Air kerma to dose equivalent conversion coefficients not included in ISO 4037-3

The International Organization for Standardization (ISO) has issued a standard series on photon reference radiation qualities (ISO 4037). In this work, conversion coefficients from air kerma to dose equivalent quantities not included in ISO 4037-3 are supplied for the following quantities: For H(p)(0.07) for X and gamma radiation qualities for the rod, the pillar and the slab phantom and for H(p)(3) for X and gamma radiation qualities for the slab phantom. In addition, an overview of conversion coefficients suggested for use for all quantities relevant in radiation protection is provided.     

Personal dose equivalent conversion coefficients for photons to 1 GeV

The personal dose equivalent, H(p)(d), is the quantity recommended by the International Commission on Radiation Units and Measurements (ICRU) to be used as an approximation of the protection quantity effective dose when performing personal dosemeter calibrations. The personal dose equivalent can be defined for any location and depth within the body. Typically, the location of interest is the trunk, where personal dosemeters are usually worn, and in this instance a suitable approximation is a 30 × 30 × 15 cm(3) slab-type phantom. For this condition, the personal dose equivalent is denoted as H(p,slab)(d) and the depths, d, are taken to be 0.007 cm for non-penetrating and 1 cm for penetrating radiation. In operational radiation protection a third depth, 0.3 cm, is used to approximate the dose to the lens of the eye. A number of conversion coefficients for photons are available for incident energies up to several megaelectronvolts, however, data to higher energies are limited. In this work, conversion coefficients up to 1 GeV have been calculated for H(p,slab)(10) and H(p,slab)(3) both by using the kerma approximation and tracking secondary charged particles. For H(p)(0.07), the conversion coefficients were calculated, but only to 10 MeV due to computational limitations. Additionally, conversions from air kerma to H(p,slab)(d) have been determined and are reported. The conversion coefficients were determined for discrete incident energies, but analytical fits of the coefficients over the energy range are provided. Since the inclusion of air can influence the production of secondary charged particles incident on the face of the phantom, conversion coefficients have been determined both in vacuo and with the source and slab immersed within a sphere in air. The conversion coefficients for the personal dose equivalent are compared with the appropriate protection quantity, calculated according to the recommendations of the latest International Commission on Radiological Protection (ICRP) guidance.     

Personal dose equivalent conversion coefficients for electrons to 1 Ge V

In a previous paper, conversion coefficients for the personal dose equivalent, H(p)(d), for photons were reported. This note reports values for electrons calculated using similar techniques. The personal dose equivalent is the quantity used to approximate the protection quantity effective dose when performing personal dosemeter calibrations and in practice the personal dose equivalent is determined using a 30×30×15 cm slab-type phantom. Conversion coefficients to 1 GeV have been calculated for H(p)(10), H(p)(3) and H(p)(0.07) in the recommended slab phantom. Although the conversion coefficients were determined for discrete incident energies, analytical fits of the conversion coefficients over the energy range are provided using a similar formulation as in the photon results previously reported. The conversion coefficients for the personal dose equivalent are compared with the appropriate protection quantity, calculated according to the recommendations of the latest International Commission on Radiological Protection guidance. Effects of eyewear on H(p)(3) are also discussed.     

Radiation dose from 3D rotational X-ray imaging: organ and effective dose with conversion factors

The purpose of this study was to measure organ doses and the effective dose (ED) using a three-dimensional rotational X-ray (3D-RX) system and to determine the ED conversion factor from the dose area product (DAP) for skull, spine and biliary protocols. A commercial 3D-RX imaging system was used to simulate the protocols with the adult female anthropomorphic phantom. Twenty MOSFET detectors were used to measure the absorbed doses at various organ locations. The ED was calculated for each protocol and the corresponding DAP was obtained. The skin dose was the highest for all the protocols. The second highest organ doses were those of the brain for the skull, the intestine for the spine and the kidney for the biliary protocol. The ED was 0.4-0.9, 4.2-8.4 and 3.2-4.6 mSv, and the ED conversion factor was 0.06-0.09, 0.18-0.31 and 0.13-0.23 mSv Gy(-1) cm(-2) for each protocol, respectively. This data may be used to estimate the patient ED for those protocols in the 3D-RX.     

