Radiation doses and risks from internal emitters

Parameter uncertainty analysis of the equivalent lung dose coefficient for the intake of radon in mines: A review

Radon presents significant health risks due to its short-lived progeny. The evaluation of the equivalent lung dose coefficient is crucial for assessing the potential health effects of radon exposure. This review focuses on the uncertainty analysis of the parameters associated with the calculation of the equivalent lung dose coefficient attributed to radon inhalation in mines. This analysis is complex due to various factors, such as geological conditions, ventilation rates, and occupational practices. The literature review systematically examines the sources of radon and its health effects among underground miners. It also discusses the human respiratory tract model used to calculate the equivalent lung dose coefficient and the associated parameters leading to uncertainties in the calculated lung dose. Additionally, the review covers the different methodologies employed for uncertainty quantification and their implications on dose assessment. The text discusses challenges and limitations in current research practices and provides recommendations for future studies. Accurate risk assessment and effective safety measures in mining environments require understanding and mitigating parameter uncertainties.

Health risks from radioactive particles on Cumbrian beaches near the Sellafield nuclear site

A monitoring programme, in place since 2006, continues to recover radioactive particles (<2 mm diameter) and larger objects from the beaches of West Cumbria. The potential risks to members of the public using the beaches are mainly related to prolonged skin contact with or the inadvertent ingestion of small particles. Most particles are classified as either 'beta-rich' or 'alpha-rich' and are detected as a result of their caesium-137 or americium-241 content. Beta-rich particles generally also contain strontium-90, with90Sr:137Cs ratios of up to about 1:1, but typically <0.1:1. Alpha-rich particles contain plutonium isotopes, with Pu:241Amαratios usually around 0.5-0.6:1. 'Beta-rich' particles have the greatest potential to cause localised skin damage if held in stationary contact with the skin for prolonged periods. However, it is concluded that only particles of >106Bq of137Cs, with high90Sr:137Cs ratios, would pose a significant risk of causing acute skin ulceration. No particles of this level of activity have been found. Inadvertent ingestion of a particle will result in the absorption to blood of a small proportion of the radionuclide content of the particle. The subsequent retention of radionuclides in body organs and tissues presents a potential risk of the development of cancer. For 'beta-rich' particles with typical activities (mean 2 × 104Bq137Cs, Sr:Cs ratio of 0.1:1), the estimated committed effective doses are about 30µSv for adults and about 40µSv for 1 year old infants, with lower values for 'alpha-rich' particles of typical activities. The corresponding estimates of lifetime cancer incidence following ingestion for both particle types are of the order of 10-6for adults and up to 10-5for infants. These estimates are subject to substantial uncertainties but provide an indication of the low risks to members of the public.

ESTIMATION OF PATIENT ORGAN AND WHOLE-BODY DOSES IN [18F-FDG] PET/CT SCAN

The object of this study was to estimate organ doses and whole-body effective doses from positron emission tomography/computed tomography (PET/CT) scan using [fluorine-18]-fluoro-2-deoxy-d-glucose (18F-FDG) in adult patients and to assess the CT component contribution to organ and whole-body doses. The [18F-FDG] PET/CT scan was conducted on 204 adult patients (90 females and 114 males). For all patients, females and males, the whole-body effective doses were 20.54, 23.89 and 17.89 mSv, respectively. For all patients, females and males, the CT component contribution to the whole-body effective dose was 66, 71 and 62%, respectively. Since CT is the primary contributor to the effective dose in the [18F-FDG] PET/CT scan protocol, the significance of improving CT protocols to minimize patient dose is underscored. All attempts must be made, using available mechanisms and techniques, to reduce the patient's dose of PET/CT scan, especially in obese patients.

The Preparation, Biodistribution, and Dosimetry of Encapsulated Radio-Scandium in a Dendrimer for Radio-nano-pharmaceutical Application

This study aimed to investigate the synthesis, characterization, and biodistribution of scandium nanoparticles encapsulated within poly (amidoamine) (PAMAM) dendrimers, as well as to estimate the human absorbed dose. It also aimed to examine, in particular, the amine-terminated PAMAM dendrimers in generation 5. Irradiation of the compound in the nuclear reactor resulted in the formation of Sc-radioactive complex nanoparticles. The compound of the dendrimer-Sc³⁺ was confirmed by the UV-vis spectrometer. The size of the particles was less than 10 nm, and it was assessed using high-resolution transmission electron microscopy (HRTEM) and dynamic light scattering (DLS). The synthesized complex was irradiated by the 3 × 10¹¹ n.cm^-2s^-1 flux of neutron for 2 h. Mice bearing a breast tumor were employed to assess the therapeutic dose that was delivered by the poly scandium-46-nanoparticles. As opposed to the untreated groups, a single injection of poly phosphate-buffered saline to intratumoral in other groups to deliver a dose of 100 µCi resulted in a statistically significant 39.24% reduction in tumor volume 14 days after injection. After applying the biokinetics data in mice, the human’s absorbed dose from scandium-47 encapsulated PAMAM was extrapolated based on animal data. The absorbed doses in critical organs, including the liver, lung, spleen, kidney, and bone, were 0.879, 0.0472, 0.191, 0.107, and 0.155 mGy/MBq, respectively.

Navigation and non-navigation CT scan of the sinuses: comparison of the effective doses of radiation in children and adults

BACKGROUND

The advent of 3D navigation imaging has opened new borders to the endoscopic surgical approaches of naso-sinusal inflammatory and neoplastic disease. This technology has gained in popularity among otolaryngologists for endoscopic sinus and skull base surgeries in both adults and children. However, the increased tissue radiation required for data acquisition associated with 3D navigation protocols CT scans is a source of concern because of its potential health hazards. We aimed to compare the effective doses of radiation between 3D navigation protocols and standard protocols for sinus computed tomography (CT) scans for both the adult and pediatric population.

METHODS

We performed a retrospective cohort study through electronic chart review of patients undergoing sinus CT scans (standard and 3D navigation protocols) from May 2019 to December 2019 using a Siemens Drive (VA62A) CT scanner. The effective dose of radiation was calculated in mSv for all exams. Average irradiation doses were compared using a Student's T-Test or a Kruskall-Wallis test when appropriate.

RESULTS

A total of 115 CT scans were selected for analysis, of which 47 were standard protocols and 68 were 3D navigation protocols CT scans. Among these, 31 exams were performed on children and 84 exams on adults. For the total population, mean effective dose in the non-navigation CT scans was 0.37 mSv (SD: 0.16, N = 47) and mean effective dose in the 3D navigation sinus CT group was 2.33 mSv (SD: 0.45, N = 68). The mean difference between the two groups was statistically significant 1.97 mSv (CI 95% - 2.1 to - 1.83; P < 0.0001). There was a sixfold increase in radiation with utilization of 3D navigation protocols. The ratio was identical when the pediatric as well as the adult subset of patients were analyzed.

CONCLUSION

In our center, utilization of 3D navigation sinus CT protocols significantly increases radiation exposure. Otolaryngologists should be aware of this significant increase and should attempt to decrease the radiation exposure of their patients by limiting unnecessary scan orders and by evaluating 3D acquisition protocols locally with radiation physicists.

