For electron and megavoltage photon beams, Spencer-Attix cavity theory further adapted by Nahum remains the accepted standard selleck method used to convert absorbed dose in a wall-less detector to absorbed dose in the medium of interest. For several decades, the approach has been widely used in protocols to generate data for ionization chamber dosimetry. As a considerable effort was made towards accurate Monte Carlo methods,
computation techniques are nowadays available to determine absorbed dose accurately in complex geometries, including radiation detectors. In the development of nonstandard beam protocols, direct Monte Carlo dose calculations using realistic models are being suggested and used to generate data for ionization chamber dosimetry. This indicates that for a general dosimetric context, including nonstandard beams, a more general cavity theory in agreement with what is currently being done could be adopted. Not only this could be of interest in the dosimetry standards community, but also for educational purposes. This paper re-examines Spencer-Attix theory from first principles, using a new general cavity theory rigorously derived from radiation transport equations. The approach is based on the same schematization as for Spencer-Attix’s (i.e. groups of slow and fast electrons) and yields a general expression of
absorbed dose for suitably implemented Monte Carlo methods. The Spencer-Attix-Nahum formulation is shown to PD0332991 nmr be a special case of the
presented model, outlining specific issues of the standard method. By providing an expression of absorbed dose which reflects the gold standard calculation method (i.e. Monte Carlo), the proposed theory could be adopted by the radiation dosimetry community.”
“The potential antiproliferative effects of low power millimeter waves (MMWs) at 42.20 and 53.57 GHz on RPMI 7932 human skin melanoma cells were evaluated in vitro in order to ascertain if these two frequencies, comprised in the range of frequency used in millimeter wave therapy, would have a similar effect when applied in vivo to malignant melanoma tumours. Cells were exposed for 1 h exposure/day selleck inhibitor and to repeated exposure up to a total of four treatments. Plane wave incident power densities < 1 mW/cm(2) were used in the MMWs-exposure experiments so that the radiations did not cause significant thermal effects. Numerical simulations of Petri dish reflectivity were made using the equations for the reflection coefficient of a multilayered system. Such analysis showed that the power densities transmitted into the aqueous samples were a parts per thousand currency sign0.3 mW/cm(2). Two very important and general biological endpoints were evaluated in order to study the response of melanoma cells to these radiations, i.e. cell proliferation and cell cycle.