Impact of coronal and sagittal views on lung gross tumor volume delineation

To study the impact of coronal and sagittal views (CSV) on the gross tumor volume (GTV) delineation on CT and matched PET/CT scans in non-small cell lung cancer.

GTV delineations were performed by 11 experienced radiation oncologists on CT and PET/CT in 22 patients. Two tumor groups were defined: Group I: Primary tumors surrounded by lung or visceral pleura, without venous invasion, and without large extensions to the chest wall or the mediastinum. Group II: Tumors invading the hilar region, heart, large vessels, pericardium, and the mediastinum and/or associated with atelectasis. Tumor volumes and inter-observers variations (SD) were calculated and compared according to the use of axial view only (AW), axial/coronal/sagittal views (ACSW) and ACSW/PET (ACSWP).

CSV were not frequently used (57.4% out of 242 delineations on CT). For group I, ACSW didn't improve significantly mean GTVs. SDs were small on CT and on PET (SD=0.3cm). For group II, ACSW had 27-46% smaller observer variation (mean SD=0.7cm) than AW (mean SD=1.1cm). The smaller observer variation of ACSW users was associated with, on average, a 40% smaller delineated volume (p=0.038). Mean GTV of ACSWP was 21% larger than mean GTV of ACSW on CT.

For smaller lung tumors surrounded by healthy lung tissue the effect of multiple axis delineation is limited. However, application of coronal and sagittal windows is highly beneficial for delineation of more complex tumors, with atelectasis and/or pathological lymph nodes even if PET is used.