Activity estimation and biokinetic analysis of 99mTc-DMSA in renal infant patients using a gamma camera

Biokinetic data from the administration of radiopharmaceuticals is essential in nuclear medicine dosimetry. It has particular significance in children, as their metabolism is very different from adults. Biokinetic models for paediatric patients could therefore need to be adapted to better reflect their absorption, retention and excretion functions, when compared to adults. Obtaining quality in vivo infant or paediatric biokinetic data is then essential to improve the available reference models, which in turn can lead to the optimization of paediatric procedures and protocols in clinical practice.This study analyses the biokinetic behaviour of ^99mTc-dimercaptosuccinic acid (DMSA), in 8 infants aged 4 months to 2 years old, through an imaging study using a gamma camera, and compares the obtained values with those obtained with the reference ICRP biokinetic model. The in vivo data was treated using an adapted methodology from the MIRD 16 pamphlet. Activity curves for the liver, the kidney and the whole body, were built, and new effective absorption, retention and excretion half-lives were estimated, and compared with the reference biokinetic parameters of ICRP 128. The obtained residence time in the kidneys of 2.56 h, has a deviation of 30.8% to the ICRP 128 value of 3.70 h. The obtained maximum uptake in the kidneys was of 0.22/A₀, which compares to the value of 0.31/A₀ for ICRP.The obtained biokinetic parameters were used to estimate the absorbed dose. The obtained dose values are smaller than the reference ICRP 128 ones by 32.1% in the kidneys, and 18.4% in the liver.     

The conversion of exposures due to radon into the effective dose: the epidemiological approach

The risks and dose conversion coefficients for residential and occupational exposures due to radon were determined with applying the epidemiological risk models to ICRP representative populations. The dose conversion coefficient for residential radon was estimated with a value of 1.6 mSv year^?1 per 100 Bq m^?3 (3.6 mSv per WLM), which is significantly lower than the corresponding value derived from the biokinetic and dosimetric models. The dose conversion coefficient for occupational exposures with applying the risk models for miners was estimated with a value of 14 mSv per WLM, which is in good accordance with the results of the dosimetric models. To resolve the discrepancy regarding residential radon, the ICRP approaches for the determination of risks and doses were reviewed. It could be shown that ICRP overestimates the risk for lung cancer caused by residential radon. This can be attributed to a wrong population weighting of the radon-induced risks in its epidemiological approach. With the approach in this work, the average risks for lung cancer were determined, taking into account the age-specific risk contributions of all individuals in the population. As a result, a lower risk coefficient for residential radon was obtained. The results from the ICRP biokinetic and dosimetric models for both, the occupationally exposed working age population and the whole population exposed to residential radon, can be brought in better accordance with the corresponding results of the epidemiological approach, if the respective relative radiation detriments and a radiation-weighting factor for alpha particles of about ten are used.     

Influence of human biokinetics of strontium on internal ingestion dose of <Superscript>90</Superscript>Sr and absorbed dose of <Superscript>89</Superscript>Sr to organs and metastases

