194P Motion of lymph nodes and the effect on the dose coverage in proton therapy of lung cancer

Proton therapy is sensitive to density changes, which occur in patients with large tumor motion. Individual margins, or internal target volumes (ITV) account for motion, are used the primary (GTVp), while nodes (GTVn) treated a fixed margin. The aim of this study was evaluate effect nodal motion on dose coverage proton therapy. included 58 lung cancer at least an involved upper mediastinal lymph node (4), infracarinal (7), and/or hilar (10). All had 4DCT. total GTVn delineated planning phase and expanded 5 mm clinical volume (CTVn). treatment plan robustly optimized ensure (V95%) 95%. divided into separate structures GTVn4, GTVn7 GTVn10 propagated other phases For each GTVn, amplitude determined using center mass method. To planned dose, evaluated all station, V95% their respective CTV compared 3D 4D evaluation doses. highest superior-inferior direction (table). largest average amplitudes were 1.9 (left-right), 1.7 (anterior-posterior) 5.7 (superior-inferior). 3D-evaluation >95% but ranged from 88–93% individual stations. Loss due breathing (4D-3D) most 1.8% (CTVn7). stations 93% (10L 10R), remained >92% evaluation. minimal. Although higher nodes, adequate.