This ontology describes commonly contoured (anatomical and treatment planning) structures for radiation treatment planning. 22000 structures labels (created over a 16 years period in our radiation department) were extracted, classified and categorized to produce this ontology. Lymph nodes delineation international guidelines are provided. This ontology was created to ease and standardize the integration of radiation oncology data into clinical datawarehouses for multicentric studies. The high granularity of this ontology will allow precise dosimetric evaluations.