The objective of the present work is to apply the plasma clearance parameters to strontium, previously determined in our laboratory, to improve the biokinetic and dosimetric models of strontium-90 (⁹⁰Sr) used in radiological protection; and also to apply this data for the estimation of the radiation doses from strontium-89 (⁸⁹Sr) after administration to patients for the treatment of the painful bone metastases. Plasma clearance and urinary excretion of stable strontium tracers of strontium-84 (⁸⁴Sr) and strontium-86 (⁸⁶Sr) were measured in GSF-National Research Center for Environment and Health (GSF) in 13 healthy German adult subjects after intravenous injection and oral administration. The biological half-life of strontium in plasma was evaluated from 49 plasma concentration data sets following intravenous injections. This value was used to determine the transfer rates from plasma to other organs and tissues. At the same time, the long-term retention of strontium in soft tissue and whole body was constrained to be consistent with measured values available. A physiological urinary path was integrated into the biokinetic model of strontium. Parameters were estimated using our own measured urinary excretion values. Retention and excretion of strontium were modeled using compartmental transfer rates published by the International Commission on Radiological Protection (ICRP), the SENES Oak Ridge Inc. (SENES), and the Urals Research Center for Radiation Medicine (TBM). The results were compared with values calculated by applying our GSF parameters (GSF). For the dose estimation of ⁸⁹Sr, a bone metastases model (GSF-M) was developed by adding a compartment, representing the metastases, into the strontium biokinetic model. The related parameters were evaluated based on measured data available in the literature. A set of biokinetic parameters was optimized to represent not only the early plasma kinetics of strontium but also the long-term retention measured in soft tissue and whole body. The ingestion dose coefficients of ⁹⁰Sr were computed and compared with different biokinetic model parameters. The ingestion dose coefficients were calculated as 2.8 × 10⁻⁸, 2.1 × 10⁻⁸, 2.5 × 10⁻⁸ and 3.8 × 10⁻⁸ Sv Bq⁻¹ for ICRP, SENES, TBM and GSF model parameters, respectively. Moreover, organ absorbed dose for the radiopharmaceutical of ⁸⁹Sr in bone metastases therapy was estimated based on the GSF and ICRP biokinetic model parameters. The effective doses were 3.3, 1.8 and 1.2 mSv MBq⁻¹ by GSF, GSF-M, and ICRP Publication 67 model parameters, respectively, compared to the value of 3.1 mSv MBq⁻¹ reported by ICRP Publication 80. The absorbed doses of red bone marrow and bone surface, 17 and 21 mGy MBq⁻¹ calculated by GSF parameters, and 7.1 and 8.8 mGy MBq⁻¹ by GSF-M parameters, are comparable to the clinical results of 3–19 mGy MBq⁻¹ for bone marrow and 16 mGy MBq⁻¹ for bone surface. Based on the GSF-M model, the absorbed dose of ⁸⁹Sr to metastases was estimated to be 434 mGy MBq⁻¹. The strontium clearance half-life of 0.25 h from the plasma obtained in the present study is obviously faster than the value of 1.1 h recommended by ICRP. There are no significant changes for ingestion dose coefficients of ⁹⁰Sr using different model parameters. A model including the metastases was particularly developed for dose estimation of ⁸⁹Sr treatment for the pain of bone metastases.     

<Superscript>131</Superscript>I age-dependent inhalation dose in Southern Poland from Fukushima accident

A general method for calculating doses absorbed from isotopes released in nuclear accidents is presented. As an example, this method was used to calculate doses for inhabitants of Southern Poland due to inhalation of ¹³¹I released due to the Fukushima nuclear plant accident. ¹³¹I activity measurements in the air of that region provided the basis for the study. The proposed model is based on a complex biokinetic model for iodine merging the Leggett model developed in 2010 with the human respiratory tract and gastrointestinal tract models recommended by the International Commission on Radiological Protection (ICRP). This model is described here, and it is demonstrated that resulting dose estimates are consistent with those obtained using the ICRP methodology. Using the developed model, total doses were calculated for six age groups of both genders, for gaseous and aerosol fractions alike. The committed effective dose, H ₅₀, for an adult man reached 16 nSv, which is lower than 0.001% of the background dose. The dose for the thyroid of an adult reached 0.33 μSv, which corresponds to circa 0.0007% of the dose to the population of Southern Poland after the Chernobyl nuclear plant accident.     

Feasibility of reducing differences in estimated doses in nuclear medicine between a patient-specific and a reference phantom

The feasibility of reducing the differences between patient-specific internal doses and doses estimated using reference phantoms was evaluated. Relatively simple adjustments to a polygon-surface ICRP adult male reference phantom were applied to fit selected individual dimensions using the software Rhinoceros®4.0. We tested this approach on two patient-specific phantoms: the biggest and the smallest phantoms from the Helmholtz Zentrum München library. These phantoms have unrelated anatomy and large differences in body-mass-index. Three models approximating each patient’s anatomy were considered: the voxel and the polygon-surface ICRP adult male reference phantoms and the adjusted polygon-surface reference phantom. The Specific Absorbed Fractions (SAFs) for internal photon and electron sources were calculated with the Monte Carlo code EGSnrc. Employing the time-integrated activity coefficients of a radiopharmaceutical (S)-4-(3-¹⁸F-fluoropropyl)-l-glutamic acid and the calculated SAFs, organ absorbed-dose coefficients were computed following the formalism promulgated by the Committee on Medical Internal Radiation Dose. We compared the absorbed-dose coefficients between each patient-specific phantom and other models considered with emphasis on the cross-fire component. The corresponding differences for most organs were notably lower for the adjusted reference models compared to the case when reference models were employed. Overall, the proposed approach provided reliable dose estimates for both tested patient-specific models despite the pronounced differences in their anatomy. To capture the full range of inter-individual anatomic variability more patient-specific phantoms are required. The results of this test study suggest a feasibility of estimating patient-specific doses within a relative uncertainty of 25% or less using adjusted reference models, when only simple phantom scaling is applied.     