LEVEL OF EVIDENCE

Level IV.

Treatment of radiological contamination: a review

After nuclear accidents, people can be contaminated internally via ingestion, inhalation and via intact skin or wounds. The assessment of absorbed, committed doses after internal exposure is based on activity measurement byin vivoorin vitrobioassay. Estimation of dose following internal contamination is dependent on understanding the nature and form of the radionuclide. Direct counting methods that directly measureγ-rays coming from within the body or bioassay methods that measure the amount of radioactive materials in urine or feces are used to estimate the intake, which is required for calculating internal exposure doses. The interpretation of these data in terms of intake and the lifetime committed dose requires knowledge or making assumptions about a number of parameters (time, type of exposure, route of the exposure, physical, biological and chemical characteristics) and their biokinetics inside the body. Radioactive materials incorporated into the body emit radiation within the body. Accumulation in some specific organs may occur depending on the types of radioactive materials. Decorporation therapy is that acceleration of the natural rate of elimination of the contaminant will reduce the amount of radioactivity retained in the body. This article presents an overview of treatment of radiological contamination after internal contamination.

Microdosimetric investigation of the radiation quality of low-medium energy electrons using Geant4-DNA

The increasing clinical use of low-energy photon and electron sources (below few tens of keV) has raised concerns on the adequacy of the existing approximation of an energy-independent radiobiological effectiveness. In this work, the variation of the quality factor (Q) and relative biological effectiveness (RBE) of electrons over the low-medium energy range (0.1 keV-1 MeV) is examined using several microdosimetry-based Monte Carlo methodologies with input data obtained from Geant4-DNA track-structure simulations. The sensitivity of the results to the different methodologies, Geant4-DNA physics models, and target sizes is examined. Calculations of Q and RBE are based on the ICRU Report 40 recommendations, the Kellerer-Hahn approximation, the site version of the theory of dual radiation action (TDRA), the microdosimetric kinetic model (MKM) of cell survival, and the calculated yield of DNA double strand breaks (DSB). The stochastic energy deposition spectra needed as input in the above approaches have been calculated for nanometer spherical volumes using the different electron physics models of Geant4-DNA. Results are normalized at 100 keV electrons which is here considered the reference radiation. It is shown that in the energy range ~50 keV-1 MeV, the calculated Q and RBE are approximately unity (to within 1-2%) irrespective of the methodology, Geant4-DNA physics model, and target size. At lower energies, Q and RBE become energy-dependent reaching a maximum value of ~1.5-2.5 between ~200 and 700 eV. The detailed variation of Q and RBE at low energies depends mostly upon the adopted methodology and target size, and less so upon the Geant4-DNA physics model. Overall, the DSB yield predicts the highest RBE values (with RBE_max≈2.5) whereas the MKM the lowest RBE values (with RBE_max≈1.5). The ICRU Report 40, Kellerer-Hahn, and TDRA methods are in excellent agreement (to within 1-2%) over the whole energy range predicting a Q_max≈2. In conclusion, the approximation Q=RBE=1 was found to be valid only above ~50 keV whereas at lower energies both Q and RBE become strongly energy-dependent. It is envisioned that the present work will contribute towards establishing robust methodologies to determine theoretically the energy-dependence of radiation quality of individual electrons which may then be used in subsequent calculations involving practical electron and photon radiation sources.

Uranium Aerosol Activity Size Distributions at a Nuclear Fuel Fabrication Plant

Inhalation of uranium aerosols is a concern in nuclear fuel fabrication. Determination of committed effective doses and lung equivalent doses following inhalation intake requires knowledge about aerosol characteristics; e.g., the activity median aerodynamic diameter (AMAD). Cascade impactor sampling of uranium aerosols in the breathing zone of nuclear operators was carried out at a nuclear fuel fabrication plant producing uranium dioxide via ammonium uranyl carbonate. Complementary static sampling was carried out at key process steps. Uranium on impaction substrates was measured using gross alpha counting and alpha spectrometry. Activity size distributions were evaluated for both unimodal and bimodal distributions. When a unimodal distribution was assumed, the average AMAD in the operator breathing zone at the workshops was 12.9-19.3 μm, which is larger than found in previous studies. Certain sampling occasions showed variable isotope ratios (U/U) at different impactor stages, indicating more than one population of particles; i.e., a multimodal activity size distribution. When a bimodal distribution (coarse and fine fraction) was assumed, 75-88% of the activity was associated with an AMAD of 15.2-18.9 μm (coarse fraction). Quantification of the AMAD of the fine fraction was associated with large uncertainties. Values of 1.7-7.1 μm were obtained. Static sampling at key process steps in the workshops showed AMADs of 4.9-17.2 μm, generally lower than obtained by breathing zone sampling, when a unimodal distribution was assumed. When a bimodal distribution was assumed, a smaller fraction of the activity was associated with the coarse fraction compared to breathing zone sampling. This might be due to impactor positioning during sampling and sedimentation of large particles. The average committed effective dose coefficient for breathing zone sampling and a bimodal distribution was 1.6-2.6 μSv Bq for U when Type M/S absorption parameters were assumed (5.0 μSv Bq for an AMAD of 5 μm). The corresponding lung equivalent dose coefficient was 3.6-10.7 μSv Bq (29.9 μSv Bq for an AMAD of 5 μm). The predicted urinary excretion level 100 d after inhalation intake was found to be 13-34% of that corresponding to an AMAD of 5 μm. Uranium aerosols generated at a nuclear fuel fabrication plant using ammonium uranyl carbonate route of conversion were associated with larger AMADs compared to previous work, especially when sampling of aerosols was carried out in the operator breathing zone. A bimodal activity size distribution can be used in calculations of committed effective doses and lung equivalent doses, but parameters associated with the fine fraction must be interpreted with care due to large uncertainties.

The low dose effects of human mammary epithelial cells induced by internal exposure to low radioactive tritiated water

Tritium is an important radioactive waste which needs to be monitored for radiation protection. Due to long biological half-life of organically bound tritium (OBT), the adverse consequence caused by chronic exposure of tritiated water (HTO) attracts concern. In this study, fibroblast cells were exposed to 2 × 10⁶ Bq/ml HTO to investigate the cellular behaviors. The dose relationship of survival fraction and γH2AX foci was a "U-shaped" curve. And the results of γH2AX intensity produced by ICCM, which was obtained from different doses, demonstrated bystander signal accounted for the protective effects induced by intermediate dose of 100 mGy. The comparison of temporal kinetics and spatial dynamics of DNA repair between tritium β-rays and γ-rays showed longer time was need for the dephosphorylation of H2AX protein after HTO exposure. It indicated complex cluster DSBs induced by tritium β-rays at the low dose impaired efficient recovery of DNA damage, which bear responsibility for the persistence of residual foci after low dose expsoure. It suggests after exposed to low dose radiation cells prefer to eliminate damage population to avoid DNA damage increasing the mutation potential.

EFFECTIVE RADIATION DOSE OF 18F-FDG PET/CT: HOW MUCH DOES DIAGNOSTIC CT CONTRIBUTE?

