Radiation Protection Purposes Research Articles

High energy photon reference for radiation protection: technical design of the LINAC beam and ionization chambers; and calculation of monoenergetic conversion coefficients

In this work, we present the results of the first part of a research project aimed at offering a complete response to dosimeters providers and nuclear physicists’ demands for high-energy (6 – 9 MeV) photon beams for radiation protection purposes. Classical facilities allowing the production of high-energy photonic radiation (proton accelerators, nuclear reactors) are very rare and need large investment for development and use. A novel solution is proposed, consisting in the use of a medical linear accelerator, allowing a significant decrease of all costs.Using Monte Carlo simulations (MCNP5 and PENELOPE codes), a specifically designed electron-photon conversion target allowing for obtaining a high energy photon beam (with an average energy weighted by fluence of about 6 MeV) has been built for radiation protection purposes. Due to the specific design of the target, this “realistic” radiation protection high-energy photon beam presents a uniform distribution of air kerma rate at a distance of 1 m, over a 30 × 30 cm2 surface. Two graphite cavity ionizing chambers for ionometric measurements have been built. For one of these chambers, the charge collection volume has been measured allowing for its use as a primary standard. The second ionizing chamber is used as a transfer standard; as such it has been calibrated in a 60Co beam, and in the high energy photon beam for radiation protection.The measurements with these ionizing chambers allowed for an evaluation of the air kerma rate in the LINAC based high-energy photon beam for radiation protection: the values cover a range between 36 mGy/h and 210 mGy/h, compatible with radiation protection purposes.Finally, using Monte Carlo simulations, conversion coefficients from air kerma to dose equivalent quantities have been calculated in the range between 10 keV and 22.4 MeV, for the spectral distribution of the fluence corresponding to the beam produced by the linear accelerator of the LNE-LNHB.

Global Gene Expression Alterations as a Crucial Constituent of Human Cell Response to Low Doses of Ionizing Radiation Exposure

Exposure to ionizing radiation (IR) is inevitable to humans in real-life scenarios; the hazards of IR primarily stem from its mutagenic, carcinogenic, and cell killing ability. For many decades, extensive research has been conducted on the human cell responses to IR delivered at a low dose/low dose (LD) rate. These studies have shown that the molecular-, cellular-, and tissue-level responses are different after low doses of IR (LDIR) compared to those observed after a short-term high-dose IR exposure (HDIR). With the advent of high-throughput technologies in the late 1990s, such as DNA microarrays, changes in gene expression have also been found to be ubiquitous after LDIR. Very limited subset of genes has been shown to be consistently up-regulated by LDIR, including CDKN1A. Further research on the biological effects and mechanisms induced by IR in human cells demonstrated that the molecular and cellular processes, including transcriptional alterations, activated by LDIR are often related to protective responses and, sometimes, hormesis. Following LDIR, some distinct responses were observed, these included bystander effects, and adaptive responses. Changes in gene expression, not only at the level of mRNA, but also miRNA, have been found to crucially underlie these effects having implications for radiation protection purposes.

A new method to evaluate the residual activity in patients undergoing 131I thyroid therapy

The radioiodine administration is a standard therapeutic approach to both benign thyroid diseases, such as hyperthyroidism, and carcinomas. The high administered 131I activities are of radiation protection concern, due to relevant patient residual contamination. The aim of this work was to develop a new procedure based on external radiometric surveys and on a mathematical model in order to estimate the 131I activity in patients undergoing hyperthyroidism radioiodine therapy.In the first stage of this study, a suitable detector was chosen and its response vs. activity was characterized. The experimental verification was performed measuring the ambient dose equivalent rate from patients receiving radioiodine administration. The results confirm the reliability of the proposed method, as shown by the slight differences between the administered activities and the ones calculated from external measurements. Furthermore, the same procedure was applied to detect the percentage residual activity in patients at two preset time intervals: 4 hours and 4 days after the radioiodine administration. The obtained results clearly highlight that the method can ensure a level of reliability compatible with the radiation protection purposes.

ON-FIELD EVALUATION OF OPERATOR LENS PROTECTIVE DEVICES IN INTERVENTIONAL RADIOLOGY.

