Techniques used for in-vivo dosimetry

Two methods, diodes and port films, used for in vivo dosimetry are discussed. The response of the diodes in calibrated by comparison with an ionization chamber in a phantom. This calibration procedure has to be performed both for entrance and exit dose measurements. For obtaining optimal accuracy the influence on diode response of different parameters are also investigated, mainly that of temperature, dose rate, collimator opening and source - skin - distance. A method is presented to derive target doses from measured entrance and exit doses. The second method investigated is based on the use of conventional port films. The possibilities for deriving exit dose distributions from optical density profiles are evaluated. These exit dose distributions derived from port films are compared to ionometric distributions obtained at the exit of a phantom with large inhomogeneities in quasi full backscatter conditions. The port film method looks very promising as the deviation between the two methods is typically of the order of one or two percent. (author). 5 refs, 12 figs