Individual monitoring of internal exposure for nuclear medicine workers in Switzerland.

Monitoring of internal exposure for nuclear medicine workers requires frequent measurements due to the short physical half-lives of most radionuclides used in this field. The aim of this study was to develop screening measurements performed at the workplace by local staff using standard laboratory instrumentation, to detect whether potential intake has occurred. Such measurements do not enable to determine the committed effective dose, but are adequate to verify that a given threshold is not exceeded. For radioiodine, i.e. (123)I, (124)I, (125)I and (131)I, a calibrated surface contamination monitor is placed in front of the thyroid to detect whether the activity threshold has been exceeded. For radionuclides with very short physical half-lives (≤6 h), such as (99m)Tc and those used in positron emission tomography  imaging, i.e. (11)C, (15)O, (18)F and (68)Ga, screening procedures consist in performing daily measurements of the ambient dose rate in front of the abdomen. Other gamma emitters used for imaging, i.e. (67)Ga, (111)In and (201)Tl, are measured with a scintillation detector located in front of the thorax. For pure beta emitters, i.e. (90)Y and (169)Er, as well as beta emitters with low-intensity gamma rays, i.e. (153)Sm, (177)Lu, (186)Re and (188)Re, the procedure consists in measuring hand contamination immediately after use. In Switzerland, screening procedures have been adopted by most nuclear medicine services since such measurements enable an acceptable monitoring while taking into account practical and economic considerations.

A new method for the determination of plutonium and americium using high pressure microwave digestion and alpha-spectrometry or ICP-SMS

Plutonium and americium are radionuclides particularly difficult to measure in environmental samples because they are alpha-emitters and therefore necessitate a careful separation before any measurement, either using radiometric methods or ICP-SMS. Recent developments in extraction chromatography resins such as Eichrom (R) TRU and TEVA have resolved many of the analytical problems but drawbacks such as low recovery and spectral interferences still occasionally occur. Here, we report on the use of the new Eichrom (R) DGA resin in association with TEVA resin and high pressure microwave acid leaching for the sequential determination of plutonium and americium in environmental samples. The method results in average recoveries of 83 +/- 15% for plutonium and 73 +/- 22% for americium (n = 60), and a less than 10% deviation from reference values of four IAEA reference materials and three samples from intercomparisons exercises. The method is also suitable for measuring Pu-239 in water samples at the mu Bq/l level, if ICP-SMS is used for the measurement.

Fluorodeoxyuridine mediated cell cycle synchronization in S-phase increases the Auger radiation cell killing with 125I-iododeoxyuridine.

Aim: 125I-iododeoxyuridine is a potential Auger radiation therapy agent. Its incorporation in DNA of proliferating cells is enhanced by fluorodeoxyuridine. Here, we evaluated therapeutic activities of 125I-iododeoxyuridine in an optimized fluorodeoxyuridine pre-treatment inducing S-phase synchronization. Methods: After S-phase synchronization by fluorodeoxyuridine, cells were treated with 125I-iododeoxyuridine. Apoptosis analysis and S-phase synchronization were studied by flow cytometry. Cell survival was determined by colony-forming assay. Based on measured growth parameters, the number of decays per cell that induced killing was extrapolated. Results: Treatment experiments showed that 72 to 91% of synchronized cells were killed after 0.8 and 8 kBq/ml 125I-iododeoxyuridine incubation, respectively. In controls, only 8 to 38% of cells were killed by corresponding 125I-iododeoxyuridine activities alone and even increasing the activity to 80 kBq/ml gave only 42 % killing. Duplicated treatment cycles or repeated fluorodeoxyuridine pre-treatment allowed enhancing cell killing to >95 % at 8 kBq/ml 125I-iododeoxyuridine. About 50 and 160 decays per S-phase cells in controls and S-phase synchronization, respectively, were responsible for the observed cell killing at 0.8 kBq/ml radio-iododeoxyuridine. Conclusion: These data show the successful application of fluorodeoxyuridine that provided increased 125I-iododeoxyuridine Auger radiation cell killing efficacy through S-phase synchronization and high DNA incorporation of radio-iododeoxyuridine.

Immunociblage des tumeurs: situation et perspectives en 2000

Following 15 years of experimental studies, tumor immunotargeting using monoclonal antibodies directed against tumor associated antigens shows now important monoclonal antibodies directed against tumor associated antigens shows now important clinical developments. This is mainly due to encouraging therapeutic results which have obtained using humanized antibodies such as the anti-CD20 rituximab in follicular B lymphomas and the anti-DrbB2 herceptin in breast carcinomas. Thanks to genetic engineering it is possible to graft variable or hypervariable regions from murine antibodies to human IgG, and even to obtain fully human antibodies by using either transgenic mice containing a large part of the human repertoire of human IgG, or selection of human antibody fragments expressed by phages. Radiolabeling of antibodies played a major role to demonstrate the tumor immunotargeting specificity and remains attractive for the diagnosis by immunoscintigraphy as well as for the treatment by radioimmunotherapy of some cancers. In this review, the current results and the prospects of diagnostic and therapeutic uses of anti-tumor antibodies and their fragments will be described. Concerning diagnosis, 123-iodine or 99m-technetium labeled Fab fragments allowed very demonstrative tumor images but this technique has a limited effect upon the therapeutic attitude. Immuno-PET (positron emission tomography) could enhance the sensitivity of this imaging method. Radio-immunoguided surgery and immunophotodetection are attractive techniques still under evaluation. Concerning therapy, 131-iodine labeled anti-CD20 antibodies gave spectacular results in non-Hodgkin's B lymphomas. In solid tumors which as less radiosensitive, radioimmunotherapy could concern small tumors and need the use of two-steps targeting and/or alpha emitters radioisotopes. Some other strategies will be described such as bispecific antibodies directed against tumors and immune effector cells, some antibody fragments expressed on T cells called T-bodies or some biological studies using intrabodies. Published data and works in progress demonstrate that immunotargeting of tumors will have a growing place in the treatments of cancer patients.

Uncertainty evaluation in activity measurements using ionization chambers

Pressurized re-entrant (or 4 pi) ionization chambers (ICs) connected to current-measuring electronics are used for activity measurements of photon emitting radionuclides and some beta emitters in the fields of metrology and nuclear medicine. As a secondary method, these instruments need to be calibrated with appropriate activity standards from primary or direct standardization. The use of these instruments over 50 years has been well described in numerous publications, such as the Monographie BIPM-4 and the special issue of Metrologia on radionuclide metrology (Ratel 2007 Metrologia 44 S7-16, Schrader1997 Activity Measurements With Ionization Chambers (Monographie BIPM-4) Schrader 2007 Metrologia 44 S53-66, Cox et al 2007 Measurement Modelling of the International Reference System (SIR) for Gamma-Emitting Radionuclides (Monographie BIPM-7)). The present work describes the principles of activity measurements, calibrations, and impurity corrections using pressurized ionization chambers in the first part and the uncertainty analysis illustrated with example uncertainty budgets from routine source-calibration as well as from an international reference system (SIR) measurement in the second part.