The aim was to estimate the effective doses associated with different types of scanning protocols and how much the diagnostic computed tomography (DCT) scan contributed to the total dose of the dual-modality positron emission tomography/computed tomography (PET/CT) examinations. The results showed that an average radiation dose of 8.19 ± 0.83 mSv and 13.44 ± 5.14 mSv for the PET and CT components, respectively, resulting in a total dose of 21.64 ± 5.20 mSv. Approximately 92.7% (980 of 1057) of the patients underwent additional DCT protocols. The DCT protocols contributed 42% of the overall effective radiation doses, which was larger than the percentage contributed by the PET component (38%) and LCT protocols (20%). Reducing the diagnostic area of the DCT scans that patients undergo and decreasing the use of chest-abdomen-pelvis (CAP), abdomen-pelvis (AP) and chest DCT protocols, especially the CAP protocol, will be helpful in decreasing the effective radiation doses of PET/CT scan.

Internal doses from radionuclides and their health effects following the Fukushima accident

This paper presents an overview of current internal dose estimates from the Fukushima accident, potential population specific uncertainties in these estimates are investigated, along with the relative effects of internal and external exposures. Thyroid doses were largely due to ¹³¹I, but variations in thyroid weight and fractional uptake and retention times of ¹³¹I in the thyroid contribute to uncertainties in thyroid dose estimates. Lower values for these parameters in the Japanese population, as compared to international reference assumptions, would lead to underestimation of doses on the basis of reference thyroid weights and overestimation of doses using reference thyroid uptake and retention times. Any overall bias in thyroidal doses due to population specific factors is the net result of the balance between these effects. Internal doses to other organs are largely due to ¹³⁴Cs and ¹³⁷Cs and their whole body distribution, population specific differences in these dose estimates are driven by average body mass, due to the inverse relationship between this and retention times. Potential differences in dose estimates and any inferred risks, due to local population specific factors, may be less than a factor of two for children and male adults, but the potential difference may be slightly underestimated for female adults. Recent micro-dosimetric studies have confirmed the existing perception that risk from internal exposures to ¹³⁷Cs, ¹³⁴Cs, and ¹³¹I should be nearly equivalent to that from external exposure to gamma rays at the same absorbed dose. Epidemiological studies provide comparisons between external and internal exposures to ¹³¹I in children and suggest that effects of internal exposure are similar to those of external exposure. Effective dose has been formulated to harmonise internal and external exposure risks for radiation protection purposes. On the basis of this review, the use of effective dose in this context does not seem to be unreasonable.

Dosimetry of 175Ytterbium-poly (amidoamine) Therapy for Humans' Organs

Purpose:

This investigation focuses on biodistribution of irradiated dendrimer encapsulated ytterbium-175 (¹⁷⁵Yb) and to estimate the absorbed dose from intravenous injection of PAMAM encapsulated ¹⁷⁵Yb to human organs.

Methods:

A dendrimer compound containing an average of 55 Yb⁺³ ions per dendrimer was prepared and irradiated with neutrons for 2h at 3×10¹¹ n.cm-²s-¹ neutron flux. The resulting mixture was injected into a group of tumor bearing mice and the mice were excised, weighed and counted at certain times to study the biodistribution. The human organs absorbed dose was assessed by MIRD schema and MCNP simulation.

Results:

The specific activity and radiochemical purity of the irradiated nano-composite were 7MBq/mg and >99% respectively. The rapid up take of dendrimer was in liver, lung, and, spleen. MIRD and MCNPX were applied for dose estimation. The human absorbed dose in liver, lung, spleen, kidney and bone that simulated by MCNP are 1.266, 0.8081, 0.8347, 0.03979 and 0.01706 mGy/MBq respectively and these values for MIRD schema are 1.351, 0.73, 1.03, 0.039, and 0.0097 mGy/MBq respectively.

Conclusion:

The results showed that ¹⁷⁵Yb-PAMAM nano-radiopharmaceutical has potential of application for liver and lung tumors.

Surface radiation dose comparison of a dedicated extremity cone beam computed tomography (CBCT) device and a multidetector computed tomography (MDCT) machine in pediatric ankle and wrist phantoms

Objectives

To evaluate and compare surface doses of a cone beam computed tomography (CBCT) and a multidetector computed tomography (MDCT) device in pediatric ankle and wrist phantoms.

Methods

Thermoluminescent dosimeters (TLD) were used to measure and compare surface doses between CBCT and MDCT in a left ankle and a right wrist pediatric phantom. In both modalities adapted pediatric dose protocols were utilized to achieve realistic imaging conditions. All measurements were repeated three times to prove test-retest reliability. Additionally, objective and subjective image quality parameters were assessed.

Results

Average surface doses were 3.8 ±2.1 mGy for the ankle, and 2.2 ±1.3 mGy for the wrist in CBCT. The corresponding surface doses in optimized MDCT were 4.5 ±1.3 mGy for the ankle, and 3.4 ±0.7 mGy for the wrist. Overall, mean surface dose was significantly lower in CBCT (3.0 ±1.9 mGy vs. 3.9 ±1.2 mGy, p<0.001). Subjectively rated general image quality was not significantly different between the study protocols (p = 0.421), whereas objectively measured image quality parameters were in favor of CBCT (p<0.001).

Conclusions

Adapted extremity CBCT imaging protocols have the potential to fall below optimized pediatric ankle and wrist MDCT doses at comparable image qualities. These possible dose savings warrant further development and research in pediatric extremity CBCT applications.

Radioactively contaminated areas: Bioindicator species and biomarkers of effect in an early warning scheme for a preliminary risk assessment

Concerns about the impacts on public health and on the natural environment have been raised regarding the full range of operational activities related to uranium mining and the rest of the nuclear fuel cycle (including nuclear accidents), nuclear tests and depleted uranium from military ammunitions. However, the environmental impacts of such activities, as well as their ecotoxicological/toxicological profile, are still poorly studied. Herein, it is discussed if organisms can be used as bioindicators of human health effects, posed by lifetime exposure to radioactively contaminated areas. To do so, information was gathered from several studies performed on vertebrates, invertebrate species and humans, living in these contaminated areas. The retrieved information was compared, to determine which are the most used bioindicators and biomarkers and also the similarities between human and non-human biota responses. The data evaluated are used to support the proposal for an early warning scheme, based on bioindicator species and on the most sensitive and commonly shared biomarkers, to perform a screening evaluation of radioactively contaminated sites. This scheme could be used to support decision-making for a deeper evaluation of risks to human health, making it possible to screen a large number of areas, without disturbing and alarming local populations.

European Code against Cancer 4th Edition: Ionising and non-ionising radiation and cancer

Ionising radiation can transfer sufficient energy to ionise molecules, and this can lead to chemical changes, including DNA damage in cells. Key evidence for the carcinogenicity of ionising radiation comes from: follow-up studies of the survivors of the atomic bombings in Japan; other epidemiological studies of groups that have been exposed to radiation from medical, occupational or environmental sources; experimental animal studies; and studies of cellular responses to radiation. Considering exposure to environmental ionising radiation, inhalation of naturally occurring radon is the major source of radiation in the population - in doses orders of magnitude higher than those from nuclear power production or nuclear fallout. Indoor exposure to radon and its decay products is an important cause of lung cancer; radon may cause approximately one in ten lung cancers in Europe. Exposures to radon in buildings can be reduced via a three-step process of identifying those with potentially elevated radon levels, measuring radon levels, and reducing exposure by installation of remediation systems. In the 4th Edition of the European Code against Cancer it is therefore recommended to: "Find out if you are exposed to radiation from naturally high radon levels in your home. Take action to reduce high radon levels". Non-ionising types of radiation (those with insufficient energy to ionise molecules) - including extremely low-frequency electric and magnetic fields as well as radiofrequency electromagnetic fields - are not an established cause of cancer and are therefore not addressed in the recommendations to reduce cancer risk.

