ABSTRACT
Key points 204 Bibliography 204 Further reading 206
Volume specifications in radiotherapy (Fig. 14.1) are described in publications 50 and 62 of the International Commission on Radiation Units and Measurements (ICRU, 1999). Even the smallest volume, the gross tumour volume (GTV), contains normal tissue elements (e.g. blood vessels and normal connective tissue) within the tumour. In addition, the clinical target volume (CTV) encompasses a relevant number of normal parenchymal cells of the respective organ, intermingled between the suspected tumour cells. The volume difference between the CTV and the treated volume (TV) – the volume enclosed by a surface of the clinically effective isodose – is exclusively composed of normal tissue. In all these normal cells and structures, radiation side-effects may be induced. However, all the normal tissues within the TV are unavoidably exposed to the entire tumour dose, which therefore may be limited by the normal tissue volume, depending on the size of the TV.