The recent publication of the Euratom Directive 2013/59, adopting the reduction of eye lens dose limits from 150 to 20 mSv y-1, calls for the development of new tools and methodologies for evaluating the eye lens dose absorbed by the medical staff involved in interventional radiology practices. Moreover, the effectiveness of the protective devices, like leaded glasses, which can be employed for radiation protection purposes, must be tested under typical exposure scenarios. In this work, eye lens dose measurements were carried out on an anthropomorphic phantom simulating a physician bound to perform standard interventional neuroradiology angiographic procedures. The correlation between eye lens doses, in terms of Hp(0.07), and the equivalent dose [again in terms of Hp(0.07)] monthly measured with thermoluminescent dosemeters placed above the lead apron at the chest level was studied, in the presence and in the absence of different types of leaded glasses.

The EURALOC Project

SummaryFor radiation protection purposes, it has generally been assumed that there is a threshold of dose below which no non‐cancer effects arise. Early dose threshold estimates for detectable lens opacities were defined at 0.5–2 Gy after acute or 5–6 Gy after protracted exposures. Due to the heterogeneity of ophthalmological data and too short observation periods, the thresholds were reconsidered in the ICRP report 118 (2012) and reduced to 0.5 Gy. An overview will be given of epidemiological studies that prompted the change in ICRP recommendations. These studies reported excess risks of lens opacities, but could not provide statistical significant evidence of a dose threshold. The results from all these studies are difficult to compare or combine. Moreover, another point of concern is the dosimetry which was often poor. These issues limit the possibility of a quantitative synthesis of evidence for a dose‐response analysis in the low dose region to confirm this new dose threshold and urged the need of a harmonised European initiative. The EURALOC project, initiated in December 2014, aims at quantifying this dose‐response relationship between ionising radiation and cataract among a cohort of European interventional cardiologists.

A SOLUTION FOR NEUTRON PERSONAL DOSIMETRY IN THE ABSENCE OF WORKPLACE SPECTROMETRY.

In view of the widely varying energy spectra encountered in practical situations, accuracy of neutron dose assessment requires detailed knowledge of detector responses and workplace conditions to achieve an adequate level of protection. If the neutron spectrum should be a priori unknown and no measurement of the workplace spectrum is available, the 'Compendium of Neutron Spectra and Detector Responses for Radiation Protection Purposes' published in the International Atomic Energy Agency Technical Report Series offers a broad range of reference spectra that may be appropriate for many applications. The proposed approach applies a correction factor based on the ratio of 'personal dose equivalent indices' for a particular workplace spectrum and a reference field used for calibration of the dosemeter response. Amendments in the definition of operational quantities as well as introduction of new modalities that, for example, may be expected to give increased importance to high-energy neutrons necessitate frequent revision of the Compendium. Results from the European Radiation Dosimetry Group Intercomparison 2012 for neutron personal dosemeters provide evidence that workplace fields are insufficiently reflected. This is proposed to be considered as an improvement opportunity.

P.18 - Monitoring radiation exposure levels among nursing staff working in theatre at Dr George Mukhari Academic Hospital

Introduction: Orthopaedic surgeons and radiographers working in theatre at the Dr George Mukhari Academic Hospital are issued with radiation monitoring dosimeters for radiation protection purposes. However the nursing staff, who work closely with orthopaedic surgeons during fluoroscopy procedures, are not issued with the radiation monitoring badges. The aim of this study was to determine whether the nursing personnel working in theatre do receive an effective dose greater than 30% of the legislated occupational annual dose limit.

Monte Carlo simulations of the secondary neutron ambient and effective dose equivalent rates from surface to suborbital altitudes and low Earth orbit

Occupational exposures from ionizing radiation are currently regulated for airline travel (<20 km) and for missions to low-Earth orbit (∼300–400 km). Aircrew typically receive between 1 and 6 mSv of occupational dose annually, while aboard the International Space Station, the area radiation dose equivalent measured over just 168 days was 106 mSv at solar minimum conditions. It is anticipated that space tourism vehicles will reach suborbital altitudes of approximately 100 km and, therefore, the annual occupational dose to flight crew during repeated transits is expected to fall somewhere between those observed for aircrew and astronauts. Unfortunately, measurements of the radiation environment at the high altitudes reached by suborbital vehicles are sparse, and modelling efforts have been similarly limited. In this paper, preliminary MCNPX radiation transport code simulations are developed of the secondary neutron flux profile in air from surface altitudes up to low Earth orbit at solar minimum conditions and excluding the effects of spacecraft shielding. These secondary neutrons are produced by galactic cosmic radiation interacting with Earth's atmosphere and are among the sources of radiation that can pose a health risk. Associated estimates of the operational neutron ambient dose equivalent, used for radiation protection purposes, and the neutron effective dose equivalent that is typically used for estimates of stochastic health risks, are provided in air. Simulations show that the neutron radiation dose rates received at suborbital altitudes are comparable to those experienced by aircrew flying at 7 to 14 km. We also show that the total neutron dose rate tails off beyond the Pfotzer maximum on ascension from surface up to low Earth orbit.