The scope for measuring the effective dose of external irradiation and the use of operational quantities

The effective dose of external radiation may be measured as a physical quantity by an indirect method based on direct measurements of air kerma for photons, neutron fluence, or electron fluence, where calculated conversion factors for given irradiation conditions are used. The same method is used for measuring operational quantities. __________ Translated from Izmeritel’naya Tekhnika, No. 5, pp. 47–52, May, 2008.     

Determination of ambient and personal dose equivalent for personnel and cargo security screening

In the past few years, imaging technology using ionising radiation has been gaining in importance for the screening of goods and persons for security reasons and in order to detect contraband. For radiation protection purposes it is extremely important to know that dose persons are exposed to when passing through a personnel scanner or, as a stowaway, in a cargo scanner, so as to remain within the prescribed dose limits. Within the scope of a research project, measurements were performed on different types of personnel X-ray scanners as well as cargo X-ray scanners, using the transmission and/or the backscattering method. All scanners investigated operate with a high dose rate and use short irradiation time. Owing to this method of scanning reliable values can only be determined for the personal and ambient dose equivalents, H(p)(10) and H(*)(10), by using a specially developed measuring system. The aim of this project was to determine the range of magnitudes of doses for representative personnel and cargo X-ray scanner systems. Depending on the type of scanner, the determined dose values for personnel scanners range from 0.07 microSv to 6 microSv. Measurements and instruments used in this study are described and the dose values obtained are discussed in detail.     

Review of reconstruction of radiation incident air kerma by measurement of absorbed dose in tooth enamel with EPR

Electron paramagnetic resonance dosimetry with tooth enamel has been proved to be a reliable method to determine retrospectively exposures from photon fields with minimal detectable doses of 100 mGy or lower, which is lower than achievable with cytogenetic dose reconstruction methods. For risk assessment or validating dosimetry systems for specific radiation incidents, the relevant dose from the incident has to be calculated from the total absorbed dose in enamel by subtracting additional dose contributions from the radionuclide content in teeth, natural external background radiation and medical exposures. For calculating organ doses or evaluating dosimetry systems the absorbed dose in enamel from a radiation incident has to be converted to air kerma using dose conversion factors depending on the photon energy spectrum and geometry of the exposure scenario. This paper outlines the approach to assess individual dose contributions to absorbed dose in enamel and calculate individual air kerma of a radiation incident from the absorbed dose in tooth enamel.     

Tritons at energies of 10 MeV to 1 TeV: conversion coefficients for fluence-to-absorbed dose, equivalent dose, effective dose and gray equivalent, calculated using Monte Carlo radiation transport code MCNPX 2.7.C

Conversion coefficients were calculated for fluence-to-absorbed dose, fluence-to-equivalent dose, fluence-to-effective dose and fluence-to-gray equivalent for isotropic exposure of an adult female and an adult male to tritons ((3)H(+)) in the energy range of 10 MeV to 1 TeV (0.01-1000 GeV). Coefficients were calculated using Monte Carlo transport code MCNPX 2.7.C and BodyBuilder? 1.3 anthropomorphic phantoms. Phantoms were modified to allow calculation of effective dose to a Reference Person using tissues and tissue weighting factors from 1990 and 2007 recommendations of the International Commission on Radiological Protection (ICRP) and calculation of gray equivalent to selected tissues as recommended by the National Council on Radiation Protection and Measurements. At 15 of the 19 energies for which coefficients for effective dose were calculated, coefficients based on ICRP 2007 and 1990 recommendations differed by less than 3%. The greatest difference, 43%, occurred at 30 MeV.     

Helions at energies of 10 MeV to 1 TeV: conversion coefficients for fluence-to-absorbed dose, equivalent dose, effective dose and gray equivalent, calculated using Monte Carlo radiation transport code MCNPX 2.7.C

Conversion coefficients were calculated for fluence-to-absorbed dose, fluence-to-equivalent dose, fluence-to-effective dose and fluence-to-gray equivalent, for isotropic exposure of an adult male and an adult female to helions ((3)He(2+)) in the energy range of 10 MeV to 1 TeV (0.01-1000 GeV). Calculations were performed using Monte Carlo transport code MCNPX 2.7.C and BodyBuilder? 1.3 anthropomorphic phantoms modified to allow calculation of effective dose using tissues and tissue weighting factors from either the 1990 or 2007 recommendations of the International Commission on Radiological Protection (ICRP), and gray equivalent to selected tissues as recommended by the National Council on Radiation Protection and Measurements. At 15 of the 19 energies for which coefficients for effective dose were calculated, coefficients based on ICRP 2007 and 1990 recommendations differed by less than 2%. The greatest difference, 62%, occurred at 100 MeV.     

