Influence of neutron cross-section resonances on organ/tissue equivalent and effective dose coefficients for the ICRP voxel phantoms.

The materials which compose the ICRP Voxel phantoms used in the computation of conversion coefficients involve neutron interaction cross-sections that have resonances at specific energies. Depending on the energy bin structure used in the computations, these cross-section resonances may occur at energies that fall between energies at which dose coefficients are computed, thus their effects may not be completely accounted for in the reported coefficients. In the present study, a highly refined energy grid that closely follows the resonance structure in the phantom material cross-sections was identified and used to calculate dose coefficients. Both the equivalent organ/tissue doses for male and female voxel phantoms were computed as well as their summation to obtain the effective dose coefficients. The used refined energy grid tracks very closely the cross-sections in the vicinity of the resonances. The resulting refined energy grid coefficients are compared to coefficients for the coarser energy grid used in ICRP Publication 116. Additionally, reference spectra have been folded with both the fine and coarse sets of conversion coefficients. The resulting total effective doses for these reference spectra are used to assess the adequacy of the dose coefficients calculated on the original ICRP 116 energy grid. The dose coefficients were similarly computed for the local skin dose on the trunk of the body using the ICRU Report 95 phantom. The overall impact of the resonances on the organ/tissue equivalent dose, the effective dose, and the local skin dose are presented and discussed. In general, it was found that resonances can impact neutron dose coefficients, but in most cases the wide range of neutron energies encountered minimized this effect. The impact of resonances was further limited when computing effective dose due to organ/tissue summing and sex-averaging. For the neutron fields studied here, the impact was below 5%.

Dose length product to effective dose coefficients in adults.

OBJECTIVES: The most accurate method for estimating patient effective dose (a principal metric for tracking patient radiation exposure) from computed tomography (CT) requires time-intensive Monte Carlo simulation. A simpler method multiplies a scalar coefficient by the widely available scanner-reported dose length product (DLP) to estimate effective dose. We developed new adult effective dose coefficients using actual patient scans and assessed their agreement with Monte Carlo simulation. METHODS: A multicenter sample of 216,906 adult CT scans was prospectively assembled in 2015-2020 from the University of California San Francisco International CT Dose Registry and the University of Florida library of computational phantoms. We generated effective dose coefficients for eight body regions, stratified by patient sex, diameter, and scanner manufacturer. We applied the new coefficients to DLPs to calculate effective doses and assess their correlations with Monte Carlo radiation transport-generated effective dose. RESULTS: Effective dose coefficients varied by body region and decreased in magnitude with increasing patient diameter. Coefficients were approximately twofold higher for torso scans in smallest compared with largest diameter categories. For example, abdomen and pelvis coefficients decreased from 0.027 to 0.013 mSv/mGy-cm between the 16-20 cm and 41+ cm categories. There were modest but consistent differences by sex and manufacturer. Diameter-based coefficients used to estimate effective dose produced strong correlations with the reference standard (Pearson correlations 0.77-0.86). The reported conversion coefficients differ from previous studies, particularly in neck CT. CONCLUSIONS: New effective dose coefficients derived from empirical clinical scans can be used to easily estimate effective dose using scanner-reported DLP. CLINICAL RELEVANCE STATEMENT: Scalar coefficients multiplied by DLP offer a simple approximation to effective dose, a key radiation dose metric. New effective dose coefficients from this study strongly correlate with gold standard, Monte Carlo-generated effective dose, and differ somewhat from previous studies. KEY POINTS: • Previous effective dose coefficients were derived from theoretical models rather than real patient data. • The new coefficients (from a large registry/phantom library) differ from previous studies. • The new coefficients offer reasonably reliable values for estimating effective dose.

131I dose coefficients for a reference population using age-specific models.

