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Chronic cigarette smoking leads to changes in the respiratory tract that might affect the dose received from exposure to radon progeny. In this study, changes induced by cigarette smoking in the respiratory tract were collected from the literature and used for calculation of the dose received by the lungs and organs outside the respiratory tract. Morphological and physiological parameters affected by chronic smoking were implemented in the human respiratory tract model (HRTM) used by the International Commission of Radiological Protection (ICRP). Smokers were found to receive lung doses 3% smaller than the ICRP reference worker (non-smoking reference adult male) in mines and 14% smaller in indoor workplaces and tourist caves. A similar dose reduction was found for the extrathoracic region of the HRTM. Conversely, kidneys, brain, and bone marrow of smokers were found to receive from 2.3- up to 3-fold of the dose received by the respective organ in the ICRP reference worker, although they remained at least two orders of magnitude smaller than the lung dose. These results indicate that the differences in the lung dose from radon progeny exposure in cigarette smokers and non-smokers are smaller than 15%.

The increasing use of new radiopharmaceuticals invites us to reconsider some radiation protection issues, such as the contact restriction time that limits public exposure by nuclear medicine patients. Contact restriction time should be patient specific and conservative, and its assessment made easy for clinicians. Here a method is proposed based on conservative estimation of the whole-body retention function and at least one measurement of the patient’s dose rate. Recommended values of the retention function are given for eight therapies: 131I (Graves’ disease, remnant ablation, patient follow-up, meta-iodobenzylguanidine), 177Lu-prostate-specific membrane antigen and 177Lu-DOTATATE therapies, and 90Y and 166Ho microsphere injection of the liver. The patient line source model for scaling dose rate from one distance to another is included in the restriction time calculation. The method is benchmarked against published values and the influence of the dose rate scaling and whole-body retention function illustrated. A spreadsheet is provided, along with the source code, with recommended values for the eight therapies. The recommended values can be changed as well as the dose rate scaling function, and other radiopharmaceuticals can be included in the spreadsheet provided retention functions are defined.

Objective. Molecular radiotherapy is the most used treatment modality against malign and benign diseases of thyroid. In that context, the large heterogeneity of therapeutic doses in patients and the range of effects observed show that individualized dosimetry is essential for optimizing treatments according to the targeted clinical outcome. Approach. We developed a high-resolution mobile gamma camera specifically designed to improve the quantitative assessment of the distribution and biokinetics of 131I at patients’s bedside after treatment of thyroid diseases. The first prototype has a field of view of 5×5 cm2 and consists of a high-energy parallel-hole collimator made of 3D-printed tungsten, coupled to a 6 mm thick CeBr3 scintillator readout by an array of silicon photomultiplier detectors. The intrinsic and overall imaging performance of the camera was evaluated with 133Ba and 131I sources. In order to test its quantification capability in realistic clinical conditions, two different 3D-printed thyroid phantoms homogeneously filled with 131I were used. Both single view and conjugate view approaches have been applied, with and without scatter correction technique. Main Results. The camera exhibits high imaging performance with an overall energy resolution of 7.68±0.01%, a submillimetric intrinsic spatial resolution of 0.74±0.28 mm and a very low spatial distortion 0.15±0.10 mm. The complete calibration of the camera shows an overall spatial resolution of 3.14±0.03 mm at a distance of 5 cm and a corresponding sensitivity of 1.23±0.01 cps/MBq, that decreases with distance and slightly changes with source size, due to the influence of scattering. Activity recovery factors better than 97% were found with the thyroid phantoms. Significance. These preliminary results are very encouraging for the use of our camera as a tool for accurate quantification of absorbed doses and currently motivates the development of a fully operational clinical camera with a 10×10 cm2 field of view and improved imaging capabilities.

International audience; To further improve the understanding of in vitro biological effects of incorporated radionuclides, it is essential to accurately determine cellular absorbed doses. In the case of β emitters, the cross-dose is a major contribution, and can involve up to millions of cells. Realistic and efficient computational models are needed for that purpose. Conventionally, distances between each cell are calculated and the related dose contributions are cumulated to get the total cross-dose (standard method). In this work, we developed a novel approach for the calculation of the cross-absorbed dose, based on the use of the radial distribution function (rdf)) that describes the spatial properties of the cellular model considered. The dynamic molecular tool LAMMPS was used to create 3D cellular models and compute rdfs for various conditions of cell density, volume size, and configuration type (lattice and randomized geometry). The novel method is suitable for any radionuclide of nuclear medicine. Here, the model was applied for the labeling of cells with 18F-FDG used for PET imaging, and first validated by comparison with other reference methods. Mean Scross values calculated with the novel approach versus the standard method agreed very well (relative differences less that 0.1%). Implementation of the rdf -based approach with LAMMPS allowed to achieved results considerably faster than with the standard method, the computing time decreasing from hours to seconds for 106 cells. The rdf -based approach was also faster and easier to accommodate more complex cellular models than the standard and other published methods. Finally, a comparative study of the mean Scross for different types of configuration was carried out, as a function of the cell density and the volume size, allowing to better understand the impact of the configuration on the cross-absorbed dose