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 ²³⁹Pu 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 ²³⁹Pu 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.     

Biokinetic modeling of uranium in man after injection and ingestion

Uranium is a naturally occurring primordial radioactive element. Small amounts found in air, water, and food are regularly consumed and inhaled by humans. Even the military, medical, and industrial use of depleted uranium can affect humans. There is an appreciable retention of incorporated uranium in skeleton, kidneys, and liver, and a review of respective effective dose coefficients has been given by the International Commission on Radiological Protection (ICRP) in its "Publication 69"; however, data regarding retention in organs or tissues and rates of urinary and fecal excretion for different age groups are incomplete. Therefore, the present study provides retention data that have been calculated for uranium in all compartments and for urinary and fecal excretion, following acute and chronic injection and ingestion for six age groups. The calculations are based on the current ICRP biokinetic model for uranium, and the data can be plotted by using any mathematical software to obtain the retention data at any time after incorporation or to calculate the internal average organ dose induced by uranium provided that specific absorbed fractions are available. The dynamic relationship of the retention in plasma and blood after intravenously and orally administered uranium can easily be derived from the database for injection and ingestion. The calculated contents of uranium in organs or tissues (using the uranium concentration in foodstuffs published by UNSCEAR for Europeans) are compared with autopsy data available in the literature. According to this model, the whole body of a 75-year-old man contains 7 microg uranium, of which 76% is in the skeleton, 1% in the kidneys, and 2.1% in the liver.     

Comparison of dose conversion factors for radon progeny from the ICRP 66 regional model and an airway tube model of tracheo-bronchial tree

Current epidemiological approaches to radon dosimetry yield a dose conversion factor (DCF) of 4 mSv WLM⁻¹ while the dosimetric approaches give a value closer to 13 mSv WLM⁻¹. The present study investigated whether the application of compartment models for the bronchial (BB) and bronchiolar (bb) regions, rather than more anatomically realistic airway tube models, has brought the dosimetric DCF to the higher values. The airway tube model of the tracheo-bronchial tree was used to calculate the effective dose per unit radon exposure. All other elements of the human respiratory tract from the reports of the ICRP or NRC were adopted. A dosimetric derivation of the radon DCF using the airway tube model yielded a value of 14.2 mSv WLM⁻¹. This value is slightly larger than, but not significantly different from, the result obtained through the ICRP 66 approach. It is concluded that utilization of the airway tube model instead of the regional ICRP 66 compartmental model cannot reconcile the gap between dose conversion factors derived from epidemiological and dosimetric approaches.     

Calculation of tumour and normal tissue biological effective dose in 90Y liver radioembolization with different dosimetric methods

PurposeRadioembolization with ⁹⁰Y microspheres is an effective treatment for unresectable liver tumours. Two types of microspheres are available: resin (SIR-Spheres®) and glass (Theraspheres®). The aim of this study is to compare biological effective dose (BED) values obtained with three different dosimetric methods.Methods29 HCC patients were included in this study: 15 were treated with resin(mean injected activity 1.5 GBq, range 0.8–2.7 GBq) and 14 with glass microspheres (2.6 GBq, range 1.3–4.1 GBq). Average doses to tumours and normal liver tissues were calculated with AAPM, multi-compartmental MIRD and Voxel-based methods and consequently the BED values were obtained. Planar images were used for the AAPM method: ^99mTc-MAA SPECT-CT attenuation and scatter corrected images (resin) and ⁹⁹m Tc-MAA SPECT attenuation corrected (glass) were employed for the other two methods.ResultsRegardless of type of microspheres, both for tumours and normal liver tissues, no significant statistical differences were found between MIRD and Voxel for both doses and BED values. Conversely AAPM gave discordant results with respect to the other two methods (Mann-Whitney p-values ⩽ 0.01). For resin spheres the calculated tumour-to-normal tissue ratios on planar images were on average 14 times greater than those obtained on SPECT-CT images, while they were 4 times greater on glass. A linear correlation was observed between MIRD and Voxel BEDs.ConclusionsThe AAPM method appears to be less precise for absorbed dose and BED estimation, while MIRD and voxel based dosimetry are more confident each other.     

Le radiophysicien,l’enfant et la pédiatrie

Estimation of the absorbed dose in nuclear pediatric is mandatory and necessary to assess the risk in radiation protection of each child. The radiophysicist plays an essential role in this process because he has the knowledge for this evaluation. This work aims to compare different dosimetric methods in the literature. All are based on the most used in this domain, “MIRD method”. The maximum relative deviations are 30% for three tests studied and do not set a reference.     