Age-specific dose coefficients are required to assess internal exposure to the general public. This study utilizes reference age-specific biokinetic models of iodine to estimate the total number of nuclear disintegrations ã(rS,τ) occurring in source regions (rS) during the commitment time (τ). Age-specific S values are estimated for 35 target regions due to131I present in 22rSusing data from 10 paediatric reference computational phantoms (representing five ages for both sexes) published recently by the International Commission of Radiation Protection (ICRP). Monte Carlo transport simulations are performed in FLUKA code. The estimated ã(rS,τ) and S values are then used to compute the committed tissue equivalent dose HT(τ) for 27 radiosensitive tissues and dose coefficients e(τ) for all five ages due to inhalation and ingestion of131I. The derived ã(rS,τ) values in the thyroid source are observed to increase with age due to the increased retention of iodine in the thyroid. S values are found to decrease with age, mainly due to an increase in target masses. Generally, HT(τ) values are observed to decrease with age, indicating the predominant behaviour of S values over ã(rS,τ). On average, ingestion dose coefficients are 63% higher than for inhalation in all ages. The maximum contribution to dose coefficients is from the thyroid, accounting for 96% in the case of newborns and 98%-99% for all other ages. Furthermore, the estimated e(τ) values for the reference population are observed to be lower than previously published reference values from the ICRP. The estimated S, HT(τ) and e(τ) values can be used to improve estimations of internal doses to organs/whole body for members of the public in cases of131I exposure. The estimated dose coefficients can also be interpolated for other ages to accurately evaluate the doses received by the general public during131I therapy or during a radiological emergency.

Dose length product to effective dose coefficients in children.

BACKGROUND: The most accurate method for estimating effective dose (the most widely understood metric for tracking patient radiation exposure) from computed tomography (CT) requires time-intensive Monte Carlo simulation. A simpler method multiplies a scalar coefficient by the widely available scanner-reported dose length product (DLP) to estimate effective dose. OBJECTIVE: Develop pediatric effective dose coefficients and assess their agreement with Monte Carlo simulation. MATERIALS AND METHODS: Multicenter, population-based sample of 128,397 pediatric diagnostic CT scans prospectively assembled in 2015-2020 from the University of California San Francisco International CT Dose Registry and the University of Florida library of highly realistic hybrid computational phantoms. We generated effective dose coefficients for seven body regions, stratified by patient age, diameter, and scanner manufacturer. We applied the new coefficients to DLPs to calculate effective doses and assessed their correlations with Monte Carlo radiation transport-generated effective doses. RESULTS: The reported effective dose coefficients, generally higher than previous studies, varied by body region and decreased in magnitude with increasing age. Coefficients were approximately 4 to 13-fold higher (across body regions) for patients <1 year old compared with patients 15-21 years old. For example, head CT (54% of scans) dose coefficients decreased from 0.039 to 0.003 mSv/mGy-cm in patients <1 year old vs. 15-21 years old. There were minimal differences by manufacturer. Using age-based conversion coefficients to estimate effective dose produced moderate to strong correlations with Monte Carlo results (Pearson correlations 0.52-0.80 across body regions). CONCLUSIONS: New pediatric effective dose coefficients update existing literature and can be used to easily estimate effective dose using scanner-reported DLP.

Development of a generalized method to allow the estimation of doses to the ICRP reference adults from CT, on the basis of normalized organ and CTDI dose data determined by Monte Carlo calculation for a range of contemporary scanners.

