Possibilities and limitations of in-vivo dosimetry

A survey is given of the practical problems, limitations and potential of in vivo dose measurements. Practical problems related to the use of build-up material for entrance dose measurements, the lack of backscatter for exit dose determination and the derivation of the target absorbed dose from entrance and exit dose values, are summarized. The limitations of the dosimetry systems, such as the frequency of calibration and the large number of correction factors, have been elucidated. A number of groups applying in vivo dosimetry have detected serious errors in the dose delivery to patients. Part of these errors are human mistakes in the setup of the patient, of beam modifying devices and of wrong machine settings. Systematic errors in the irradiation procedure have also been detected with in vivo dose measurements. These errors were related to machine performance, the dose calculation procedure and the patient set-up. For all these applications it has been shown that in vivo dosimetry is a useful tool in the quality assurance programme of a radiotherapy department. (author). 9 refs, 8 figs, 3 tabs