γ-H2AX Kinetic Profile in Mouse Lymphocytes Exposed to the Internal Emitters Cesium-137 and Strontium-90

In the event of a dirty bomb scenario or an industrial nuclear accident, a significant dose of volatile radionuclides such as 137Cs and 90Sr may be dispersed into the atmosphere as a component of fallout and inhaled or ingested by hundreds and thousands of people. To study the effects of prolonged exposure to ingested radionuclides, we have performed long-term (30 day) internal-emitter mouse irradiations using soluble-injected 137CsCl and 90SrCl2 radioisotopes. The effect of ionizing radiation on the induction and repair of DNA double strand breaks (DSBs) in peripheral mouse lymphocytes in vivo was determined using the γ-H2AX biodosimetry marker. Using a serial sacrifice experimental design, whole-body radiation absorbed doses for 137Cs (0 to 10 Gy) and 90Sr (0 to 49 Gy) were delivered over 30 days following exposure to each radionuclide. The committed absorbed doses of the two internal emitters as a function of time post exposure were calculated based on their retention parameters and their derived dose coefficients for each specific sacrifice time. In order to measure the kinetic profile for γ-H2AX, peripheral blood samples were drawn at 5 specific timed dose points over the 30-day study period and the total γ-H2AX nuclear fluorescence per lymphocyte was determined using image analysis software. A key finding was that a significant γ-H2AX signal was observed in vivo several weeks after a single radionuclide exposure. A mechanistically-motivated model was used to analyze the temporal kinetics of γ-H2AX fluorescence. Exposure to either radionuclide showed two peaks of γ-H2AX: one within the first week, which may represent the death of mature, differentiated lymphocytes, and the second at approximately three weeks, which may represent the production of new lymphocytes from damaged progenitor cells. The complexity of the observed responses to internal irradiation is likely caused by the interplay between continual production and repair of DNA damage, cell cycle effects and apoptosis.

Use of effective dose in medicine

This paper does not necessarily reflect the views of the International Commission on Radiological Protection. The protection quantity 'effective dose' was developed by the International Commission on Radiological Protection (ICRP) for use in the radiological protection of workers and the public. In this context, it is used as a risk-adjusted dosimetric quantity to optimise protection, comparing received or planned doses with constraints, reference levels, and limits expressed in the same quantity. Considering exposures incurred during medical procedures, effective dose can be of practical value for comparing: doses from different diagnostic examinations and interventional procedures; the use of similar technologies and procedures in different hospitals and countries; and the use of different technologies for the same medical examination, provided that the representative patients or patient populations for which the effective doses are derived are similar with regard to age and sex. However, as stated in ICRP Publication 103, '… risk assessment for medical diagnosis and treatment… is best evaluated using appropriate risk values for the individual tissues at risk and for the age and sex distribution of the individuals undergoing the medical procedures'. This topic was explored in a session of the First ICRP Symposium with arguments for and against the use of a new quantity referred to as 'effective risk', and examination of variations in estimated risk for different diagnostic procedures according to the age and sex of the exposed individuals. This paper restates the primary purposes of effective dose, and summarises estimates of variation in individual risk from medical procedures. The authors support the judicious use of effective dose as an indicator of possible risk, but caution against the use of effective risk as compared with the calculation of scientific best estimates of risk with consideration of associated uncertainties.

Impact of the adaptive statistical iterative reconstruction technique on image quality in ultra-low-dose CT

AIM

To evaluate the relationship between different noise indices (NIs) and radiation dose and to compare the effect of different reconstruction algorithm applications for ultra-low-dose chest computed tomography (CT) on image quality improvement and the accuracy of volumetric measurement of ground-glass opacity (GGO) nodules using a phantom study.

MATERIALS AND METHODS

A 11 cm thick transverse phantom section with a chest wall, mediastinum, and 14 artificial GGO nodules with known volumes (919.93 ± 64.05 mm(3)) was constructed. The phantom was scanned on a Discovery CT 750HD scanner with five different NIs (NIs = 20, 30, 40, 50, and 60). All data were reconstructed with a 0.625 mm section thickness using the filtered back-projection (FBP), 50% adaptive statistical iterative reconstruction (ASiR), and Veo model-base iterative reconstruction algorithms. Image noise was measured in six regions of interest (ROIs). Nodule volumes were measured using a commercial volumetric software package. The image quality and the volume measurement errors were analysed.

RESULTS

Image noise increased dramatically from 30.7 HU at NI 20 to 122.4 HU at NI 60, with FBP reconstruction. Conversely, Veo reconstruction effectively controlled the noise increase, with an increase from 9.97 HU at NI 20 to only 15.1 HU at NI 60. Image noise at NI 60 with Veo was even lower (50.8%) than that at NI 20 with FBP. The contrast-to-noise ratio (CNR) of Veo at NI 40 was similar to that of FBP at NI 20. All artificial GGO nodules were successfully identified and measured with an average relative volume measurement error with Veo at NI 60 of 4.24%, comparable to a value of 10.41% with FBP at NI 20. At NI 60, the radiation dose was only one-tenth that at NI 20.

CONCLUSION

The Veo reconstruction algorithms very effectively reduced image noise compared with the conventional FBP reconstructions. Using ultra-low-dose CT scanning and Veo reconstruction, GGOs can be detected and quantified with an acceptable accuracy.

Metal bioaccumulation, genotoxicity and gene expression in the European wood mouse (Apodemus sylvaticus) inhabiting an abandoned uranium mining area

Genotoxic effects caused by the exposure to wastes containing metals and radionuclides were investigated in the European wood mice (Apodemus sylvaticus). The animals were captured in the surroundings of an abandoned uranium mining site. DNA damage was assessed by comet assay; gene expression and single nucleotide polymorphisms (SNPs) were assessed, respectively, by Real-Time PCR and melt curve analysis. The bioaccumulation of metals in the liver, kidney and bones was also determined to help clarify cause-effect relationships. Results confirmed the bioaccumulation of cadmium and uranium in organisms exposed to uranium mining wastes. P53 gene was found to be significantly up-regulated in the liver of those organisms and SNPs in the Rb gene were also detected in the kidney. Our results showed that uranium mining wastes caused serious DNA damage resulting in genomic instability, disclosed by the significant increase in DNA strand breaks and P53 gene expression disturbance. These effects can have severe consequences, since they may contribute for the emergence of serious genetic diseases. The fact that mice are often used as bioindicator species for the evaluation of risks of environmental exposure to humans, raises concerns on the risks for human populations living near uranium mining areas.