Dosimetric characterization of an 192Ir brachytherapy source with the Monte Carlo code PENELOPE

Monte Carlo calculations are highly spread and settled practice to calculate brachytherapy sources dosimetric parameters. In this study, recommendations of the AAPM TG-43U1 report have been followed to characterize the Varisource VS2000 ¹⁹²Ir high dose rate source, provided by Varian Oncology Systems.In order to obtain dosimetric parameters for this source, Monte Carlo calculations with PENELOPE code have been carried out. TG-43 formalism parameters have been presented, i.e., air kerma strength, dose rate constant, radial dose function and anisotropy function. Besides, a 2D Cartesian coordinates dose rate in water table has been calculated. These quantities are compared to this source reference data, finding results in good agreement with them.The data in the present study complement published data in the next aspects: (i) TG-43U1 recommendations are followed regarding to phantom ambient conditions and to uncertainty analysis, including statistical (type A) and systematic (type B) contributions; (ii) PENELOPE code is benchmarked for this source; (iii) Monte Carlo calculation methodology differs from that usually published in the way to estimate absorbed dose, leaving out the track-length estimator; (iv) the results of the present work comply with the most recent AAPM and ESTRO physics committee recommendations about Monte Carlo techniques, in regards to dose rate uncertainty values and established differences between our results and reference data.The results stated in this paper provide a complete parameter collection, which can be used for dosimetric calculations as well as a means of comparison with other datasets from this source.     

Multicellular dosimetric chain for molecular radiotherapy exemplified with dose simulations on 3D cell spheroids

PurposeAbsorbed radiation dose-response relationships are not clear in molecular radiotherapy (MRT). Here, we propose a voxel-based dose calculation system for multicellular dosimetry in MRT. We applied confocal microscope images of a spherical cell aggregate i.e. a spheroid, to examine the computation of dose distribution within a tissue from the distribution of radiopharmaceuticals.MethodsA confocal microscope Z-stack of a human hepatocellular carcinoma HepG2 spheroid was segmented using a support-vector machine algorithm and a watershed function. Heterogeneity in activity uptake was simulated by selecting a varying amount of the cell nuclei to contain ¹¹¹In, ¹²⁵I, or ¹⁷⁷Lu. Absorbed dose simulations were carried out using vxlPen, a software application based on the Monte Carlo code PENELOPE.ResultsWe developed a schema for radiopharmaceutical dosimetry. The schema utilizes a partially supervised segmentation method for cell-level image data together with a novel main program for voxel-based radiation dose simulations. We observed that for ¹⁷⁷Lu, radiation cross-fire enabled full dose coverage even if the radiopharmaceutical had accumulated to only 60% of the spheroid cells. This effect was not found with ¹¹¹In and ¹²⁵I. Using these Auger/internal conversion electron emitters seemed to guarantee that only the cells with a high enough activity uptake will accumulate a lethal amount of dose, while neighboring cells are spared.ConclusionsWe computed absorbed radiation dose distributions in a 3D-cultured cell spheroid with a novel multicellular dosimetric chain. Combined with pharmacological studies in different tissue models, our cell-level dosimetric calculation method can clarify dose-response relationships for radiopharmaceuticals used in MRT.     

Biokinetic measurements and modelling of urinary excretion of cerium citrate in humans

Tracer kinetics in healthy human volunteers was studied applying stable isotopes of cerium citrate to obtain biokinetic human data for the urinary excretion of cerium. These data were then used to compare and validate the biokinetic model for lanthanides (cerium) proposed by Taylor and Leggett (Radiat Prot Dosim 105:193–198, 2003), which is substantially improved and more realistic than the biokinetic model currently recommended by the International Commission on Radiological Protection (ICRP Publication 67, 1993); both models are primarily based on animal data. In the present study, 16 adults were investigated and two cerium tracers were simultaneously administered, both intravenously and/or orally. The cerium concentrations in urine were determined by inductively coupled plasma mass spectrometry. Ingested cerium citrate was poorly absorbed, and its low excretion was similar to the prediction of the biokinetic model of Taylor and Leggett. In contrast, after injection of cerium citrate its urinary excretion was rapidly increased, and the model underestimated the experimental results. These results suggest that urinary excretion of cerium may be dependent on the administered chemical form of cerium (speciation).     