Objective. Development of a method to provide organ and effective dose coefficients to reference adults for any CT scanner based on values ofCTDImeasured both in air and in standard CT dosimetry phantoms.Approach. Results from previous Monte Carlo simulations for a range of contemporary CT scanners have been analyzed to provide linear models relating values of organ dose (normalized toCTDIfree-in-air), for each slab of 3 reference phantoms (ICRP Male/Female, and AH hermaphrodite), to similarly normalized values ofCTDIin standard CT dosimetry phantoms. Three methods have been investigated to apply the models to values ofCTDIfor a 'new' scanner not previously simulated: a Generic approach using averaged normalized organ dose profiles for whole body exposure of the phantoms; and two processes for matching the scanner, on the basis of normalized organ doses or effective dose (nE103,phan), to one of the 102 sets of dose coefficients previously calculated for 12 contemporary CT scanner models, from 4 manufacturers, operating under a range of conditions.Main results. The merit of each method has been quantitatively assessed when applied to both the present contemporary scanners with each test data set being excluded in turn during the matching process, and also to 3 previously-simulated older scanners. Whereas all three methods appear viable, with all doses being within 1% and 10% for the contemporary and old scanners respectively, matching tonE103,phanis overall the approach preferred in practice, yielding an uncertainty of around 6% in estimated values ofnE103,phan. The present methodology also provides superior performance when compared against some other common normalization factors forE103,phan.Significance. The CT dose model and the data sets will be incorporated into a new CT dosimetry tool that will be made available from UKHSA in support of facilitating improvements in patient protection.

Biokinetics and Internal Dosimetry of Tritiated Steel Particles.

Decommissioning fission and fusion facilities can result in the production of airborne particles containing tritium that could inadvertently be inhaled by workers directly involved in the operations, and potentially others, resulting in internal exposures to tritium. Of particular interest in this context, given the potentially large masses of material involved, is tritiated steel. The International Commission on Radiological Protection (ICRP) has recommended committed effective dose coefficients for inhalation of some tritiated materials, but not specifically for tritiated steel. The lack of a dose coefficient for tritiated steel is a concern given the potential importance of the material. To address this knowledge gap, a "dissolution" study, in vivo biokinetic study in a rodent model (1 MBq intratracheal instillation, 3-month follow-up) and associated state-of-the-art modelling were undertaken to derive dose coefficients for model tritiated steel particles. A committed effective dose coefficient for the inhalation of 3.3 × 10-12 Sv Bq-1 was evaluated for the particles, reflecting an activity median aerodynamic diameter (AMAD) of 13.3 µm, with the value for a reference AMAD for workers (5 µm) of 5.6 × 10-12 Sv Bq-1 that may be applied to occupational inhalation exposure to tritiated steel particles.

A review of radiation doses and associated parameters in Western Australian mining operations (2018-20).

In the 2019-20 reporting period, 19 mining operations in Western Australia were identified as having workers who were likely to be exposed to ionising radiation stemming from naturally occurring radioactive materials, 17 of which, known hereinafter as reporting entities (REs), were required to submit an annual report of the dose estimates of their workforce to the mining regulatory authority. In 2018 the International Commission for Radiological Protection published the revision of the dose coefficients (DCs) for occupational intakes of radionuclides of the uranium-238 and thorium-232 decay series, in ICRP-137 and ICRP-141. The 2019-20 annual reports are the first to apply the revised DCs to estimate worker doses. The mean effective dose (ED) reported by the 17 REs increased by 32.4% to 0.94 mSv in 2019-20 from 0.71 mSv reported in 2018-19, indicating that the mean ED is approaching the 1 mSv annual dose estimate at which regulatory intervention should be considered. The mean committed effective dose (CED) from inhalation of dusts containing long-lived alpha-emitting (LLα) nuclides has increased by 35% from 0.40 mSv in 2018-19 to 0.54 mSv in 2019-20. The maximum CED from LLαincreased by 16.3% from 3.20 mSv in 2018-19 to 3.72 mSv in 2019-20. The authors consider that, in the absence of other explanations provided by the REs, the increase is largely attributable to the revised DC's published in ICRP-137 and ICRP-141, but highlight that there are significant variations between REs that make a generalised conclusion problematic. The maximum reported ED in 2019-20 was 6.0 mSv, an increase of 36.4% from 2018 to 2019 (4.4 mSv). The 2019-20 reporting period is the first time in a decade in which mine worker EDs have been elevated to the point that EDs have exceeded 5 mSv, a level at which personal monitoring and additional institutional controls are required.

Skin dose contamination conversion coefficients. Benchmark with three simulation codes.