Assessing the reliability of dose coefficients for inhaled and ingested radionuclides

Consideration of uncertainties on doses can provide numerical estimates of the reliability of the protection quantities (dose coefficients) used in radiation protection to assess exposures to radionuclides that enter the body by ingestion or inhalation ('internal emitters'). Uncertainty analysis methods have been widely applied to quantify uncertainties on doses, including effective dose. However, it is not always clear how the distributions of effective dose per unit intake that result from such analyses should be interpreted with respect to the intended use of effective dose in radiation protection and the use of dose coefficients as reference values. The ICRP system of radiological protection is reviewed briefly and it is argued that the reliability of an effective dose coefficient as a protection device can best be determined by comparing the nominal detriment adjusted cancer risk associated with the dose coefficient, with a best estimate of risk for the exposure pathway and exposed population group, considering uncertainties in biokinetic, dosimetric and risk parameters. Because it is the uncertainty on the population mean of this quantity that is required, the effect of parameter variability should be distinguished from the effect of parameter uncertainty when performing uncertainty analyses. A methodology for performing the uncertainty analysis is discussed and studies that quantify uncertainty on doses and risk from intakes of radionuclides are reviewed.

Uncertainty analysis of doses from ingestion of plutonium and americium

Uncertainty analyses have been performed on the biokinetic model for americium currently used by the International Commission on Radiological Protection (ICRP), and the model for plutonium recently derived by Leggett, considering acute intakes by ingestion by adult members of the public. The analyses calculated distributions of doses per unit intake. Those parameters having the greatest impact on prospective doses were identified by sensitivity analysis; the most important were the fraction absorbed from the alimentary tract, f(1), and rates of uptake from blood to bone surfaces. Probability distributions were selected based on the observed distribution of plutonium and americium in human subjects where possible; the distributions for f(1) reflected uncertainty on the average value of this parameter for non-specified plutonium and americium compounds ingested by adult members of the public. The calculated distributions of effective doses for ingested (239)Pu and (241)Am were well described by log-normal distributions, with doses varying by around a factor of 3 above and below the central values; the distributions contain the current ICRP Publication 67 dose coefficients for ingestion of (239)Pu and (241)Am by adult members of the public. Uncertainty on f(1) values had the greatest impact on doses, particularly effective dose. It is concluded that: (1) more precise data on f(1) values would have a greater effect in reducing uncertainties on doses from ingested (239)Pu and (241)Am, than reducing uncertainty on other model parameter values and (2) the results support the dose coefficients (Sv Bq(-1) intake) derived by ICRP for ingestion of (239)Pu and (241)Am by adult members of the public.

Evaluation of the sensitivity of genotoxicity and cytotoxicity endpoints in earthworms exposed in situ to uranium mining wastes

Earthworms were exposed for 56 days to a contaminated soil from an abandoned uranium mine and to the natural reference soil LUFA 2.2. The exposure occurred in situ: the containers with contaminated soil were placed near the mine pit; the containers with reference soil were placed in a reference site. For the assessment of metals bioaccumulation, DNA damages, cell-to-cell variation in DNA content, Median Fluorescence Intensity (MFI), coelomocytes frequency and proliferation, organisms were sampled after 0, 1, 2, 7, 14 and 56 days of exposure. For the assessment of radionuclides bioaccumulation, animals were sampled after 0, 14 and 56 days of exposure. As for growth, organisms were sampled after 0, 14, 28 and 56 days of exposure. The reproduction assay was performed according to the OECD (2004) guideline. DNA damages were assessed by comet assay and flow cytometry was used to determine cell-to-cell variation in DNA content, Median Fluorescence Intensity (MFI), coelomocytes frequency and proliferation. Results have shown a myriad of effects in the organisms exposed to the contaminated soil, namely: the inhibition of reproduction, growth reduction, DNA damages, cytotoxicity, changes in eleocytes fluorescence intensity, coelomocytes proliferation and bioaccumulation of metals and radionuclides. Our results showed that the evaluation of genotoxicity and cytotoxicity endpoints, along with other parameters at an individual level in standard reproduction assays conducted in situ, are important to improve the risk assessment process of areas contaminated with uranium and other radioactive mining wastes.

Risks from ionising radiation: an HPA viewpoint paper for Safegrounds

Safegrounds is a forum for developing and disseminating good practice guidance on the management of radioactively contaminated land on nuclear and defence sites in the UK. This review has been provided to Safegrounds as a summary of the basis for current radiation risk estimates and the International Commission on Radiological Protection (ICRP) protection system, in a form that will be accessible to a wide range of stakeholders. Safegrounds has also received viewpoint papers from other members who contend that the ICRP methodology results in substantial underestimates of risk, particularly for internal emitters. There is an extensive literature on the risks of radiation exposure, regularly reviewed by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and other expert groups. These data provide a sound basis for the system of protection recommended by ICRP. The available epidemiological and experimental evidence supports the application of cancer risk estimates derived for acute, high dose, external exposures to low dose exposures to external and internal sources. In the context of radioactively contaminated land on nuclear and defence sites, the national standards for the cleaning up of land and for waste disposal correspond to very low doses, two orders of magnitude less than average annual doses in the UK from natural background radiation (10-20  µSv compared with 2-3 mSv). Risks at such very low doses can only be estimated on the basis of observations after exposure of population groups at much higher doses. The estimated risks at these very low doses, while uncertain, are as likely to be overestimates as underestimates.

Doses to the red bone marrow of young people and adults from radiation of natural origin

Natural radiation sources comprise cosmic rays, terrestrial gamma rays, radionuclides in food and inhaled isotopes of radon with their decay products. These deliver doses to all organs and tissues including red bone marrow (RBM), the tissue in which leukaemia is thought to originate. In this paper we calculate the age-dependent annual RBM doses from natural radiation sources to young people and to adults at average levels of exposure in the UK. The contributions to dose are generally less complex than in the case of doses to foetuses and young children where it is necessary to take into account transfer of radionuclides across the placenta, intakes in mother's milk and changes in gut uptake in young infants. However, there is high uptake of alkaline earths and of similar elements in the developing skeleton and this significantly affects the doses from radioisotopes of these elements, not just in the teens and twenties but through into the fifth decade of life. The total equivalent dose to the RBM from all natural sources of radiation at age 15 years is calculated to be about 1200  µSv a year at average UK levels, falling to rather less than 1100  µSv per year in later life; the gentle fall from the late teens onwards reflects the diminishing effect of the high uptakes of radioisotopes of the alkaline earths and of lead in this period. About 60% of the equivalent dose is contributed by the low linear energy transfer (LET) component. Radionuclides in food make the largest contribution to equivalent doses to RBM and much the largest contribution to the absorbed dose from high LET radiation (mainly alpha particles).

Numbers and proportions of leukemias in young people and adults induced by radiation of natural origin

Natural sources contribute a large fraction of the radiation exposure of the general public. Under the linear no-threshold hypothesis risk decreases in proportion to decreasing dose without a threshold. We use recent estimates of doses to the red bone marrow to calculate the number and proportion of cases of leukemia in England induced by natural radiation. We calculate that about 5% of cases of leukemia, excluding chronic lymphocytic leukemia, up to the age of 80 years are induced by this background radiation. In young people up to the age of 25 years the attributable fraction is about 15%, substantially lower than a previous estimate.

