ABSTRACT
Volume specifications in radiotherapy are defined in reports 50 and 62 of the International Commission on Radiation Units and Measurements (ICRU) (6,7). In 2013, ICRU Report 89 also focused on volume concepts in image-guided, adaptive radiotherapy including brachytherapy, mainly based on studies in cervix cancer (8). Even the smallest tumour volume defined, that is, the gross tumour volume, contains normal tissue elements, for example blood vessels and connective tissue components. In addition, the clinical target volume (CTV) also encompasses a relevant number of normal parenchymal cells of the respective organ, with the suspected tumour cells intermingled. Moreover, the volume difference between the CTV and the treated volume (TV), that is, the volume enclosed by a surface of a clinically effective isodose, is exclusively composed of normal tissue components. In all these normal cells and structures within the high-dose volume, radiation effects and hence adverse events of therapy may be induced. However, all the normal tissues within the TV are unavoidably exposed to the complete radiation dose applied to the tumour; the clinical consequences of this normal tissue exposure therefore may limit the TV dose, depending on the size of the TV.
