Cross-sectional nodal atlas: A tool for the definition of clinical target volumes in three-dimensional radiation therapy planning

When radiation is used with curative intent, the radiation volume usually e ncompasses the detectable tumor and the anatomic areas thought to be at ris k for metastatic spread. The International Commission on Radiation Units an d Measurements Report No. 50 (1) defines gross tumor volume (GTV) as the gr oss palpable or visible or demonstrable extent and location of the malignan t growth. The same report defines clinical target volume (CTV) as a volume that contains a demonstrable GTV and or is considered to contain (only) mic roscopic, subclinical extensions at a certain probability level. In clinica l practice, the determination of the extent of the CTV is based on the know ledge of the patterns of spread for each specific disease presentation. Add itional reliable information can be obtained from patterns-of-failure analy sis and necropsy series. For most tumors, the CTV will encompass one or mor e nodal stations, usually near the primary lesion. Traditionally, the locat ion and boundaries of these nodal stations have been established in referen ce to anatomic landmarks during the standard simulation setup. Therefore, t he radiation oncologist has been specifically trained to determine the boun daries of the different nodal stations on standard two-dimensional radiogra phs, especially in the anteroposterior and posteroanterior views. With the advent of three-dimensional (3D) virtual clinical target definition, the ra diation oncologist faces the challenge of defining the CTV on cross-section al CT or magnetic resonance images. Unfamiliarity with this new technique c an make correlations with the known spatial references difficult to establi sh. The present nodal atlas is intended to assist radiation oncologists who will use new 3D virtual clinical target definition and treatment planning programs.