Genotoxic endpoints in the earthworms sub-lethal assay to evaluate natural soils contaminated by metals and radionuclides

Eisenia andrei was exposed, for 56 days, to a contaminated soil from an abandoned uranium mine and to the natural reference soil LUFA 2.2. The organisms were sampled after 0, 1, 2, 7, 14 and 56 days of exposure, to assess metals bioaccumulation, coelomocytes DNA integrity and cytotoxicity. Radionuclides bioaccumulation and growth were also determined at 0 h, 14 and 56 days of exposure. Results have shown the bioaccumulation of metals and radionuclides, as well as, growth reduction, DNA damages and cytotoxicity in earthworms exposed to contaminated soil. The usefulness of the comet assay and flow cytometry, to evaluate the toxicity of contaminants such as metals and radionuclides in earthworms are herein reported. We also demonstrated that DNA strand breakage and immune cells frequency are important endpoints to be employed in the earthworm reproduction assay, for the evaluation of soil geno and cytotoxicity, as part of the risk assessment of contaminated areas. This is the first study that integrates DNA damage and cytotoxicity evaluation, growth and bioaccumulation of metals and radionuclides in a sub lethal assay, for earthworms exposed to soil contaminated with metals and radionuclides.

The divergence of science and simplicity in radiation protection

Several issues are discussed which are fundamental to the formulation of radiation protection standards: (1) the biological effectiveness of different radiations, (2) estimation of risks when different tissues or organs are irradiated, and (3) the models to be used when extrapolating estimated risks from high doses (and high dose rates) to low and very low doses and dose rates. The controversies regarding these issues are reviewed. Modifications to regulatory strategies and dose calculation methodology are suggested that may lessen the differences of opinion regarding these issues.

Dose conversion factors for radon: recent developments

Epidemiological studies of the occupational exposure of miners and domestic exposures of the public have provided strong and complementary evidence of the risks of lung cancer following inhalation of radon progeny. Recent miner epidemiological studies, which include low levels of exposure, long duration of follow-up, and good quality of individual exposure data, suggest higher risks of lung cancer per unit exposure than assumed previously by the International Commission on Radiological Protection (ICRP). Although risks can be managed by controlling exposures, dose estimates are required for the control of occupational exposures and are also useful for comparing sources of public exposure. Currently, ICRP calculates doses from radon and its progeny using dose conversion factors from exposure (WLM) to dose (mSv) based on miner epidemiological studies, referred to as the epidemiological approach. Revision of these dose conversion factors using risk estimates based on the most recent epidemiological data gives values that are in good agreement with the results of calculations using ICRP biokinetic and dosimetric models, the dosimetric approach. ICRP now proposes to treat radon progeny in the same way as other radionuclides and to publish dose coefficients calculated using models, for use within the ICRP system of protection.

The uneven irradiation of a target cell and its dynamic movement can mathematically explain incubation period for the induction of cancer by internally deposited radionuclides

Irradiation from internally deposited radionuclides induces malignant tumors. Ingested radionuclides accumulate in specific organs, which are irradiated over a lifelong period. Our aim is to elucidate why the development of malignant tumors requires long-term internal exposure, on the order of decades, despite the fact that irradiation is continuous over this period. Three major factors are considered to be responsible for the long incubation time in carcinogenesis caused by internally deposited alpha-emitters: uneven distribution of radionuclides, limited range of irradiation, and dynamic movement of tumor precursor cells. We hypothesized that target cells susceptible to malignant transformation may undergo one event by alpha particles and may then migrate outside of the range of alpha particles, thereby avoiding immediate induction of successive additional events that would lead to cell death or neoplastic changes. Based on this hypothesis, we further proposed a mathematical model to predict the relationship between dose rate and incubation period of tumors induced by internally deposited alpha-emitters. The function was non-linear and included terms of both direct and indirect radiation effects. It well fitted both human Th-ICC cases and rat Pu-induced lung cancer, suggesting that indirect radiation effects are independent from dose rate. The significance of parameters of the model is discussed.

Retention of tritium in reference persons: a metabolic model. Derivation of parameters and application of the model to the general public and to workers

Tritium ((3)H) is a radioactive isotope of hydrogen that is ubiquitous in environmental and biological systems. Following debate on the human health risk from exposure to tritium, there have been claims that the current biokinetic model recommended by the International Commission on Radiological Protection (ICRP) may underestimate tritium doses. A new generic model for tritium in mammals, based on energy metabolism and body composition, together with all its input data, has been described in a recent paper and successfully tested for farm and laboratory mammals. That model considers only dietary intake of tritium and was extended to humans. This paper presents the latest development of the human model with explicit consideration of brain energy metabolism. Model testing with human experimental data on organically bound tritium (OBT) in urine after tritiated water (HTO) or OBT intakes is presented. Predicted absorbed doses show a moderate increase for OBT intakes compared with doses recommended by the ICRP. Infants have higher tritium retention-a factor of 2 longer than the ICRP estimate. The highest tritium concentration is in adipose tissue, which has a very low radiobiological sensitivity. The ranges of uncertainty in retention and doses are investigated. The advantage of the new model is its ability to be applied to the interpretation of bioassay data.

Occupational and diagnostic exposure to ionizing radiation and leukemia risk among German uranium miners

Lung cancer is a well-known effect of radon exposure in uranium mines. However, little is known about the induction of leukemia by radiation exposure in mines. Moreover, miners usually have occupational medical checkup programs that include chest x-ray examinations. Therefore, the aim of the present study was to re-examine leukemia risk among miners, taking into account exposure to x rays for diagnostic purposes. The data used were from a previously analyzed individually matched case-control study of former uranium miners in East Germany with 377 cases and 980 controls. Additionally, data on x-ray examinations were taken from medical records for most of the subjects. Finally, the absorbed dose to red bone marrow was calculated considering both occupational and diagnostic exposures. Using conditional logistic regression models, a moderately but not statistically significant elevated risk was seen in the dose category above 200 mGy for the combined dose from both sources [odds ratio (OR) = 1.33, 90% confidence interval (CI): (0.82-2.14)]. Ignoring the dose accumulated in the recent 20 y, the risk in the highest dose category (>105 mGy) was higher [OR = 1.77, 90% CI: (1.06-2.95)]. Ignoring diagnostic exposure yielded similar results. For the highest dose category (absorbed dose lagged by 20 y) the risk was more than doubled [OR = 2.64, 90% CI: (1.60-4.35)].

