Clinical target volume. Principles and limits

The clinical target volume (CTV) is regarded fundamental for radiotherapy planning by the International Commission on Radiation Units and Measurements (ICRU). The aim of this article is to give an overview on the basics and problems of defining the CTV for radiotherapy planning. After briefly defining CTV, a short description of the process to homogenize CTV in intraindividual comparisons is given, where special attention is paid to radiological requirements. This information is summarized in a number of tables. CTV is the most complex volume among the target volumes that have been defined by the ICRU. A survey of the determinants of the definition of CTV is given. This overview on the basic rules of how to define CTVs can help to increase the understanding of the radiological requirements for optimum imaging to support radiotherapy planning regardless of the specialty of the physician. (orig.)