Analyses of local dose distributions in the lungs for the determination of risk apportionment factors.

For radiation protection purposes, the relative contributions of bronchial (BB), bronchiolar (bb) and alveolar-interstitial (AI) doses to lung cancer risk are represented by their corresponding apportionment factors. The current assumption of equal apportionment factors can be tested by comparing different radon and thoron progeny exposures, which produce different regional dose distributions, with the pathologically observed regional cancer distributions: (1) radon progeny inhalation, (2) thoron progeny inhalation, (3) thoron and thoron progeny exhalation (Thorotrast patients) and (4) RP inhalation in rats, and cigarette smoke inhalation as smoking is the dominant cause of lung cancer. Comparison with the pathologically observed regional cancer distributions suggests (1) a smaller apportionment factor for the AI region as compared with BB and bb regions and (2) a higher value for the BB region relative to that for the bb region.

Measuring scatter radiation in diagnostic X rays for radiation protection purposes.

During the last decades, radiation protection and dosimetry in medical X-ray imaging practice has been extensively studied. The purpose of this study was to measure secondary radiation in a conventional radiographic room, in terms of ambient dose rate equivalent H*(10) and its dependence on the radiographic exposure parameters such as X-ray tube voltage, tube current and distance. With some exceptions, the results indicated that the scattered radiation was uniform in the space around the water cylindrical phantom. The results also showed that the tube voltage and filtration affect the dose rate due to the scatter radiation. Finally, the scattered X-ray energy distribution was experimentally calculated.

Implications of X-ray tube parameter deviations in X-ray reference fields.

For the purpose of radiation protection, ICRU Report 57/ICRP Publication 74 provides a list of monoenergetic conversion coefficients to be used with, among others, photon reference fields generated with X-ray tubes. A comprehensive definition of these photon reference fields can be found in international standard ISO 4037; however, it lacks thorough indication of the allowed deviations of essential parameters that influence these X-ray reference fields. These parameters are the high-voltage tube potential, the thickness of the beryllium window and the purity and thickness of the filter materials used to create different radiation qualities. Small variations of these parameters can lead to significant changes in the created X-ray spectra and, hence, the spectra-dependent conversion coefficients for phantom-related radiation-protection quantities. This can lead to situations in which the conversion coefficients listed in ISO 4037 cannot be used, resulting in time-consuming spectrometry measurements. In this work, the impact on the resulting conversion coefficients is investigated using a simplified mathematical approximation model. The findings are validated with an independent X-ray spectra calculation programme. As a result, well-founded upper limit values on the allowed deviations of the essential X-ray tube parameters are proposed to be used in a future revision of ISO 4037.

Reaction mechanism interplay in determining the biological effectiveness of neutrons as a function of energy

Neutron relative biological effectiveness (RBE) is found to be energy dependent, being maximal for energies ∼1 MeV. This is reflected in the choice of radiation weighting factors wR for radiation protection purposes. In order to trace back the physical origin of this behaviour, a detailed study of energy deposition processes with their full dependences is necessary. In this work, the Monte Carlo transport code PHITS was used to characterise main secondary products responsible for energy deposition in a 'human-sized' soft tissue spherical phantom, irradiated by monoenergetic neutrons with energies around the maximal RBE/wR. Thereafter, results on the microdosimetric characterisation of secondary protons were used as an input to track structure calculations performed with PARTRAC, thus evaluating the corresponding DNA damage induction. Within the proposed simplified approach, evidence is suggested for a relevant role of secondary protons in inducing the maximal biological effectiveness for 1 MeV neutrons.

Evaluation of the Response of Tritium-In-Air Instrumentation to HT in Dry and Humid Conditions and to HTO Vapor

Nuclear plant operators (power generation, decommissioning and reprocessing operations) are required to monitor releases of tritium species for regulatory compliance and radiation protection purposes. Tritium monitoring is performed using tritium-in-air gas monitoring instrumentation based either on flow-through ion chambers or proportional counting systems. Tritium-in-air monitors are typically calibrated in dry conditions but in service may operate at elevated levels of relative humidity. The NPL radioactive gas-in-air calibration system has been used to study the effect of humidity on the response to tritium of two tritium-in-air ion chamber based monitors and one proportional counting system which uses a P10/air gas mixture. The response of these instruments to HTO vapour has also been evaluated. In each case, instrument responses were obtained for HT in dry conditions (RH ~2%), HT in 45% Relative Humidity (RH), and finally HTO at 45% RH. Instrumentation response to HT in humid conditions has been found to slightly exceed that in dry conditions.