Quantitative plutonium microdistribution in bone tissue of vertebra from occupationally exposed worker

The purpose of this work is the receiving of quantitative data on Pu microdistribution in different structural elements of human bone tissue for local dose assessment and dosimetric models validation. Thoracic vertebra sample was taken for the study from former Mayak worker with rather high Pu burden, including information on occupational and exposure history, medical information and data on Pu content in organs. Lexan film autodiagrams were obtained using method of neutron-induced autoradiography from bone tissue sections. Quantitative analysis of randomly selected vision fields on one of autoradiograms was performed: fission fragment tracks Pu in different bone tissue areas were calculated, surface of bone tissue areas were defined. Quantitative information on Pu microdistribution in human bone tissue was obtained for the first time. On the basis of obtained data quantitative relation of Pu decays in bone volume to decays on bone surface in cortical and trabecular fractions were defined as 2.0 and 0.4, correspondingly. Actual quantitative relation of decays in bone volume to decays on bone surface is significantly different from recommended by ICRP for cortical fraction. Biokinetic model parameters of extrapulmonary ICRP compartment might need to be adjusted after expansion of data set on quantitative Pu microdistribution in other bone types in human that will involve new cases with different exposure pattern of radionuclide.     

Effects of cross-section structure on the dosimetric response functions for 0.4 to 10.0 MeV neutrons in the ICRU tissue sphere

The effect of the fluctuating cross-section structure in the energy range of 0.4 to 10.0 MeV on the dosimetric response functions of neutrons in the ICRU standard tissue sphere is analyzed. A Monte Carlo method with point-energy cross-section values, including coupled transport for neutrons and secondary charged particles, was used in the direct estimation of the absorbed dose and the dose equivalent. An approach was adopted in which source-energy band-average responses were calculated instead of the more usual approach involving monoenergetic source neutrons. Data were obtained for the newly defined term, ambient dose equivalent, at various depths, as well as the older index quantities. Such data generated were compared with information from other research workers. In general, good agreement was found, with due consideration to the differences engendered by the use of the source-energy band-average approach. Agreement was poorest for very shallow depths, corresponding to outer skin thickness, this being a most difficult depth to calculate accurately. The dosimetric data generated in this study should contribute to the ongoing efforts for the standardization of neutron protection dosimetry.     

A Monte Carlo model for the internal dosimetry of choroid plexuses in nuclear medicine procedures

Choroid plexuses are vascular structures located in the brain ventricles, showing specific uptake of some diagnostic and therapeutic radiopharmaceuticals currently under clinical investigation, such as integrin-binding arginine-glycine-aspartic acid (RGD) peptides. No specific geometry for choroid plexuses has been implemented in commercially available software for internal dosimetry.The aims of the present study were to assess the dependence of absorbed dose to the choroid plexuses on the organ geometry implemented in Monte Carlo simulations, and to propose an analytical model for the internal dosimetry of these structures for ¹⁸F, ⁶⁴Cu, ⁶⁷Cu, ⁶⁸Ga, ⁹⁰Y, ¹³¹I and ¹⁷⁷Lu nuclides. A GAMOS Monte Carlo simulation based on direct organ segmentation was taken as the gold standard to validate a second simulation based on a simplified geometrical model of the choroid plexuses. Both simulations were compared with the OLINDA/EXM sphere model.The gold standard and the simplified geometrical model gave similar dosimetry results (dose difference < 3.5%), indicating that the latter can be considered as a satisfactory approximation of the real geometry. In contrast, the sphere model systematically overestimated the absorbed dose compared to both Monte Carlo models (range: 4–50% dose difference), depending on the isotope energy and organ mass. Therefore, the simplified geometric model was adopted to introduce an analytical approach for choroid plexuses dosimetry in the mass range 2–16 g. The proposed model enables the estimation of the choroid plexuses dose by a simple bi-parametric function, once the organ mass and the residence time of the radiopharmaceutical under investigation are provided.     

