Variability analysis of SAR from 20 MHz to 2.4 GHz for different adult and child models using finite-difference time-domain.

This paper deals with the variability of body models used in numerical dosimetry studies. Six adult anthropomorphic voxel models have been collected and used to build 5-, 8- and 12-year-old children using a morphing method respecting anatomical parameters. Finite-difference time-domain calculations of a specific absorption rate (SAR) have been performed for a range of frequencies from 20 MHz to 2.4 GHz for isolated models illuminated by plane waves. A whole-body-averaged SAR is presented as well as the average on specific tissues such as skin, muscles, fat or bones and the average on specific parts of the body such as head, legs, arms or torso. Results point out the variability of adult models. The standard deviation of whole-body-averaged SAR of adult models can reach 40%. All phantoms are exposed to the ICNIRP reference levels. Results show that for adults, compliance with reference levels ensures compliance with basic restrictions, but concerning children models involved in this study, the whole-body-averaged SAR goes over the fundamental safety limits up to 40%.

Metastases of human tumor xenografts in nude mice.

In the present study, using systematic microscopic examination, we tried to determine the true incidence of metastases in nude mice bearing a wide variety of human tumors. A total of 63 malignant tumors were successfully transplanted subcutaneously and 831 nude mice bearing tumors were examined. It appeared that 17 of the 63 tumors (26.9%) retained their metastatic ability in nude mice. Most of these tumors were adenocarcinomas (11/17 cases). Generally the metastatic deposits in the lungs and, to a lesser extent, in the lymph nodes were small and thus only detectable on microscopic examination. We also found a positive correlation between the presence of metastases and neoplastic infiltration of the lymphatic and/or blood vessels around the subcutaneous tumors. Metastatic human tumors, including neoplastic cells from effusion, exhibited higher metastatic ability than primary tumors (p less than 0.005). However, the expression of this metastatic potential depends on several factors including tumor volume, survival time after inoculation and murine hepatitis infection. Thus, animals with metastases bore larger tumors (9.56 cm3) than those without metastasis (6.35 cm3; p less than 0.0001). Moreover, survival time after inoculation was longer in mice with metastases (104 days) than in mice without metastases (81 days; p less than 0.0001). A negative influence of viral hepatitis on the incidence of metastases was observed. This may simply be related to the shortened life span of the animals. Death due to this infection may precede the expression of the metastatic potential.