Reconstruction of head-to-knee voxel model for Syrian adult male of average height and weight

PurposeThis study embodies the reconstruction of head to knee voxel model, named “SyrMan”, of an adult living Syrian male of average height and weight. This model contains main organs of one adult man representing the average of a group of adult males (25–50) years. SyrMan model was reconstructed to be used for Monte Carlo simulations to calculate dosimetric quantities for radiation protection and medical purposes. MethodThe model was reconstructed from segmented CT images of a living volunteer who was 33year-old, 172cm in height, and 75kg in weight. Masses of segmented organs were calculated and compared with previously published models. ResultsSpecific Absorbed Fractions (SAFs) were calculated and tabulated for each considered source organ. Comparison of SAF values was carried out with Zubal model where some significant differences were found due to differences in organ masses and in anatomy between both models. ConclusionComparisons with SAFs data of Zubal model accentuated the fact that the organ masses and the specific anatomy have a significant effect on SAFs. SyrMan model can be considered as the first model built in the Middle East region, and it is an important step toward the Syrian Reference Man.

Radiation signatures in childhood thyroid cancers after the Chernobyl accident: possible roles of radiation in carcinogenesis.

After the Tokyo Electric Power Company Fukushima Daiichi nuclear power plant accident, cancer risk from low-dose radiation exposure has been deeply concerning. The linear no-threshold model is applied for the purpose of radiation protection, but it is a model based on the concept that ionizing radiation induces stochastic oncogenic alterations in the target cells. As the elucidation of the mechanism of radiation-induced carcinogenesis is indispensable to justify the concept, studies aimed at the determination of molecular changes associated with thyroid cancers among children who suffered effects from the Chernobyl nuclear accident will be overviewed. We intend to discuss whether any radiation signatures are associated with radiation-induced childhood thyroid cancers.

US Transuranium and Uranium Registries case study on accidental exposure to uranium hexafluoride

The United States Transuranium and Uranium Registries’ (USTUR) whole-body donor (Case 1031) was exposed to an acute inhalation of uranium hexafluoride (UF6) produced from an explosion at a uranium processing plant 65 years prior to his death. The USTUR measurements of tissue samples collected at the autopsy indicated long-term retention of inhaled slightly enriched uranium material (0.85% 235U) in the deep lungs and thoracic lymph nodes. In the present study, the authors combined the tissue measurement results with historical bioassay data, and analysed them with International Commission on Radiological Protection (ICRP) respiratory tract models and the ICRP Publication 69 systemic model for uranium using maximum likelihood and Bayesian statistical methods. The purpose of the analysis was to estimate intakes and model parameter values that best describe the data, and evaluate their effect on dose assessment. The maximum likelihood analysis, which used the ICRP Publication 66 human respiratory tract model, resulted in a point estimate of 79 mg of uranium for the occupational intake composed of 86% soluble, type F material and 14% insoluble, type S material. For the Bayesian approach, the authors applied the Markov Chain Monte Carlo method, but this time used the revised human respiratory tract model, which is currently being used by ICRP to calculate new dose coefficients for workers. The Bayesian analysis estimated that the mean uranium intake was 160 mg, and calculated the case-specific lung dissolution parameters with their associated uncertainties. The parameters were consistent with the inhaled uranium material being predominantly soluble with a small but significant insoluble component. The 95% posterior range of the rapid dissolution fraction (the fraction of deposited material that is absorbed to blood rapidly) was 0.12 to 0.91 with a median of 0.37. The remaining fraction was absorbed slowly, with a 95% range of 0.000 22 d−1 to 0.000 36 d−1 and a median of 0.000 31 d−1. The effective dose per unit intake calculated using the dissolution parameters derived from the maximum likelihood and the Bayesian analyses was higher than the current ICRP dose coefficient for type F uranium by a factor of 2 or 7, respectively; the higher value of the latter was due to use of the revised respiratory tract model. The dissolution parameter values obtained here may be more appropriate to use for radiation protection purposes when individuals are exposed to a UF6 mixture that contains an insoluble uranium component.

