3. Definition of Volumes

Abstract

Stereotactic radiotherapy delivers a very high dose to the target while relying heavily on tight margins and steep dose gradients to reduce the impact on organs at risk. Stereotactic radiosurgery has historically been used as a neurosurgery technique but in this context volumes have not strictly been defined. As introduced in ICRU Reports 50, 62, 71, 78, and 83 several volumes related to both tumor and normal tissues have been defined for use in the treatment planning and reporting processes (ICRU, 1993; 1999; 2004; 2007; 2010). It has been practice in (e.g., cranial radiosurgery) not to prescribe and, instead, to deliver spherical dose distributions. However, delineation of these volumes is a mandatory step in the planning process, as dose cannot be prescribed, recorded, and reported without specification of target volume and normal tissue at risk volume. In order to compare and reproduce clinical results, it is important that the definitions of the target and the organs at risk be as clear and as reproducible as possible. The volumes to be considered are: