The accuracy of target delineation in laryngeal and hypopharyngeal cancer

Background and purpose. To determine the spatial correspondence between the gross tumor volume (GTV) delineated on computer tomography (CT) and the actual tumor on histopathology.Material and methods. Sixteen patients with T3 or T4 laryngeal or hypopharyngeal cancer underwent a CT scan before total laryngectomy. The GTV was delineated on CT by three independent observers and by consensus between the three observers. After surgery, whole-mount hematoxylin-eosin stained (H&E) sections were obtained. One pathologist delineated the tumor in the H&E sections (tumor<inf>H&E</inf>). The reconstructed specimen was registered to the CT scan in order to compare the GTV to the tumor<inf>H&E</inf> in three dimensions. The overlap between the GTV and the tumor<inf>H&E</inf> was calculated and the distance between the volumes was determined.Results. Tumor tissue was delineated in 203 of 516 H&E sections. For 14 patients a detailed analysis could be performed. The GTV volume was on average 1.7 times larger than the volume of the tumor<inf>H&E</inf>. The mean coverage of the tumor<inf>H&E</inf> by the consensus GTV was 88%. tumor<inf>H&E</inf> tissue was found at 1.6 mm to 12.9 mm distance outside the GTV depending on observer and patient.Conclusions. GTVs delineated on CT for laryngeal and hypopharyngeal cancer were 1.7 times larger than the tumor. Complete coverage of the tumor by the GTV was, however, not obtained.