Assessment of patient exposure in nuclear medicine

The radiation exposure of a patient in diagnostic nuclear medicine is influenced by different factors, which may be separated into direct and indirect determinants of exposure. The radiation burden is directly related to the radionuclide used (beta, gamma radiation, energy of radiation, physical half-life) and the activity used. In addition, the radiation exposure is strongly influenced by the type of radiolabelled compound (radiopharmaceutical) and its metabolic behaviour. The metabolism of a radiopharmaceutical, however, depends not only on the general principles of its biodistribution but also on individual parameters of its biokinetics (i.e. patient's age, sex, weight, organ uptake and excretion). Optimisation in radiation protection requires a careful selection of activity, radionuclide and radiopharmaceutical compound for a patient. The radiation exposure of a patient may be influenced considerably by disturbance factors which can be controlled by means of quality assurance measures. Concerning the radiopharmaceutical, radiochemical and chemical impurities have to be ruled out before administration. Activity meters and gamma cameras must be checked by appropriate quality control procedures. The check of the gamma cameras includes background, efficiency, uniformity, linearity and resolution and has to be an integral part of a routine quality control programme in a nuclear medicine department.