Removal of lead (II) from aqueous solutions by adsorption onto activated carbons prepared from coconut shell

In the nuclear field, the availability of effective techniques to eliminate lead pollution from wastewater is of interest both for the purposes of radiation protection from the radioactive isotope lead-210 and also for the issues related to the use of lead in the new generation reactors nowadays under study. Evidences exist of lead pollution due to the radioactive isotope lead-210 in the proximities of uranium extraction mines. In this study, two commercial granular activated carbons obtained by physical activation of coconut shell, specifically developed and selected to purify potable water from dissolved organics (GCN 1240) and for use in gold recovery systems (GCN 816 G), were studied in batch systems to evaluate their effectiveness for separation of lead (II) from aqueous solutions. A characterization of the two carbons, different in particle size, is provided through determination of their pHPZC and scanning electron microscope analysis. Adsorption of lead (II) was observed as a function of contact time, and its kinetics were fitted. Adsorption data at equilibrium were fitted by isotherm models and the maximum adsorption capacity of the carbons resulted to be 92.39 mg/g (GCN1240) and 32.08 mg/g (GCN 816 G). Experiments were carried out to investigate effects of pH on lead adsorption, evidencing that best removal performances of lead occur near pH 5.0. The present study shows that the considered commercial granular activated carbons can be successfully adopted for removal of lead (II) by adsorption from aqueous solutions.

Fluence-to-effective dose conversion coefficients from a Saudi population based phantom for monoenergetic photon beams from 10 keV to 20 MeV

Fluence-to-dose conversion coefficients are important quantities for radiation protection, derived from Monte Carlo simulations of the radiation particles through a stylised phantom or voxel based phantoms. The voxel phantoms have been developed for many ethnic groups for their accurate reflection of the anatomy. In this study, we used the Monte Carlo code MCNPX to calculate the photon fluence-to-effective dose conversion coefficients with a voxel phantom based on the Saudi Arabian male population. Six irradiation geometries, anterior–posterior (AP), posterior–anterior (PA), left lateral (LLAT), right lateral (RLAT), rotational (ROT) and isotropic (ISO) were simulated for monoenergetic photon beams from 10 keV to 20 MeV. We compared the coefficients with the reference values in ICRP Publication 116. The coefficients in the AP and PA geometries match the reference values to 9% and 12% on average as measured by root mean square while those in the LLAT, RLAT ROT and ISO geometries differ, mostly below, from the reference by 23, 22, 15 and 16%, respectively. The torso of the Saudi phantom is wider than the ICRP reference male phantom and likely to cause more attenuation to the lateral beam. The ICRP reference coefficients serve well for the Saudi male population as conservative estimations for the purpose of radiation protection.

Current discussions of DDREF, cataracts, circulatory diseases and dose limits.

Although more than a century of radiation research has provided a lot of insight into radiation risk, there are still fields that need clarification. This is particularly true for the low dose range, meaning doses up to ∼100 mSv. One can detect biological effects in that dose range, but it is unclear whether these biological effects like mutations or chromosomal aberrations translate into health effects like cancer, cataracts or circulatory diseases. Thus, for radiation protection purposes, assumptions have to made that must be reappraised on the basis of new findings from time to time. Affected by new insights are currently the DDREF (dose and dose-rate effectiveness factor), cataracts and circulatory diseases. If the new findings are very convincing, dose limits have to be changed at short notice. If there are only weak indications, stability of the radiation protection system is more important than changing limits all the time.

Spectral correction factors for conventional neutron dosemeters used in high-energy neutron environments.

High-energy neutrons (>10 MeV) contribute substantially to the dose fraction but result in only a small or negligible response in most conventional moderated-type neutron detectors. Neutron dosemeters used for radiation protection purpose are commonly calibrated with (252)Cf neutron sources and are used in various workplace. A workplace-specific correction factor is suggested. In this study, the effect of the neutron spectrum on the accuracy of dose measurements was investigated. A set of neutron spectra representing various neutron environments was selected to study the dose responses of a series of Bonner spheres, including standard and extended-range spheres. By comparing (252)Cf-calibrated dose responses with reference values based on fluence-to-dose conversion coefficients, this paper presents recommendations for neutron field characterisation and appropriate correction factors for responses of conventional neutron dosemeters used in environments with high-energy neutrons. The correction depends on the estimated percentage of high-energy neutrons in the spectrum or the ratio between the measured responses of two Bonner spheres (the 4P6_8 extended-range sphere versus the 6″ standard sphere).