Handling of radioactive material by operators can lead to contamination at the surface of the skin in case of an accident. The quantification of the dose received by the skin due to a contamination scenario is performed by means of dedicated dose coefficients as it is the case for other radiation protection dose quantities described in the literature. However, most available coefficients do not match realistic scenarios according to state-of-the-art of science and technology. Therefore, this work deals with dedicated dose conversion factors for skin contamination. Since there is an increasing demand on dose coefficients in general, these specific coefficients can be used for various calculations in radiation protection. In this work a method to evaluate such coefficients for the skin contamination dose related to photons, electrons, positrons, alpha and neutron particles is proposed. The coefficients are generated using Monte-Carlo simulations with three well established calculation codes (FLUKA, MCNP, and GEANT4). The results of the various codes are compared against each other for benchmarking purposes. The new dose coefficients allow the computation of the skin received dose, in the case of skin contamination scenario of an individual, taking into account the decay radiation of the radionuclides of interest. To benchmark the quantity derived here, comparisons of radionuclide contamination doses to the skin using the VARSKIN code available in the literature are performed with the results of this work.

Establishment and Application of dose evaluation model for typical mammal in dry region in China / 中华放射医学与防护杂志

Objective:To establish a simplified anatomical model with the selected rabbits widely distributed in China′s dry region as the reference species and compare the result of internal exposure dose coefficients based on the present mode and ERICA.Methods:A simplified anatomical model based on anatomy and geometry was established for rabbits. Combined with Monte Carlo program, the deposited energy of radionuclide particles in rabbit tissues/organs was obtained, and the internal and external exposure dose coefficient for rabbits was calculated following the empirical formula.Results:Simplified anatomy model-based dose coefficients were 129I 4.81 × 10 -6, 137Cs 4.34 × 10 -5, and 134Cs 3.81 × 10 -5(μGy·h -1)/(Bq·kg -1) for internal exposure and 129I 3.16 × 10 -7, 137Cs 2.39 × 10 -4 and 134Cs 6.22 × 10 -4(μGy·h -1)/(Bq· kg -1) for external exposure. respectively. ERICA-based dose coefficients were 129I 4.44 × 10 -5, 137Cs 1.94 × 10 -4 and 134Cs 2.34 × 10 -4(μGy·h -1)/(Bq·kg -1) for internal exposure and 129I 2.19 × 10 -6, 137Cs 2.52 × 10 -4 and 134Cs 6.95 × 10 -4(μGy·h -1)/(Bq·kg -1) for external exposure, respectively. Conclusions:The simplified anatomical model established is based on the measured data and focuses on the radiation doses to biological tissues/organs, and the calculated result based on the present model are closer to the actual situation, and can provide reference values for the reference biological evaluation of non-human species.

Monte Carlo determination of dose coefficients at different developmental stages of zebrafish (Danio rerio) in experimental condition.

The release of liquid effluent of nuclear power into aquatic system increases with the rapid development of nuclear facilities in coastal and inland regions. Aquatic model animals are very important for the study of the radiation hazards to non-human biota in water environment and its extrapolation of dose-effect relationship to human models. However, the study of the radiation dose rate calculation model of the aquatic animal zebrafish is still on the homogeneous isotropic model used for the protection of the environment. A series of zebrafish models (including adults, larvae and embryos, named zebrafish-family: ZF-family) with multiple internal organs are established in this study to investigate the mechanism of radiation damage effect in order to protect non-human species. The internal and external dose coefficients (DCs) of the whole body, heart and gonads of zebrafishes are calculated in water environment with the combination of the real experimental culture condition, using Monte Carlo application package GATE (Geant4 Application for Emission Tomography) and eight nuclides, i.e., 3H, 14C, 90Sr, 60Co, 110mAg, 134Cs, 137Cs, 131I, which are commonly found in the liquid effluent of nuclear power plants, as the source items, The results show that the level of nuclide γ energy determines the external DCs (DCext), and 90Sr plays the most important role in internal DCs (DCint). The comparison between the external DCs of the heart and gonad and that of the whole body shows that DCs (DCext) of heart and gonad for females are 80% and 43% lower than that of whole body, respectively, while for males, the DCs (DCext) of heart is 44% lower than that of the whole body, and DCs (DCext) of gonad is slightly higher than that of the whole body for most nuclides (up to 25%).The dose of internal radiation makes greater contribution than that of external radiation to pure beta emitter (3H, 14C, 90Sr). This internal DCs of ZF-family model with complex internal structure turns out to demonstrate more sensitive DCs change trend and higher calculation values compared with the internal DCs of the simple ellipsoid model. In this model, the photon emitter with strong penetrating power has higher internal DCs, while the low-energy pure beta nuclide does not alter much. In conclusion, it is vital to carry out refined systematic modeling for model organisms, and the determination of DCs of model organs can promote the evaluation of the radiation effects on non-human species.

