DOCAL will issue a new computational model, based on the GSF-GOLEM, which is intended to be the reference adult male voxel model for ICRP. NORMAN-05 well approximates the western-caucasian standard man characteristics, in terms of body height (176 cm) and mass (73 kg) and masses of the organs. It is not intended to substitute, or to be an alternative, to the future official ICRP voxel model, but thanks to its accuracy and its "standard man structure" can be useful to evaluate the intrinsic uncertainties associated with the dose quantities evaluated adopting different voxel models. For such reason data obtained with NORMAN-05 could be easily compared with those that will be derived from the future ICRP model.

Age-dependent organ and effective dose coefficients for external photons: a comparison of stylized and voxel-based paediatric phantoms

This present study investigates the anatomical realism of conventional stylized models of children by comparing organ dose conversion coefficients for the ORNL paediatric phantom series with those determined in the UF (University of Florida) voxel paediatric phantoms. The latter includes whole-body models of a 9 month male, 4 year female, 8 year female, 11 year male and a 14 year male. Of these phantoms, the 1 year, 5 year and 10 year ORNL phantoms, and 9 month male, 4 year female and 11 year male UF voxel phantoms were selected for side-by-side comparisons under idealized external photon irradiation. Organ absorbed dose per unit air kerma (Gy/Gy) for various radiosensitive organs and tissues were calculated for monoenergetic photons over the energy range of 15 keV to 10 MeV and for six irradiation geometries: anterior–posterior (AP), posterior–anterior (PA), right lateral (RLAT), left lateral (LLAT), rotational (ROT) and isotropic (ISO). Differences in organ dose conversion coefficients for the gonads, bone marrow, colon, lung and stomach, to which prominent tissue weighting factors are assigned, were depicted and analysed. Two major causes of observed differences were suggested: differences in organ shape and position and the differences in tissue shielding by overlying tissue regions within the phantoms. Significant discrepancies caused by anatomical differences between the two types of phantoms are also reported for several organs, and in particular, the thyroid and urinary bladder. The results of this study suggest that the paediatric series of ORNL phantoms also have less realistic internal organ and body anatomy and that dose conversion coefficients from these stylized phantoms should be re-evaluated using paediatric voxel phantoms.

Authors' reply

CorrespondenceAuthors' replyB M MooresB M Moores1Co-ordinator, Radiological Unification Strategies [RADIUS] Group, EC Radiation Protection Research ProgrammeSearch for more papers by this authorPublished Online:13 Feb 2014https://doi.org/10.1259/bjr/71189157SectionsPDF/EPUBFull Text ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail About"Authors' reply." The British Journal of Radiology, 79(940), pp. 357–358 References 1 Shrimpton PC, Wall BF, Jones DG, Fisher ES, Hillier MC, Kendall GM. A national survey of doses to patients undergoing a selection of routine x-ray examinations in English hospitals. NRPB-R200. Chilton, UK: National Radiological Protection Board 1986. Google Scholar2 National protocol for patient dose measurements in diagnostic radiology. Chilton, Didcot: National Radiological Protection Board 1992. Google Scholar3 Rowley KA, Hill SJ, Watkins R, Moores BM. An investigation into the levels of radiation exposure in diagnostic examinations involving fluoroscopy. Br J Radiol 1987;60:167–73. Link ISI, Google Scholar4 Gallini RE, Belletti S, Berna V, Giugni U. Adult and child doses in standardised x-ray examinations. Radiat Prot Dosim 1992;43:41–7. Crossref ISI, Google Scholar5 Zankl M, Fill U, Petoussi-Henss N, Regulla D. Organ dose conversion coefficients for external photon irradiation of male and female voxel models. Phys Med Biol 2002;47:2367–85. Crossref Medline ISI, Google Scholar6 Kramer R, Vieira JW, Khoury HJ, Lima FRA, Fuelle D. All about MAX: a male adult voxel phantom for Monte Carlo calculations in radiation protection dosimetry. Phys Med Biol 2003;48:1239–62. Crossref Medline ISI, Google Scholar7 Kramer R, Khoury HJ, Vieira JW, Loureiro ECM, Lima VJM, Lima FRA, et al. All about FAX: a female adult voxel phantom for Monte Carlo calculation in radiation protection dosimetry. Phys Med Biol 2004;49:5203–16. Crossref Medline ISI, Google Scholar8 Pascoal A, Patel R, Lawinski CP, Tabakov S. Optimization of tube voltage and dose for digital chest radiography – a study addressing patient size. In: Proceedings of UK Radiological Congress, 6–8 June, 2005. London, UK: British Institute of Radiology 2005. 2 Google Scholar9 Wall BF, Rae S, Darby SC, Kendall GM. The NRPB survey: methods and results. Dosimetry in diagnostic radiology, CRS 40. Chapter 6, 44–55. The Hospital Physicists Association 1984. Google Scholar10 Goodenough DJ. Lessons learned in radiology. Proceedings of an international conference held in Malaga, Spain, 26–30 March 2001, 145–155. International Atomic Energy Agency 2001. Google Scholar11 Faulkner K, Moores BM. Radiation dose and somatic risk from computed tomography. Acta Radiologica 1987;28:483–8. Crossref Medline ISI, Google Scholar12 Harrison RM. Dose measurement in vivo and in vitro. CRS 40. Chapter 2, 8–17. The Hospital Physicist's Association. 1984. Google Scholar13 TGR 32 Measurement of the performance characteristics of diagnostic X-ray systems used in medicine. Part 1: X-ray tubes and generators. The Hospital Physicist's Association. 1984. Google Scholar Previous article Next article FiguresReferencesRelatedDetails Volume 79, Issue 940April 2006Pages: 275-361 © The British Institute of Radiology History ReceivedNovember 18,2005RevisedJanuary 04,2006AcceptedJanuary 11,2006Published onlineFebruary 13,2014 Metrics Download PDF

