ABSTRACT
The target volume in curative radiotherapy must unavoidably include a substantial amount of normal tissue, despite optimum conformation of the treatment fields to the tumour and precise treatment planning and application, for several reasons: First, malignant tumours infiltrate microscopically into normal structures, which need to be included in the high-dose volume as a tumour margin. Second, normal tissues within the tumour, e.g. soft tissue and blood vessels, are exposed to the full tumour dose. Third, normal structures in the entrance and exit channels of the radiation beam may also be exposed to clinically relevant doses. Therefore, effective curative radiotherapy is inevitably associated with an accepted risk for (severe) early and late radiation side effects (‘adverse events’) in order to achieve adequate tumour cure rates. The optimum radiation dose in curative radiotherapy is defined as the dose, which is associated with a certain, low – usually ≤5% – incidence of sequelae of a defined severity in cured patients (‘complication-free healing’). The clinical manifestation of side effects therefore must be considered an indicator for optimum treatment and maximum tumour cure probability; side effects cannot a priori be considered as a consequence of incorrect treatment.