Development of detailed pediatric eye models for lens dose calculations.

The International Commission on Radiological Protection (ICRP) recently reduced the dose limit for the eye lens for occupational exposure from 150 mSv yr-1to 20 mSv yr-1, as averaged over defined periods of five years, with no annual dose in a single year exceeding 50 mSv, emphasizing the importance of the accurate estimation of lens dose. In the present study, for more accurate lens dosimetry, detailed eye models were developed for children and adolescents (newborns and 1, 5, 10, and 15 year olds), which were then incorporated into the pediatric mesh-type reference computational phantoms (MRCPs) and used to calculate lens dose coefficients (DCs) for photon and electron exposures. Finally, the calculated values were compared with those calculated with the adult MRCPs in order to determine the age dependence of the lens DCs. For photon exposures, the lens DCs of the pediatric MRCPs showed some sizable differences from those of the adult MRCPs at very low energies (10 and 15 keV), but the differences were all less than 35%, except for the posterior-anterior irradiation geometry, for which the lens dose is not of primary concern. For electron exposures, much larger differences were found. For the anterior-posterior (AP) and isotropic irradiation geometries, the largest differences between the lens DCs of the pediatric and adult phantoms were found in the energy range of 0.6-1 MeV, where the newborn lens DCs were larger by up to a factor of ∼5 than the adult. The lens DCs of the present study, which were calculated for the radiosensitive region of the lens, also were compared with those for the entire lens in the AP irradiation geometry. Our results showed that the DCs of the entire lens were similar to those of the radiosensitive region for 0.02-2 MeV photons and >2 MeV electrons, but that for the other energy ranges, significant differences were noticeable, i.e. 10%-40% for photons and up to a factor of ∼5 for electrons.

Lung cancer risk and effective dose coefficients for radon: UNSCEAR review and ICRP conclusions.

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has provided a detailed and authoritative update of its reviews of the epidemiology and dosimetry of radon and progeny. Lifetime risk of lung cancer calculated using data for several miner cohorts were 2.4-7.5 × 10-4per working level month (WLM) of radon-222 progeny exposure for a mixed male/female population and 3.0-9.6 × 10-4per WLM for a male population. Dosimetric models gave mean values of effective dose coefficients from radon-222 progeny of 12 mSv per WLM for mines, 16 mSv per WLM for indoor workplaces and 11 mSv per WLM for homes. The lifetime risk coefficient used by the International Commission on Radiological Protection (ICRP) is 5 × 10-4per WLM and it has recently recommended an effective dose coefficient for radon-222 and progeny of 3 mSv per mJ h m-3(about 10 mSv per WLM) for most circumstances of exposure. The ICRP risk and dose coefficients are supported by the UNSCEAR review and provide a clear and firm basis for current international advice and standards for protection from radon. Notwithstanding this evidence and the ICRP advice, UNSCEAR will continue to use a lower value of effective dose coefficient of 5.7 mSv per WLM for assessments of population exposures.

Dose conversion coefficients for neutron external exposures with five postures: walking, sitting, bending, kneeling, and squatting.

In a previous study, posture-dependent dose coefficients (DCs) for photon external exposures were calculated using the adult male and female mesh-type reference computational phantoms (MRCPs) of the International Commission on Radiological Protection (ICRP) that had been transformed into five non-standing postures (i.e. walking, sitting, bending, kneeling, and squatting). As an extension, the present study was conducted to establish another DC dataset for external exposures to neutrons by performing Monte Carlo radiation transport simulations with the adult male and female MRCPs in the five non-standing postures. The resulting dataset included the DCs for absorbed doses (i.e., organ/tissue-averaged absorbed doses) delivered to 29 individual organs/tissues, and for effective doses for neutron energies ranging from 10-9 to 104 MeV in six irradiation geometries: antero-posterior (AP), posteroanterior (PA), left-lateral (LLAT), right-lateral (RLAT), rotational (ROT), and isotropic (ISO) geometries. The comparison of DCs for the non-standing MRCPs with those of the standing MRCPs showed significant differences. In the lateral irradiation geometries, for example, the standing MRCPs overestimate the breast DCs of the squatting MRCPs by up to a factor of 4 due to the different arm positions but underestimate the gonad DCs by up to about 17 times due to the different leg positions. The impact of different postures on effective doses was generally less than that on organ doses but still significant; for example, the standing MRCPs overestimate the effective doses of the bending MRCPs only by 20% in the AP geometry at neutron energies less than 50 MeV, but underestimate those of the kneeling MRCPs by up to 40% in the lateral geometries at energies less than 0.1 MeV.

A new analytical method for estimating electron-absorbed fractions in soft-tissue biological volumes.

A new analytical methodology was developed for estimating electron-absorbed fractions in soft-tissue biological volumes from mono-energy emitters, uniformly distributed within these volumes. The approach was originally developed for soft-tissue spheres and was extended to ellipsoids. The method involves a procedure of size rescaling to the electron CSDA ranges. The rescaling was applied to large published datasets of electron-absorbed fractions in soft-tissue spheres. A new effect was demonstrated, i.e., that it is possible to describe the rescaled data on absorbed fractions by a single smooth 'universal curve'. A simple analytical formula is suggested, which describes the curve as a function of a single argument (the so-called rescaled radius) with saturation. Practical application of the method for estimating internal doses to non-human biota was demonstrated. It is concluded that the method provides an effective analytical tool for calculating the electron-absorbed fractions in soft-tissue bio-volumes relevant to various organisms and organs.

Establishment and application of typical insect dose model in northwestern China / 中华放射医学与防护杂志

Objective:To validate the feasibility of establishing a dosimetric model for insect species by investigating the ecological environment of an inland site in the northwestern China.Methods:For Damalacore, a simplified anatomical model based on anatomy and geometry and a model based on CT scan sequence image were established to produce a voxel model. In combination with the Monte Carlo particle transport process, the deposited energy of the radionuclides in the insect tissues/organs was obtained. The dose rate from 90Sr and 137Cs to Damalacore was calculated on the basis of empirical formula. Results:The dose rate from internal exposure to the simplified anatomical model was 8.58×10 -2for 90Sr and 4.25×10 -3μGy/h for 137Cs, whereas the dose rate from external exposure to the simplified anatomy model was 2.81×10 -2for 90Sr and 2.56×10 -1μGy/h for 137Cs, respectively. The internal exposure to the voxel model from 90Sr and 137Cs was 3.91×10 -2and 2.91×10 -3μGy/h, whereas the external exposure to the voxel model from 90Sr and 137Cs was 2.81×10 -2 and 2.56×10 -1μGy/h, respectively. The internal exposure from 90Sr and 137Cs to ERICA model was 1.46×10 -1 and 1.46×10 -2μGy/h, whereas the external exposure to the ERICA model from 90Sr and 137Cs was 5.79×10 -2 and 2.58×10 -1μGy/h, respectively. Conclusions:The calculated results based on the two models are similar to those based on ERICA model and therefore are proved reliable. With improved model accuracy, the calculated result are more close to the practical situation and feasible.

Effective dose from radiation exposure in medicine: Past, present, and future.

Effective dose (E) has been developed by the International Commission on Radiological Protection (ICRP) as a dose quantity with a link to risks of health detriment, mainly cancer. It is based on reference phantoms representing average individuals, but this is often forgotten in its application to medical exposures, for which its use sometimes goes beyond the intended purpose. There has been much debate about issues involved in the use of E in medicine and ICRP is preparing a publication with more information on this application. This article aims to describe the development of E and explain how it should be used in medicine. It discusses some of the issues that arise when E is applied to medical exposures and provides information on how its use might evolve in the future. The article concludes with responses to some frequently asked questions about uses of E that are in line with the forthcoming ICRP publication. The main use of E in medicine is in meaningful comparison of doses from different types of procedure not possible with measurable dose quantities. However, it can be used, with appropriate care, as a measure of possible cancer risks. When considering E to individual patients, it is important to note that the dose received will differ from that assessed for reference phantoms, and the risk per Sv is likely to be greater on average in children and less in older adults. Newer techniques allow the calculation of patient-specific E which should be distinguished from the reference quantity.

Impacts of revised dose coefficients for the inhalation of NORM-containing dusts encountered in the Western Australian Mining Industry.

The aim of this paper is to evaluate the impact of recent revisions to the dose coefficients published in ICRP-137 and ICRP-141 for members of the232Th,238U and235U decay series on radiation doses received by Western Australian mine workers via the inhalation of insoluble dusts containing long-lived alpha particle emitting radionuclides.Whilst some dose coefficients for individual members of the decay series have decreased, the nett effect is that the sum of all dose coefficients in all three decay series have increased as a result of the revisions. The increase is inversely related to Activity Median Aerodynamic Diameter.Assuming the radionuclides in the inhaled dusts are in secular equilibrium, the dose conversion factors (the mean committed effective dose per unit intake of alpha activity) will increase by a factor between 1.9 and 2.9 times.In 2019, 11 mining operations in Western Australia submitted an annual report of worker radiation exposures to the regulatory authority. The reports indicate that between 35% and 60% of the committed effective doses to workers arises from inhalation of insoluble radioactive dusts. Applying an AMAD of 5 µm and a232Th decay series to238+235U decay series ratio of 10:1, committed effective doses to the workforce are greater by a factor of between 0.74 and 1.26 times from those reported in 2018-19 as a result of the revised DCs published in ICRP-137 and ICRP-141.Guidance on how to calculate doses from the inhalation of radioactive dusts is provided in the regulatory authority's Guideline 'NORM-5: Dose Assessment', which will need revision to incorporate the revised dose coefficients. The Guideline has been widely distributed outside of Western Australia, and those jurisdictions which have adopted all, or sections of it, into their legal framework for radiation protection may need to consider the impact of the revision.

A review of radiation doses and associated parameters in Western Australian mining operations that process ores containing naturally occurring radionuclides for 2018-19.

Naturally occurring radionuclides (NORs) are encountered in varying concentrations in a wide range of commodities that are mined and processed in Western Australia (WA), including mineral sands, coal, phosphate ores, sandblasting materials, and the production of bauxite, titanium dioxide pigment, copper, zinc, lead, tin, tantalum and the refining of zircon.Because they have the potential for workers to receive annual doses in excess of 1 mSv, 14 mining operations in WA are required to submit an annual report of worker doses to the regulatory authority. This research provides a summary of the workforce demographics and radiation doses reported by mining operations for the 2018-19 reporting period in order to establish a benchmark against which to compare future worker exposures. The 2018-19 data is compared to that presented in the last peer-reviewed research, published in 1994 in order to evaluate changes in worker dose profiles over the intervening period.In 1992-93, the collective effective dose received by 1496 workers across seven mining operations was 2824 man.mSv, whereas in 2018-19 it had decreased to 784 man.mSv for 1474 workers in 13 operations. The maximum committed effective dose (CED) decreased by 76%, from 18 mSv (36% of the annual limit) in 1992-93 to 4.4 mSv (22% of the derived annual limit) in 2018-19. The mean CED decreased by 49%, from 1.8 mSv in 1992-93 to 0.97 mSv in 2018-19.As a result of revised DC's published in ICRP-137 and ICRP-141, the impacts upon the mean CED per unit intake of alpha activity arising from inhalation of insoluble NORs-containing dusts, and contribution to CED from inhalation of radon, thoron and their progeny will require evaluation for individual mining operations in the WA mining industry.