Optimisation strategies and justification: an example in uterine artery embolisation for fibroids

Radiation risk has to be justified and optimised. This study discusses the radiation risk of uterine artery embolisation (UAE) for the treatment of fibroids. A total of 70 consecutive UAE dosimetry parameters were assessed. Using Monte Carlo simulation, organ and effective doses and dose conversion coefficients (DCCs) (mSv Gy cm(-2)) were calculated. During UAE optimisation, avoidance of oblique views and use of last-image-hold (LIH) documentation instead of digital subtraction angiography (DSA) were investigated. Mean dose-area product (DAP) was 37.1 Gy cm2 (median 23.7 Gy cm2) and mean fluoroscopy time was 18.4 min (median 16.6 min). Dose values decreased as the study progressed: mean DAP for patients 1-21, 68.5 Gy cm2; patients 22-43, 35.7 Gy cm2; and patients 44-69, 13.0 Gy cm2. Average DCC for DSA image procedures was 0.572, yielding a mean effective dose of 29.6 mSv (median 17.1 mSv). For LIH-only procedures, an average DCC of 0.813 was estimated [using mean effective dose: 10.6 mSv (median 8.1 mSv)].

Organ and effective dose conversion coefficients for radiographic examinations of the pediatric skull estimated by Monte Carlo methods

The objective of the present work was to provide precise effective and organ dose data for radiographic examinations of the skull performed on pediatric patients. To accomplish this, the MCNP4C2 transport code was utilized and 18 mathematical anthropomorphic phantoms, representing ages from a newborn child to a 17-year-old adolescent, were developed. Three common projections, anterior-posterior, posterior-anterior and lateral, were considered. The results consist of effective and organ radiation doses normalized to the entrance surface dose. Normalized data are presented for a wide range of peak kilovoltages and beam filtration values so that doses for any X-ray unit can be calculated. Both organ and effective dose values showed an inverse correlation with age. Good agreement was observed between the normalized effective doses produced in this study and values derived from calculations based on the National Radiological Protection Board coefficients for specific mathematical phantoms representing 1-, 5-, 10- and 15-year-old children. In the present work, dose data for nine mathematical phantoms representing 0-, 1-, 2-, 3-, 4-, 5-, 6-, 9- and 14-year-old pediatric patients were provided for estimation of organ and effective doses delivered to pediatric patients from radiographic examinations of the skull.

MAX meets ADAM: a dosimetric comparison between a voxel-based and a mathematical model for external exposure to photons

The International Commission on Radiological Protection intends to revise the organ and tissue equivalent dose conversion coefficients published in various reports. For this purpose the mathematical human medical internal radiation dose (MIRD) phantoms, actually in use, have to be replaced by recently developed voxel-based phantoms. This study investigates the dosimetric consequences, especially with respect to the effective male dose, if not only a MIRD phantom is replaced by a voxel phantom, but also if the tissue compositions and the radiation transport codes are changed. This task will be resolved by systematically replacing in the mathematical ADAM/GSF exposure model, first the radiation transport code, then the tissue composition and finally the phantom anatomy, in order to arrive at the voxel-based MAX/EGS4 exposure model. The results show that the combined effect of these replacements can decrease the effective male dose by up to 25% for external exposures to photons for incident energies above 30 keV for different field geometries, mainly because of increased shielding by a heterogeneous skeleton and by the overlying adipose and muscle tissue, and also because of the positions internal organs have in a realistically designed human body compared to their positions in the mathematically constructed phantom.