Plutonium worker dosimetry

Epidemiological studies of the relationship between risk and internal exposure to plutonium are clearly reliant on the dose estimates used. The International Commission on Radiological Protection (ICRP) is currently reviewing the latest scientific information available on biokinetic models and dosimetry, and it is likely that a number of changes to the existing models will be recommended. The effect of certain changes, particularly to the ICRP model of the respiratory tract, has been investigated for inhaled forms of (239)Pu and uncertainties have also been assessed. Notable effects of possible changes to respiratory tract model assumptions are (1) a reduction in the absorbed dose to target cells in the airways, if changes under consideration are made to the slow clearing fraction and (2) a doubling of absorbed dose to the alveolar region for insoluble forms, if evidence of longer retention times is taken into account. An important factor influencing doses for moderately soluble forms of (239)Pu is the extent of binding of dissolved plutonium to lung tissues and assumptions regarding the extent of binding in the airways. Uncertainty analyses have been performed with prior distributions chosen for application in epidemiological studies. The resulting distributions for dose per unit intake were lognormal with geometric standard deviations of 2.3 and 2.6 for nitrates and oxides, respectively. The wide ranges were due largely to consideration of results for a range of experimental data for the solubility of different forms of nitrate and oxides. The medians of these distributions were a factor of three times higher than calculated using current default ICRP parameter values. For nitrates, this was due to the assumption of a bound fraction, and for oxides due mainly to the assumption of slower alveolar clearance. This study highlights areas where more research is needed to reduce biokinetic uncertainties, including more accurate determination of particle transport rates and long-term dissolution for plutonium compounds, a re-evaluation of long-term binding of dissolved plutonium, and further consideration of modeling for plutonium absorbed to blood from the lungs.

Relative toxicity of (45)Ca beta-particles and (242)Cm alpha-particles following their intravenous injection into mice as radiolabelled FAP

PURPOSE

To determine the relative toxicity of alpha- and beta-radiations under conditions of controlled temporal and spatial dose distribution.

METHODS

Fused aluminosilicate particles were radiolabelled with either (45)Ca (a beta-emitter) or (242)Cm (an alpha-emitter). These were injected into CBA/Ca mice to give lifespan, whole-body doses of approximately 0.5, 1.0 or 1.5 Gy. Most animals were entered into a lifespan toxicity study, but some were killed for radiochemical analysis and autoradiography.

RESULTS

Twenty-seven tumour types were identified. The most common malignant tumours were: Mammary carcinoma; liver carcinoma; malignant lymphoma; uterine histiocytic sarcoma. Excess relative risk (strictly hazard ratio) was higher for radiation-induced carcinomas than for sarcomas. The carcinomas, but not sarcomas showed a reduction in relative risk at the highest radiation dose employed. This reduction was most easily attributed to a systemic effect. The highest relative toxicity measured was for liver carcinoma (5.9, 95% confidence intervals [CI] 2.4, 14) and the lowest for uterine carcinoma (0.6, CI 0.03, 9.7). Overall, the excess relative risk ratio for SURVIVAL WAS 1.9 (CI 1.1, 3.2), FOR ALL CARCINOMA WAS 2.3 (CI 1.7, 3.0) AND FOR ALL SARCOMA WAS 2.7 (CI 0.72, 10).

CONCLUSIONS

The 10-fold variability in the observed toxicity ratio for different tumour endpoints shows that tissue sensitivity is a more important determinant of relative toxicity than radiation quality. The use of single radiation-weighting (w(R)) factors for radiation risk prediction and for radiological protection dosimetry is inconsistent with scientific observation.

Updated estimates of the proportion of childhood leukaemia incidence in Great Britain that may be caused by natural background ionising radiation

The aetiology of childhood leukaemia remains generally unknown, although exposure to moderate and high levels of ionising radiation, such as was experienced during the atomic bombings of Japan or from radiotherapy, is an established cause. Risk models based primarily upon studies of the Japanese A-bomb survivors imply that low-level exposure to ionising radiation, including to ubiquitous natural background radiation, also raises the risk of childhood leukaemia. In a recent paper (Wakeford et al 2009 Leukaemia 23 770-6) we estimated the proportion of childhood leukaemia incidence in Great Britain attributable to natural background radiation to be about 20%. In this paper we employ the two sets of published leukaemia risk models used previously, but use recently published revised estimates of natural background radiation doses received by the red bone marrow of British children to update the previous results. Using the newer dosimetry we calculate that the best estimate of the proportion of cases of childhood leukaemia in Great Britain predicted to be attributable to this source of exposure is 15-20%, although the uncertainty associated with certain stages in the calculation (e.g. the nature of the transfer of risk between populations and the pertinent dose received from naturally occurring alpha-particle-emitting radionuclides) is significant. The slightly lower attributable proportions compared with those previously derived by Wakeford et al (Leukaemia 2009 23 770-6) are largely due to the lower doses (and in particular lower high LET doses) for the first year of life.

Understanding and characterisation of the risks to human health from exposure to low levels of radiation

Exposure to ionising radiation can lead to a wide variety of health effects. Cancer is judged to be the main risk from radiation at low doses and low dose rates, and controlling this risk has been the main factor in developing radiation protection practice. Conventional paradigms of radiobiology and radiation carcinogenesis have served to guide extrapolations of epidemiological data on exposed human populations, so as to estimate risks at low doses and low dose rates, to other types of ionising radiation and to non-uniform exposures. These paradigms are founded on a century of experimental and theoretical studies, but nevertheless there remain many uncertainties. Major assumptions and simplifications have been introduced to achieve a practical system of additive doses (and implied risks) for radiation protection. Advancing epidemiological studies and experimental research continue to reduce uncertainties in some areas while, in others, they raise new challenges to the generality and applicability of the conventional paradigms.

Doses and risks from tritiated water and environmental organically bound tritium

This short review provides an explanation of the calculation and use of the ICRP protection quantities, equivalent and effective dose, including the simplifications introduced by using radiation and tissue weighting factors. It discusses the dose coefficients (Sv Bq(-1) intake) provided by ICRP for intakes of tritiated water (HTO) and organically bound tritium (OBT) and considers uncertainties in the human and animal data on which they are based, including information on the relative biological effectiveness (RBE) of tritium beta particles compared to gamma and x-rays. The review also addresses the specific issue of dose coefficients for ingestion of OBT in Cardiff Bay fish. A distinction is drawn between the adequacy of the ICRP calculation of effective dose to a reference person for the purposes of planning and regulatory control, and the calculation of best estimates of dose and risk to individuals. ICRP will continue to use a radiation weighting factor of 1 for all low LET radiations in the calculation of effective dose, but specific RBE data should be used in risk estimates. Uncertainties in dose coefficients are small for HTO but greater for OBT. The generic consideration of OBT provided by ICRP may not be appropriate for specific organic forms such as OBT in fish.

The relevance of dose for low-energy beta emitters

Specific issues in risk assessment for low-energy beta emitters include specification of the radiation weighting factor, values of relative biological effectiveness for specific or accurate risk estimates, non-uniformities of dose within tissues and cells, and use of standard tissue weighting factors for non-uniform situations. Unusual features of low-energy beta emitters include: increased average ionisation density on subcellular (and cellular) scales; short ranges of the beta electrons; non-uniformity of the absorbed dose over subcellular, cellular, and tissue dimensions; reduced hit frequencies; nuclear transmutations; different chemical forms, influencing biokinetics and dose distributions; and large isotopic mass differences, particularly in the case of tritium and hydrogen. Many of these features are not included explicitly in conventional radiation protection dosimetry, although they may be partly included in experimental determinations of relative biological effectiveness. Theoretical and experimental studies have shown low-energy electrons to be particularly efficient in producing double-strand breaks in DNA, including complex double-strand breaks. Hence, on fundamental grounds, tritium beta particles should be expected to have greater biological effectiveness per unit absorbed dose than (60)Co gamma-rays or orthovoltage x-rays. For practical purposes, and in view of the paucity of epidemiological estimates of risk from low-energy electrons, consideration should be given to applying a raised relative biological effectiveness, say of value 2, to all low-energy internal emitters, including beta particles and soft x-ray emissions.

