ABSTRACT
Gross tumor volume (GTV) and clinical target volume (CTV) are oncological volume concepts that must be treated to a certain dose in order to achieve the aim of radiotherapy (ICRU 50 1993; ICRU 62 1999). GTV and CTV are not dependent on the radiotherapy technique or on treatment planning. e actual delineation depends on the imaging technique used, the time of delineation, and the experience and judgment of the radiation oncologist. GTV and CTV are used in brachytherapy (BT) in the same way as in external beam radiotherapy (EBRT), since these volumes are general oncological concepts applicable for any radiotherapy technique. Organ movements and inaccuracies in beam setup and patient setup are potential sources of uncertainties during EBRT. It is possible to compensate for these uncertainties during dose planning by using a planning target volume (PTV), which is constructed by adding a margin to the CTV. e PTV concept was ocially established and recommended in ICRU reports (ICRU 50 1993; ICRU 62 1999; ICRU 71 2004; ICRU 78 2007; ICRU 83 2010). e concept has been successfully and widely used within EBRT. During dose planning, it is aimed to cover the PTV with the prescription dose. e consequence of margin application is that the prescription dose plateau is increased in size. erefore, the risk is reduced that geometric uncertainties will lead to under-dosage of the
CTV during fractionated EBRT. In general, this is not linked to a dose escalation, but only to an increase in the treated volume.
