[en] Due to the low energies of Auger electrons and the correspondingly short distance they travel (of the order of 1 nm to 1 μm), the biological effects of Auger emitters are highly dependent upon their cellular and subcellular distribution. Auger emitters that localise within the cell nucleus and bind to DNA produce effects similar to high LET radiations, in contrast to the low LET type effects seen with emitters present in the cell cytosol or other extranuclear sites. Conventional organ dosimetry will give an estimate of average dose delivered to all cell nuclei in an organ but may strongly underestimate the actual dose, either to all nuclei, in the case of Auger emitters which concentrate in the cell nucleus, or to only some nuclei, in the case of cell-cell heterogeneity in uptake. Where better estimates of the biological risk associated with internal contamination by Auger-emitting radionuclides are required, organ dose should be modified according to the subcellular distribution of the radionuclide or cellular dosimetry methods used. Radionuclides used in diagnostic medical applications present a significant source, in terms of dose to the individual, of exposure to Auger emitters. Under normal circumstances, human exposure to Auger electron-emitting radionuclides in the environment is at very low levels. (author)

[en] In the aim to propose recommendations, simulations were performed for restricting the radiation hazards to the family and the members of the public coming into contact with a patient treated with ¹³¹I for a thyroid pathology. The simulated dose constraints were 1 mSv for the children, 3 mSv and 5 mSv for the adults (family and close friends), and 0,3 mSv and 1 mSv for the members of the public. Several contact patterns were tested: daily visits, public transports, return to work, sleeping with partner and close contact with children. The recommendations duration was evaluated both as a function of the administrated activity (out-patient) or the residual activity (discharged in-patient) by measuring the dose rate at 1 m distance from the patient. Daily visits at home from a close friend can last 3 hours, without the visitor receives a radiation dose exceeding 1 mSv, if the distance between the patient and the visitor is higher than 1 m. It is unnecessary to recommend restrictions on the use of public transport, except in the case of transport longer than 2 hours on the day of leaving the hospital depending on residual activity. For return to work recommendations are given. For partners, the main exposition occurs during the night, and recommendation to use separate rooms during a period of time depending on residual activity is given. Patient should be advised to refrain from close contact with children and pregnant women during a period of time depending on the residual activity. Particular consideration needs to be given to children aged 6 years or younger. Dose constraint values of 0,3 mSv for the members of the public and 3 mSv for close friends can lead to very restrictive recommendations. On the other hand, dose constraint values of 1 mSv for the members of the public and 5 mSv for close friends seams to be a better compromise for a reasonable radiation hazards of the family and the members of the public. (authors)

[en] The evaluation of biological risks, associated to the internal administration of diagnostic radiopharmaceutical, lies in the calculation of the mean absorbed dose to target organs. This conventional dosimetric method assumes an uniform distribution of radioactivity and absorbed dose within organs. Following this approach, dosimetry assessment is a prerequisite for any clinical use of a radiopharmaceutical. The absorbed dose remains within very low values, because of the short residence time of radiotracers in biological tissues, the injected activity (less than 740 MBq), and the energy emitted per nuclear transition, which makes them suitable for human use. No adverse radiation effect on target organs has been described, provided that safety limits are not trespassed and that elementary precautions are taken.

[en] To study the absorbed dose due to the electronic rays of Tc ⁹⁹m, an analytic fit of the Scaled Dose Point Kernel Function F(x) was evaluated. Using this fit, the percentage of the whole energy delivered to the medium in a sphere centered on the point source was computed. In the case of Tc ⁹⁹m, the major contribution of the low energetic electronic rays (<2kev) is emphasized. These rays induce the deposit of 15% of the whole energy delivered by the electrons, in a very small volume (sphere with a 0.05μm radius). Classical evaluation may underestimate the absorbed dose by a 10⁵ scale factor in Tc ⁹⁹m colloid liver uptake

[en] The recent introduction of hybrid systems combining a SPECT and a CT in nuclear medicine, greatly improved the diagnostic accuracy for particular clinical indications, due to the possible attenuation and/or scatter correction of the SPECT functional images and the availability of helpful anatomic information. Although the gamma cameras performances are noticeably comparable, the associated CT furnished by the manufacturer are relatively different from each other. Whatever the system is, the introduction of CT in the nuclear diagnostic process results in a significant increase of the patient dose. This dose increase should be justified and optimized considering both the clinical question and the CT settings available on these systems. The installation of a hybrid system must be accompanied by the management of a documentary quality insurance program, jointly developed by the technologists, physicists and physicians, both covering its clinical use and the associated dosimetry issues as monitoring its performances. Particular quality control procedures have to be defined because of the coupling between the two devices. (authors)

[en] The radiation dose rate delivered by electron emissions of ^99mTc, ¹²³I, ¹¹¹In, ⁶⁷Ga and ²⁰¹Tl was evaluated at the subcellular level. Spherical models of sources were used to simulate various cellular localizations of radionuclides. These models were applied to large lymphocytes, assuming uniform distributions of radioactivity throughout the nucleus, the cytoplasm or the cell membrane surface. The graphs of the absorbed dose rate plotted according to the distance from the center of the cell show that the dose rate strongly depends on the subcellular distribution of the radioisotope. The absorbed dose rate D(O) at the center of the cell delivered by a constant cellular radioactivity of ^99mTc, ¹²³I, ¹¹¹In, ⁶⁷Ga and ²⁰¹Tl is respectively 94, 21, 18, 74 and 76 times higher if the radioactivity is localized within the cell nucleus than if it is situated only on the cell membrane. D(O) for subcellular localizations was compared to D(O) obtained by assuming uniform distribution of radioactivity throughout the cell. This latter assumption may underestimate the dose rate from 2.8- to 3.2-fold if the tracer is exclusively localized within the nucleus or overestimate from 4.3- to 30-fold if the tracer is localized within the cytoplasm or on the cell membrane, depending on the radionuclide. Such findings show that the localization of radiopharmaceuticals at the subcellular level plays a crucial role in determining the actual dose delivered to the cell nucleus in diagnostic nuclear medicine procedures. 27 refs., 4 figs., 4 tabs

