[Practical determination of volume and doses in conformal radiotherapy]

The determination of the target volumes and the dose to be delivered are critical medical steps in order to locally control the disease and to limit the risks of normal tissues injury. While many clinical situations are compatible with standardised technique and beam arrangements, the tools provided by modern medical diagnostic imaging procedures and tridimensional dosimetry allow an improved conformation of the irradiated volume and the administered dose to the clinical target volume. However, this approach requires an increased precision in tumour and normal tissues delineation, based on patient immobilisation devices, standardisation of mobile organs repletion status and image acquisition procedures, explicit definition of the biological and physical safety margins, definition of acceptable levels of dose heterogeneity in the planning target volume and appropriate quality assurance procedures.