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PubMed2004

Adult female voxel models of different stature and photon conversion coefficients for radiation protection.

This paper describes the construction of three adult female voxel models, two whole-body and one from head to thighs, from computed tomographic data of 3 women of different stature. Voxel models (also called phantoms) are human models based on computed tomographic or magnetic resonance images obtained from high resolution continuous scans of a single individual. The gray-scale data or information content of the medical images are interpreted into tissues (i.e., organs), a process known as segmentation. The phantoms, consisting of millions of volume elements, called voxels, provide a three-dimensional representation of the human body and the spatial form of its constituent organs and structures. They were initially developed for radiation protection purposes to estimate the organ and effective doses and hence the risk to a person or population due to an irradiation. This paper also presents conversion coefficients for idealized geometries of external photon exposures of energies 10 keV-1 MeV for the three female models, calculated with a Monte Carlo code. Until now there were not any published data on conversion coefficients for explicit female voxel models. Such sets of conversion coefficients exist for voxel adult males or for MIRD-type male, female, and hermaphrodite models. Numerical differences of the calculated conversion coefficients for the voxel female models and MIRD-type models can amount up to 60% or more for external exposures and are due to the improved anatomical realism of the voxel models. The size of the model also has an effect on the conversion coefficients, particularly for deeper lying organs and energies below 200 keV. The three separate sets of conversion coefficients allow one to choose the most suitable model according to the size of the individual as well as to study the dosimetric variations due to the size of the model.

Adult↗
PubMedDate not supplied

Thermal stress and radiation protection principles.

Exposure to radiofrequency (RF) fields can occur in residential, occupational and medical settings. Since many technologies use RF fields, it is important to fully investigate their effects on the human body. Since the demonstrated effect of RF exposure is heating, it is important to critically evaluate studies of elevated temperature effects on the human body, from the cellular and tissue level to the whole body level, including potential effects on the susceptible groups such as the very young and the very old. WHO convened a Workshop in the Spring of 2002 on the subject of Adverse Temperature Levels in the Human. The goal of the workshop was to evaluate most recent data useful for the development of science-based RF exposure limits. This paper outlines radiation protection principles that underline such an evaluation. It discusses the quality of literature needed for sound scientific reviews, provides the hierarchy of scientific evidence used to establish effects, distinguish between biological effects and adverse health consequences and indicates how evidence is evaluated. In addition, criteria for determining the most sensitive effects, the value of an effect that has a dose-response and methods of extrapolation are also described. Finally, the need to account for scientific uncertainty in the formulation of guidance on exposure is discussed.

Dose-Response Relationship, Radiation↗