Deuterons at energies of 10 MeV to 1 TeV: conversion coefficients for fluence-to-absorbed dose, equivalent dose, effective dose and gray equivalent, calculated using Monte Carlo radiation transport code MCNPX 2.7.C

Conversion coefficients were calculated for fluence-to-absorbed dose, fluence-to-equivalent dose, fluence-to-effective dose and fluence-to-gray equivalent for isotropic exposure of an adult female and an adult male to deuterons ((2)H(+)) in the energy range 10 MeV-1 TeV (0.01-1000 GeV). Coefficients were calculated using the Monte Carlo transport code MCNPX 2.7.C and BodyBuilder? 1.3 anthropomorphic phantoms. Phantoms were modified to allow calculation of the effective dose to a Reference Person using tissues and tissue weighting factors from 1990 and 2007 recommendations of the International Commission on Radiological Protection (ICRP) and gray equivalent to selected tissues as recommended by the National Council on Radiation Protection and Measurements. Coefficients for the equivalent and effective dose incorporated a radiation weighting factor of 2. At 15 of 19 energies for which coefficients for the effective dose were calculated, coefficients based on ICRP 1990 and 2007 recommendations differed by <3%. The greatest difference, 47%, occurred at 30 MeV.     

Computation of cross sections and dose conversion factors for criticality accident dosimetry

In the application of criticality accident dosemeters the cross sections and fluence-to-dose conversion factors have to be computed. The cross section and fluence-to-dose conversion factor for the thermal and epi-thermal contributions to neutron dose are well documented; for higher energy regions (>100 keV) these depend on the spectrum assumed. Fluence is determined using threshold detectors. The cross sections require the folding of an expected spectrum with the reaction cross sections. The fluence-to-dose conversion factors also require a similar computation. The true and effective thresholds are used to include the information on the expected spectrum. The spectra can either be taken from compendia or measured at the facility at which the exposures are to be expected. The cross sections can be taken from data computations or analytic representations and the fluence-to-dose conversion factors are determined by various standards making bodies. The problem remaining is the method of computation. The purpose of this paper is to compare two methods for computing these factors: analytic and Monte Carlo.     

Features of spectra of low-energy neon ions scattered from gallium phosphide

Using mass-resolved ion scattering spectrometry, spectra of Ne⁺ ions scattered at an angle of 120° from the surface of GaP in the energy range of 0.4–1.96 keV have been studied in detail. In the spectra, in addition to the peaks of elastic binary Ne⁺/P and Ne⁺/Ga collisions, the peak of sputtered neon ions has been found, as well as the wide peak (a “hump”), the energy of which slightly depends on the energy of primary ions and the intensity considerably increases with an increase in this energy. In our opinion, the main contribution to this peak is made by neon ions that undergo multiple collisions with gallium and phosphorus atoms on the surface and deeper layers of the sample and keep their charge due to reionization processes.     

Air kerma to Hp(3) conversion coefficients for a new cylinder phantom for photon reference radiation qualities

The International Organization for Standardization (ISO) has issued a standard series on photon reference radiation qualities (ISO 4037). In this series, no conversion coefficients are contained for the quantity personal dose equivalent at a 3 mm depth, H(p)(3). In the past, for this quantity, a slab phantom was recommended as a calibration phantom; however, a cylinder phantom much better approximates the shape of a human head than a slab phantom. Therefore, in this work, the conversion coefficients from air kerma to H(p)(3) for the cylinder phantom are supplied for X- and gamma radiation qualities defined in ISO 4037.     