[en] After having briefly recalled the nuclear medicine principles and objectives, and the main radiations used for different purposes (positrons for diagnosis, photons for diagnosis, electrons for therapy or diagnosis), the author presents the principle of determination of the absorbed dose: how this dose is expressed, how it is calculated per cumulative activity unit, how cumulative activity is determined. Then, she discusses some practical aspects of dosimetric assessments during diagnosis or therapeutic examinations

[en] This paper reviews the published data relating to radiation hazards to the family and close friends or the members of the public, associated with nuclear medicine patients. The new annual dose limit of 1 mSv proposed by the ICRP for members of the public and the concept of dose constraints should modify the French legislation and the radioprotection guidance. Dose constraints are set prospectively and are not expected to be exceeded. They are no legal dose limits. They can be higher in the case of the family and close friends than the dose limit of 1 mSv. The European Commission proposes dose constraints values of 3 mSv for the family and close friends (adults) and 0.3 mSv for the members of the public, as the United Kingdom's recommendations are respectively 5 mSv and 1 mSv. For diagnostic studies, the quantities of radioactivity currently administered do not necessitate any special precautions or restrictions to be place on the patient. The main exception was found in the situation of an out patient given ¹¹¹In who had to look after a fretful infant with close contact time of 9 hours per day. For breast-feeding, comprehensive set of recommendations, including no interruption or interruption during only a few hours were proposed to ensure that the effective dose to the infant does not exceed 1 mSv. Nevertheless, as a precaution, breast-feeding interruption should be recommended, whatever the radiopharmaceutical, or if possible, to defer the medical exploration. The main radiation protection problem occurs for therapeutic treatment with gamma ray emitters such as ¹³¹I for the treatment of thyroid pathology. There is a range of published recommendations for limiting the exposure of close friends and the members of the public. These advises include private and public transports, return to work, sleeping with partner and close contact with children. The recommendations proposed by the European Commission for the members of the public are quite restrictive if compared with the British recommendations. For instance, the European Commission instruction is that travelling by public transport should be restricted to about two hours per trip, the first week. The recommendation occurs whatever the administered activity. As the British guidance indicates that it is extremely unlikely that any person could receive a radiation dose exceeding 0.3 mSv as a result of travelling with a patient released from hospital with a residual activity of less than 800 MBq of iodine 131. It is therefore unnecessary to recommend restrictions on the use of public transport, except in the case of transport longer than 3 hours on the day of leaving the hospital. For partners, the main exposition occurs during the night, and recommendation to use separate rooms during a period of time depending on residual activity has been proposed. Patient should be advised to refrain from close contact with children and pregnant women during a period of time depending on the residual activity. Particular consideration needs to be given to children aged 3 years or younger. Considering the discrepancies between the published radioprotection guidances, it is very important that the French nuclear medicine community proposes dose constraints values and its own recommendations. (author)

[en] In the classical dosimetry one supposes a uniform distribution of the radio-pharmaceuticals at the source organ level as well as a homogeneous distribution of the absorbed dose. This hypotheses are not always verified in biology, and the influence of the tracer localisation on the dose delivered at the cellular nucleus has been studied. The average dose delivered by the electron emission of different radio-isotopes used in diagnosis has been calculated by taking into account the radioactivity localized upon the target cell (Dself), and upon the neighbouring cells (Dcross). Nuclear, cytoplasmic and membranous localizations of the tracer were simulated for different cellular sizes. In the particular case of ^99mTc and cells of nuclear radius about 4 μm and cellular radios about 8 μ, Dcross is independent of the intra-cellular localisation of the tracer. On the contrary, for a nuclear localisation Dself is 52 and 157 times more important than for the cytoplasmic and membranous localisation, respectively. The dose at the cellular nucleus due to electron emission of ^99mTc is under-estimated by a factor 2.6 by classical dosimetry when the radioactivity is nuclear. On the contrary, the classical model over-estimates by a factor 1.2 the dose at nucleus for cytoplasmic and membranous localizations. This study shows that the dose delivered at cellular nucleus by the electron emissions of ^99mTc depends on the localisation of the tracer. The modelling proposed allows a better evaluation of the radiobiological hazards related to the administration of radiopharmaceuticals in diagnostic nuclear medicine

[en] The mean dose delivered to the cell nucleus by electron emissions of ⁹⁹Tc^m, ¹²³I, ¹¹¹In, ⁶⁷Ga and ²⁰¹Tl was evaluated at the subcellular level. Models were applied assuming uniform distributions of radioactivity throughout the nucleus, the cytoplasm or the cell membrane, allowing computation of the total absorbed fraction φ and S-values to the cell nucleus as a function of cell dimensions. The graphs of φ plotted according to cell dimensions show that the dose to the cell nucleus strongly depends on the subcellular distribution of radioactivity, the nucleus radius R_nucl and the cytoplasmic thickness e. To ease future calculations, third-degree polynomials have been separately fitted to the relationship between the mean absorbed dose to the nucleus for activity accumulated in the nucleus, cytoplasm or surface of the cell membrane. We found a good agreement between our computations and the values obtained by the polynomials. The relative difference between the two methods is always less than 0.7%, 2.8% and 4.5% respectively for nuclear, cell membrane and cytoplasmic distributions. (author)