Intercomparison of dose enhancement ratio and secondary electron spectra for gold nanoparticles irradiated by X-rays calculated using multiple Monte Carlo simulation codes.

PURPOSE: Targeted radiation therapy has seen an increased interest in the past decade. In vitro and in vivo experiments showed enhanced radiation doses due to gold nanoparticles (GNPs) to tumors in mice and demonstrated a high potential for clinical application. However, finding a functionalized molecular formulation for actively targeting GNPs in tumor cells is challenging. Furthermore, the enhanced energy deposition by secondary electrons around GNPs, particularly by short-ranged Auger electrons is difficult to measure. Computational models, such as Monte Carlo (MC) radiation transport codes, have been used to estimate the physical quantities and effects of GNPs. However, as these codes differ from one to another, the reliability of physical and dosimetric quantities needs to be established at cellular and molecular levels, so that the subsequent biological effects can be assessed quantitatively. METHODS: In this work, irradiation of single GNPs of 50 nm and 100 nm diameter by X-ray spectra generated by 50 and 100 peak kilovoltages was simulated for a defined geometry setup, by applying multiple MC codes in the EURADOS framework. RESULTS: The mean dose enhancement ratio of the first 10 nm-thick water shell around a 100 nm GNP ranges from 400 for 100 kVp X-rays to 600 for 50 kVp X-rays with large uncertainty factors up to 2.3. CONCLUSIONS: It is concluded that the absolute dose enhancement effects have large uncertainties and need an inter-code intercomparison for a high quality assurance; relative properties may be a better measure until more experimental data is available to constrain the models.

Validation of the French national health insurance information system as a tool in vaccine safety assessment: application to febrile convulsions after pediatric measles/mumps/rubella immunization.

In the French national health insurance information system (SNIIR-AM), routine records of health claimed reimbursements are linked to hospital admissions for the whole French population. The main focus of this work is the usability of this system for vaccine safety assessment programme. Self-controlled case series analyses were performed using an exhaustive SNIIR-AM extraction of French children aged less than 3 years, to investigate the relationship between MMR immunization and children hospitalizations for febrile convulsions, a well-documented rare adverse event, over 2009-2010. The results suggest a significant increase of febrile convulsions during the 6-11 days period following any MMR immunization (IRR=1.49, 95% CI=1.22, 1.83; p=0.0001) and no increase 15-35 days post any MMR immunization (IRR=1.03, 95% CI=0.89, 1.18; p=0.72). These results are in accordance with other results obtained from large epidemiologic studies, which suggest the usability of the SNIIR-AM as a relevant database to study the occurrence of adverse events associated with immunization. For future use, results associated with risk of convulsion during the day of vaccination should nevertheless be considered with particular caution.

Subcellular localization of gadolinium injected as soluble salt in rats: a microanalytical study.

The rare earth gadolinium (Gd) is used in modern industry. Solubilized DTPA Gd and DOTA Gd complexes are used as contrast media in nuclear magnetic resonance imaging. In order to determine the subcellular localization of Gd, rats were injected intraperitoneally with Gd nitrate. Two microanalytic methods, ion microanalysis and electron microprobe, enabled the distribution and the intracellular localization of Gd to be determined in the liver, spleen, bone marrow, kidneys and lung. The results showed: a) a punctual distribution of Gd in the tissues (liver, spleen, bone marrow and lung) as observed by ion microscopy; b) a selective concentration of Gd in the lysosomes of macrophages of the liver (hepatocytes), spleen (macrophages), bone marrow (macrophages) and lung (phagocyte cells), as determined by electron probe X-ray microanalysis. In all these sites the Gd is associated to phosphorus. Results are compared to those found for other rare earths and metal elements.