Patient-specific anatomical models for radioiodine dosimetry in treatment of hyperthyroidism: is it necessary?

PURPOSE: To investigate the necessity of patient-specific dosimetry calculations using individualized models for hyperthyroid patients treated with radioactive iodine (RAI). This treatment modality was considered to be safe and effective; however, a recent publication indicated associations between greater organ-absorbed doses of RAI and risk of cancer death. METHODS: Ten patient-specific models which ranged in size were used (from 152.5 to 184 cm in height and from 44 to 88 kg in mass). The time-integrated activity coefficients (TIAC) were evaluated from the 2017 Leggett's model assuming 24 h radioactive iodine uptakes (RAIU) of 30, 50, 70, and 90% and two intake routes for normal uptake (ingestion and injection). A set of 131 I S factors (mGy MBq-1  h-1 ) from the patient-specific phantoms including 12 source regions were provided in this study. These S factors were used together with the new TIACs to present dose coefficients. RESULTS: The MC-based patient-specific S factors were compared with the ICRP standard data and the variation ranges (%) of (-65, +210) and (-57, +193) were reported for self and cross S factors, respectively. However, for self S factors, those intervals were reduced to (-8.3, +4.6) when mass correction was applied. Moreover, variations on organ dose coefficients were evaluated and the thyroid contributions were also assessed for 24 h RAIU of 30, 50, 70, and 90%. Considering that the thyroid contribution to adjacent normal organs is high and the variations on cross dose coefficients are also considerable, variations (%) on normal organ doses were estimated to be up to (-63, +132), with a planned thyroid absorbed dose of 150 Gy. CONCLUSION: Given the large variations on organ doses, the standard data are not an appropriate substitute for patient-specific data. Particularly, when accurate patient-specific dose estimation is a serious concern in RAI treatment (RAIT) for nuclear medicine practitioners. However, acquiring computed tomography (CT) images for patient-specific modeling will impose additional radiation dose to patients. It was concluded that CT imaging limited to the region from skull base to mid thorax (i.e., for organs with RAIT doses of >~50 mGy with a dose of 150 Gy prescribed to the thyroid) may be suggested and is clinically relevant because the normal organ dose increments are not greater than 10%.

ICRP recommendations on radon.

The International Commission on Radiological Protection (ICRP) publishes guidance on protection from radon in homes and workplaces, and dose coefficients for use in assessments of exposure for protection purposes. ICRP Publication 126 recommends an upper reference level for exposures in homes and workplaces of 300 Bq m-3. In general, protection can be optimised using measurements of air concentrations directly, without considering radiation doses. However, dose estimates are required for workers when radon is considered as an occupational exposure (e.g. in mines), and for higher exposures in other workplaces (e.g. offices) when the reference level is exceeded persistently. ICRP Publication 137 recommends a dose coefficient of 3 mSv per mJ h m-3 (approximately 10 mSv per working level month) for most circumstances of exposure in workplaces, equivalent to 6.7 nSv per Bq h m-3 using an equilibrium factor of 0.4. Using this dose coefficient, annual exposure of workers to 300 Bq m-3 corresponds to 4 mSv. For comparison, using the same coefficient for exposures in homes, 300 Bq m-3 corresponds to 14 mSv. If circumstances of occupational exposure warrant more detailed consideration and reliable alternative data are available, site-specific doses can be assessed using methodology provided in ICRP Publication 137.