Cut-HDMR-based fully equivalent operational model for analysis of unreinforced masonry structures

Mesoscale models are highly competent for understanding behaviour of unreinforced masonry structures. Their only limitation is large computational expense. Fully Equivalent Operational Model forms an equivalent mathematical model to represent a particular phenomenon where explicit relationship between inputs and outputs are unknown. This paper explores the ability of a major variant of High Dimensional Model Representation (HDMR) technique, namely Cut-HDMR, to construct the most efficient Fully Equivalent Operational Model for nonlinear finite element analysis of mesoscale model of an unreinforced masonry structure. Conclusions are reached on various aspects such as, suitability of interpolation schemes and order of Cut-HDMR approximation.     

Corrections to air kerma and exposure measured with free air ionisation chambers for charge of photoelectrons, Compton electrons and Auger electrons

The signal charge from a free air ionisation chamber for the measurement of air kerma and exposure consists of not only the charge of ion pairs produced by secondary electrons (i.e. photoelectrons, Compton electrons and Auger electrons), but also the charge of the secondary electrons and single and multiple charged ions formed by the release of the secondary electrons. In the present work, correction factors for air kerma and exposure for the charge of the secondary electrons and ions were calculated for photons with energies in the range from 1 to 400 keV. The effects of an increase in the W value of air for low-energy electrons were also taken into consideration. It was found that the correction factors for air kerma and exposure have a maximum value near a photon energy of 30 keV; in the lower energy region, the correction factor for exposure monotonically decreases with a decrease in photon energy except for a small dip due to K-edge absorption by argon atoms in air. The values of the correction factors were found to be 0.9951 and 0.9892, respectively, for a spectrum with a mean energy of 7.5 keV, the reference X-ray spectrum with the lowest mean energy in ISO 4037-1. The air kerma correction is smaller than that for exposure, because for air kerma the signal due to the charge of secondary electrons and ions is partly compensated by the decrease in the number of ion pairs produced by the secondary electrons due to the increase of the W value of air for lower energy electrons.     

Error reduction in conversion of analog quantities to digitized time intervals

Measurement Techniques - 1. It is possible to reduce the systematic errors in analog-time-digital conversion if additional parallel conversion channel is used for a reference quantity comparable...     

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.     

Estimation of the peak entrance surface air kerma for patients undergoing computed tomography-guided procedures

The purpose of this work was to develop a method for estimating the patient peak entrance surface air kerma from measurements using a pencil ionisation chamber on dosimetry phantoms exposed in a computed tomography (CT) scanner. The method described is especially relevant for CT fluoroscopy and CT perfusion procedures where the peak entrance surface air kerma is the risk-related quantity of primary concern. Pencil ionisation chamber measurements include scattered radiation, which is outside the primary radiation field, and that must be subtracted in order to derive the peak entrance surface air kerma. A Monte Carlo computer model has therefore been used to calculate correction factors, which may be applied to measurements of the CT dose index obtained using a pencil ionisation chamber in order to estimate the peak entrance surface air kerma. The calculations were made for beam widths of 5, 7, 10 and 20 mm, for seven positions of the phantom, and for the geometry of a GE HiSpeed CT/i scanner. The program was validated by comparing measurements and calculations of CTDI for various vertical positions of the phantom and by directly estimating the peak ESAK using the program. Both validations showed agreement within statistical uncertainties (standard deviation of 2.3% or less). For the GE machine, the correction factors vary by approximately 10% with slice width for a fixed phantom position, being largest for the 20 mm beam width, and at that beam width range from 0.87 when the phantom surface is at the isocentre to 1.23 when it is displaced vertically by 24 cm.     

Double-differential spectra of secondary particles from hadrons on tissue equivalent targets

Double-differential spectra generated by ions on tissue equivalent targets were calculated with the FLUKA code. Seven different species of ion beams were simulated, impinging onto an ICRU tissue equivalent target representing the chest of a patient under treatment. The following ion beams were investigated at an energy level capable of penetrating ICRU tissue up to a 26.2 cm depth: H, He, Li, B, C, N and O at 200.0, 202.0, 234.3, 329.5, 390.7, 430.5 and 468.0 MeV u(-1), respectively. The double-differential spectra of secondary neutrons, protons, photons, positive and negative pions, electrons and positrons were scored over the entire solid angle. Curve-fitting of the calculated data is also given.