Fig. 1

Reference outlinings of GTV, CTV, and PTV are shown on (a) a CT image; and (b) an MR image. Outlining of (c) GTV, (d) CTV, and (e) PTV for the 41 participating institutions. Abbreviations: GTV, gross tumor volume; CTV, clinical target volume; PTV, planning target volume; CT, computed tomography; MR, magnetic resonance