Biokinetic and dosimetric modelling in the estimation of radiation risks from internal emitters

The International Commission on Radiological Protection (ICRP) has developed biokinetic and dosimetric models that enable the calculation of organ and tissue doses for a wide range of radionuclides. These are used to calculate equivalent and effective dose coefficients (dose in Sv Bq(-1) intake), considering occupational and environmental exposures. Dose coefficients have also been given for a range of radiopharmaceuticals used in diagnostic medicine. Using equivalent and effective dose, exposures from external sources and from different radionuclides can be summed for comparison with dose limits, constraints and reference levels that relate to risks from whole-body radiation exposure. Risk estimates are derived largely from follow-up studies of the survivors of the atomic bombings at Hiroshima and Nagasaki in 1945. New dose coefficients will be required following the publication in 2007 of new ICRP recommendations. ICRP biokinetic and dosimetric models are subject to continuing review and improvement, although it is arguable that the degree of sophistication of some of the most recent models is greater than required for the calculation of effective dose to a reference person for the purposes of regulatory control. However, the models are also used in the calculation of best estimates of doses and risks to individuals, in epidemiological studies and to determine probability of cancer causation. Models are then adjusted to best fit the characteristics of the individuals and population under consideration. For example, doses resulting from massive discharges of strontium-90 and other radionuclides to the Techa River from the Russian Mayak plutonium plant in the early years of its operation are being estimated using models adapted to take account of measurements on local residents and other population-specific data. Best estimates of doses to haemopoietic bone marrow, in utero and postnatally, are being used in epidemiological studies of radiation-induced leukaemia. Radon-222 is the one internal emitter for which control of exposure is based on direct information on cancer risks, with extensive information available on lung cancer induction by radon progeny in mines and consistent data on risks in homes. The dose per unit (222)Rn exposure can be calculated by comparing lung cancer risk estimates derived for (222)Rn exposure and for external exposure of the Japanese survivors. Remarkably similar values are obtained by this method and by calculations using the ICRP model of the respiratory tract, providing good support for model assumptions. Other informative comparisons with risks from external exposure can be made for Thorotrast-induced liver cancer and leukaemia, and radium-induced bone cancer. The bone-seeking alpha emitters, plutonium-239 and radium isotopes, are poorer leukaemogens than predicted by models. ICRP dose coefficients are published as single values without consideration of uncertainties. However, it is clear that full consideration of uncertainties is appropriate when considering best estimates of doses and risks to individuals or specific population groups. An understanding of the component uncertainties in the calculation of dose coefficients can be seen as an important goal and should help inform judgements on the control of exposures. The routine consideration of uncertainties in dose assessments, if achievable, would be of questionable value when doses are generally maintained at small fractions of limits.

Dose to red bone marrow of infants, children and adults from radiation of natural origin

Natural radiation sources contribute much the largest part of the radiation exposure of the average person. This paper examines doses from natural radiation to the red bone marrow, the tissue in which leukaemia is considered to originate, with particular emphasis on doses to children. The most significant contributions are from x-rays and gamma rays, radionuclides in food and inhalation of isotopes of radon and their decay products. External radiation sources and radionuclides other than radon dominate marrow doses at all ages. The variation with age of the various components of marrow dose is considered, including doses received in utero and in each year up to the age of 15. Doses in utero include contributions resulting from the ingestion of radionuclides by the mother and placental transfer to the foetus. Postnatal doses include those from radionuclides in breast-milk and from radionuclides ingested in other foods. Doses are somewhat higher in the first year of life and there is a general slow decline from the second year of life onwards. The low linear energy transfer (LET) component of absorbed dose to the red bone marrow is much larger than the high LET component. However, because of the higher radiation weighting factor for the latter it contributes about 40% of the equivalent dose incurred up to the age of 15.

The radiobiology/radiation protection interface in healthcare

The current knowledge of radiation effects is reviewed and implications for its application in healthcare considered. The 21st L H Gray conference gathered leading experts in radiobiology, radiation epidemiology, radiation effect modelling, and the application of radiation in medicine to provide an overview of the subject. The latest radiobiology research in non-targeted effects such as genomic instability and the bystander effect challenge the old models, but the implications for health effects on humans are uncertain. Adaptive responses to external stresses, of which radiation is one, have been demonstrated in cells and animal models, but it is not known how these might modify human dose-effect relationships. Epidemiological evidence from the Japanese A-bomb survivors provides strong evidence that there is a linear relationship between the excess risk of cancer and organ dose that extends from about 50 mSv up to 2.5 Sv, and results from pooled data for multiple epidemiological studies indicate that risks extend down to doses of 20 mSv. Thus linear extrapolation of the A-bomb dose-effect data provides an appropriate basis for radiological protection standards at the present time. Risks from higher dose diagnostic procedures fall within the range in which health effects can be demonstrated. There is therefore reason for concern about the rise in the number of computed tomography (CT) scans performed in many countries, and in particular the use of CT for screening of asymptomatic individuals. New radiotherapy techniques allow high dose radiation fields to be conformed more effectively to target volumes, and reduce doses to critical organs, but they tend to give a higher and more uniform dose to the whole body which may increase the risk of second cancer. It is important that radiation protection practitioners keep abreast of developments in understanding of radiation effects and advise the medical community about the implications of fundamental research when planning medical applications for the future.

ICRP Publication 105. Radiation protection in medicine

This report was prepared to underpin the Commission's 2007 Recommendations with regard to the medical exposure of patients, including their comforters and carers, and volunteers in biomedical research. It addresses the proper application of the fundamental principles (justification, optimisation of protection, and application of dose limits) of the Commission's 2007 Recommendations to these individuals. With regard to medical exposure of patients, it is not appropriate to apply dose limits or dose constraints, because such limits would often do more harm than good. Often, there are concurrent chronic, severe, or even life-threatening medical conditions that are more critical than the radiation exposure. The emphasis is then on justification of the medical procedures and on the optimisation of radiological protection. In diagnostic and interventional procedures, justification of procedures (for a defined purpose and for an individual patient), and management of the patient dose commensurate with the medical task, are the appropriate mechanisms to avoid unnecessary or unproductive radiation exposure. Equipment features that facilitate patient dose management, and diagnostic reference levels derived at the appropriate national, regional, or local level, are likely to be the most effective approaches. In radiation therapy, the avoidance of accidents is a predominant issue. With regard to comforters and carers, and volunteers in biomedical research, dose constraints are appropriate. Over the last decade, the Commission has published a number of documents that provided detailed advice related to radiological protection and safety in the medical applications of ionising radiation. Each of the publications addressed a specific topic defined by the type of radiation source and the medical discipline in which the source is applied, and was written with the intent of communicating directly with the relevant medical practitioners and supporting medical staff. This report consolidates that advice.