Organ dose conversion coefficients for external photon irradiation of male and female voxel models

New organ equivalent dose conversion coefficients are presented for whole body irradiation with monoenergetic photons of energies between 10 keV and 10 MeV for idealized geometries and seven adult male and female voxel models. The geometries are broad parallel photon beams in anterior–posterior, posterior–anterior, left- and right-lateral direction and a full 360° rotation around the body length axis. Dose differences between the different voxel models are below approximately 30% for some organs and geometries in the energy range between 60 and 200 keV, but they can be up to 100% or more in single cases, due to differences in stature and individual anatomical details. For low photon energies, the differences may amount to hundreds of per cent. Extensive comparisons of the dose conversion coefficients with respective values calculated using mathematical body models revealed various degrees of unrealistic positioning of single organs in the latter models. Examples are the kidneys, spleen and stomach that are located too superficially in the mathematical models. Over- or underestimations of several tens of per cent may, thus, occur for the mathematical models, compared to the voxel models considered. In contrast to previous assumptions, when the mathematical models have been used to establish reference organ dose conversion coefficients, it can be concluded that they do not properly represent a large population of individuals.

Fluence to effective dose conversion coefficients for electrons with energy from 1 MeV to 100 GeV.

Fluence to organ dose and effective dose conversion coefficients have been calculated for electrons from 1 MeV to 100 GeV using an anthropomorphic phantom and the EGS4 code. The conversion coefficients were calculated for six typical irradiation geometries taking electromagnetic cascade shower and photonuclear reactions into account. The contribution to the absorbed dose due to the photonuclear reactions in energies up to 140 MeV was evaluated to be less than 0.2%. Even at energies above 140 MeV the dose contributions of the photonuclear reactions were insignificant.

Dosimetry of Occupationally Exposed Persons in Diagnostic and Interventional Arteriography. Part 2: Assessment of Effective Dose

This study aimed to quantify effective dose (E) for occupationally exposed persons (workers) in diagnostic and interventional arteriography. Using Monte Carlo radiation transport calculation, new air kerma to organ dose conversion coefficients (DCCs) were determined. Taking attenuation by protective clothing into account, E was estimated from the DCCs and entrance doses measured at forehead, neck, thorax, abdomen, upper arms, hands and lower legs of the workers. Average E was calculated for several types of procedures and for three hospitals. For operators, E was between 0.5 and 7 µSv per procedure for undercouch X ray tubes and between 0.8 and 22 µSv for overcouch tubes. For assistants, E was typically a factor of two lower. Wearing a thyroid collar roughly reduced E by 50%. These values are low, which is due, among other things, to the nearly general use of a mechanical contrast injector and an undercouch X ray tube.

Patient dosimetry in abdominal arteriography

This study aims at accurate quantification of x-ray exposure and effective dose to the patient in abdominal arteriography. Using an automatic monitoring system, all relevant exposure parameters were determined during 172 abdominal arteriographies. Common projections were extracted for a `normal' reference group of procedures and used in Monte Carlo calculations of dose-area product to organ dose conversion coefficients. Dose-area product, organ doses and effective dose were quantified for intravenous and intra-arterial procedures. The large data sets describing exposure could be condensed to a set of 28 common views. New coefficients to convert dose-area product to organ equivalent dose and effective dose were calculated for nine views contributing approximately 80% to the total dose-area product. The average dose-area product was in intravenous procedures and in intra-arterial procedures. The corresponding average effective doses to the patient were 4 mSv and 6 mSv respectively (range 2-12 mSv, actual value depending on procedure type and gender). It is concluded that automatic monitoring of x-ray exposure parameters, complemented by the calculation of Monte Carlo organ dose conversion coefficients, is a feasible and promising approach to accurate dosimetry of complex arteriographic procedures.

Methods for Assessing Organ Doses using Computational Models

The radiation risk from ionising radiation in different organs and tissues of the human body may he quantified using equivalent dose. As organ doses usually cannot be measured directly in patients, it is necessary to establish suitable conversion coefficients between organ doses and measurable dose quantities. For this purpose, computer codes, often based on Monte Carlo techniques, simulating the radiation transport in material are commonly used together with computational models of the human body. Most computational body models in use are mathematical models, in which mathematical expressions representing simple geometrical bodies are used to describe idealised arrangements of body organs. Additionally, tomographic models were developed in recently ears which use computed tomographic data of real persons to provide three-dimensional representations of the body. Using these computational models, numerous studies concerning organ and tissue doses from diagnostic radiology were performed. Organ dose conversion coefficients from various types examinations are available in the literature. In some of these studies, the influence of single technical exposure conditions (e.g tube v oltage. filtration, field size and location and focus-to-skin distance) on organ and tissue doses was examined. Additionally, the tomographic models enable the assessment of the influence of moderate vanations of the patient size on organ doses. They, therefore, improve the applicability of data for deriving doses to individual patients.