Assessment of MIRD data for internal dosimetry using the GATE Monte Carlo code

GATE/GEANT is a Monte Carlo code dedicated to nuclear medicine that allows calculation of the dose to organs of voxel phantoms. On the other hand, MIRD is a well-developed system for estimation of the dose to human organs. In this study, results obtained from GATE/GEANT using Snyder phantom are compared to published MIRD data. For this, the mathematical Snyder phantom was discretized and converted to a digital phantom of 100 × 200 × 360 voxels. The activity was considered uniformly distributed within kidneys, liver, lungs, pancreas, spleen, and adrenals. The GATE/GEANT Monte Carlo code was used to calculate the dose to the organs of the phantom from mono-energetic photons of 10, 15, 20, 30, 50, 100, 200, 500, and 1000 keV. The dose was converted into specific absorbed fraction (SAF) and the results were compared to the corresponding published MIRD data. On average, there was a good correlation (r ²>0.99) between the two series of data. However, the GATE/GEANT data were on average −0.16 ± 6.22% lower than the corresponding MIRD data for self-absorption. Self-absorption in the lungs was considerably higher in the MIRD compared to the GATE/GEANT data, for photon energies of 10–20 keV. As for cross-irradiation to other organs, the GATE/GEANT data were on average +1.5 ± 8.1% higher than the MIRD data, for photon energies of 50–1000 keV. For photon energies of 10–30 keV, the relative difference was +7.5 ± 67%. It turned out that the agreement between the GATE/GEANT and the MIRD data depended upon absolute SAF values and photon energy. For 10–30 keV photons, where the absolute SAF values were small, the uncertainty was high and the effect of cross-section prominent, and there was no agreement between the GATE/GEANT results and the MIRD data. However, for photons of 50–1,000 keV, the bias was negligible and the agreement was acceptable.     

Therapy of ankylosing spondylitis with 224Ra-radium chloride: dosimetry and risk considerations

Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease which reduces the quality of life and leads to disability in approximately one-third of the patients. The spectrum of therapeutic modalities is limited. The renaissance of the use of (224)Ra-radium chloride for AS treatment, however, gives rise to concern which should result in the reconsideration of (224)Ra dosimetry and in the discussion of the risks associated with this treatment. The present study introduces new dosimetric calculations for alpha and beta/gamma rays performed according to the model proposed by the International Commission on Radiological Protection (ICRP). After a treatment schedule of 10 intravenous injections, each with 1 MBq of (224)Ra, the absorbed doses were calculated to be highest on the bone surface of the patient (4.4 Gy) with a resulting effective dose of 2.5 Sv.     

Age-dependent inhalation doses to members of the public from indoor short-lived radon progeny

The main contribution of radiation dose to the human lungs from natural exposure originates from short-lived radon progeny. In the present work, the inhalation doses from indoor short-lived radon progeny, i.e., ²¹⁸Po, ²¹⁴Pb, ²¹⁴Bi, and ²¹⁴Po, to different age groups of members of the public were calculated. In the calculations, the age-dependent systemic biokinetic models of polonium, bismuth, and lead published by the International Commission on Radiological Protection (ICRP) were adopted. In addition, the ICRP human respiratory tract and gastrointestinal tract models were applied to determine the deposition fractions in different regions of the lungs during inhalation and exhalation, and the absorption fractions of radon progeny in the alimentary tract. Based on the calculated contribution of each progeny to equivalent dose and effective dose, the dose conversion factor was estimated, taking into account the unattached fraction of aerosols, attached aerosols in the nucleation, accumulation and coarse modes, and the potential alpha energy concentration fraction in indoor air. It turned out that for each progeny, the equivalent doses to extrathoracic airways and the lungs are greater than those to other organs. The contribution of ²¹⁴Po to effective dose is much smaller compared to that of the other short-lived radon progeny and can thus be neglected in the dose assessment. In fact, 90 % of the effective dose from short-lived radon progeny arises from ²¹⁴Pb and ²¹⁴Bi, while the rest is from ²¹⁸Po. The dose conversion factors obtained in the present study are 17 and 18 mSv per working level month (WLM) for adult female and male, respectively. This compares to values ranging from 6 to 20 mSv WLM^?1 calculated by other investigators. The dose coefficients of each radon progeny calculated in the present study can be used to estimate the radiation doses for the population, especially for small children and women, in specific regions of the world exposed to radon progeny by measuring their concentrations, aerosol sizes, and unattached fractions.     

Thermoluminescence characteristics of calcite with a Gaussian process regression model of machine learning

Thermoluminescence (TL) is defined as a luminescence phenomenon that can be detected when an insulator or semiconductor is thermally stimulated. Defective crystals store radiation until they are stimulated. Thermoluminescence is a method of monitoring the absorbed dose of dosimeters. The irradiation crystal is heated to 500°C to display the absorbed dose as a luminescent light. The TL dosimetric properties of calcite obtained from nature were investigated in this study. Machine learning was also examined using Gaussian process regression (GPR) for stimulated TL characteristics. According to the experimental output, the TL glow curve had two main peaks located at 90°C and 240°C with good dosimetric properties. In the four regression models of GPR, the data for the heating rate of 3°C s⁻¹ have the lowest residual.