International audience; In the case of a nuclear reactor accident the release contains a high proportion of iodine-131 that can be inhaled or ingested by members of the public. Iodine-131 is naturally retained in the thyroid and increases the thyroid cancer risk. Since the radiation induced thyroid cancer risk is greater for children than for adults, the thyroid dose to children should be assessed as accurately as possible. For that purpose direct measurements should be carried out with age-specific calibration factors but, currently, there is no age-specific thyroid phantoms allowing a robust measurement protocol. A set of age-specific thyroid phantoms for 5, 10, 15 year old children and for the adult has been designed and 3D printed. A realistic thyroid shape has been selected and material properties taken into account to simulate the attenuation of biological tissues. The thyroid volumes follow ICRP recommendations and the phantoms also include the trachea and a spine model. Several versions, with or without spine, with our without trachea, with or without age-specific neck have been manufactured, in order to study the influence of these elements on calibration factors. The calibration factor obtained with the adult phantom and a reference phantom are in reasonable agreement. In vivo calibration experiments with germanium detectors have shown that the difference in counting efficiency, the inverse of the calibration factor, between the 5 year and adult phantoms is 25% for measurement at contact. It is also experimentally evidenced that the inverse of the calibration factor varies linearly with the thyroid volume. The influence of scattering elements like the neck or spine is not evidenced by experimental measurements. © 2017 Institute of Physics and Engineering in Medicine.

International audience; Positron emission tomography (PET) offers an effective method for tracking β+ emitters-labeled cells in vivo. However, in vitro high labelling activities used may cause cell damage or death. Our understanding of the impact of such procedure remains limited by the fact that the biological effects are usually linked to the activity per cell rather than the absorbed dose. To assess the dose delivered to the cells during the radiolabelling, a multi-cellular dosimetry computational tool was developed, allowing the study of two key parameters the cell density and the labelling efficiency. Through a hybrid method based on Monte Carlo simulations (MCNP6 code) and an analytical approach implemented in Python, the mean absorbed dose received by a target cell was calculated for distributions with a very large number of cells - up to hundreds of millions. An advanced investigation of in vitro cell labelling with β-emitting radionuclides was carried out via (i) a systematic study of the effects of the labelling parameters on the cell absorbed dose for18F,64Cu and68Ga, and (ii) a quantitative comparison between cellular and conventional dosimetry. The results provided a thorough analysis of how the dose (self, cross and extracellular medium dose contributions) varies with the initial labelling parameters selected and highlighted the conditions where the cellular dosimetry is required over the conventional dosimetry. The dosimetric model was finally applied to real conditions of 18F-FDG labelling on the basis of eight reported studies. The results showed that similar activity per cell can lead to significantly different absorbed dose and pointed out differences between cellular and conventional dosimetry up to a factor of 5. © 2019 Institute of Physics and Engineering in Medicine.

In order to best cover the possible extent of heights and weights of male adults the construction of 25 whole body 3D models has been undertaken. Such a library is thought to be useful to specify the uncertainties and relevance of dosimetry calculations carried out with models representing individuals of average body heights and weights. Representative 3D models of Caucasian body types are selected in a commercial database according to their height and weight, and 3D models of the skeleton and internal organs are designed using another commercial dataset. A review of the literature enabled one to fix volume or mass target values for the skeleton, soft organs, skin and fat content of the selected individuals. The composition of the remainder tissue is fixed so that the weight of the voxel models equals the weight of the selected individuals. After mesh and NURBS modelling, volume adjustment of the selected body shapes and additional voxel-based work, 25 voxel models with 109 identified organs or tissue are obtained. Radiation transport calculations are carried out with some of the developed models to illustrate potential uses. The following points are discussed throughout this paper: - justification of the fixed or obtained models’ features regarding available and relevant literature data; - workflow and strategy for major modelling steps; - advantages and drawbacks of the obtained library as compared with other works. The construction hypotheses are explained and justified in detail since future calculation results obtained with this library will depend on them.

cited By 7; This paper addresses the question of the morphological dependence of counting efficiency curves for in vivo lung monitoring of workers, with a particular focus on the case of female workers for whom different chest girth and cup size are considered. A library of 24 female torsos, with chest girth varying from 85 to 120 and cup size from A to F, was constructed usingmesh and NURBS formats. The anatomical ealism and usefulness of these models for simulating in vivo countingmeasurements are illustrated and simulations are reported for a typical 4-germanium (Ge) counting system. A simple analytic formula describing the relation between efficiency curves obtained for each female phantom is given. This formula uses the mass attenuation coefficient for adipose tissue and two parameters which are dependant on lung volume and breast weight. The model is tested against Monte Carlo simulated data, experimental data obtained with the Livermore phantom and published data. The model correctly describes the efficiency curve and, since the parameters depend on the counting geometry, it is shown how to estimate them from experimental measurements. © 2010 Institute of Physics and Engineering in Medicine.