Abstract
PURPOSE: The study compared interobserver variation in the delineation of the primary tumour (GTVp) and lymph nodes (GTVln) between three different 4DCT reconstruction types; Maximum Intensity Projection (MIP), Mid-Ventilation (Mid-V) and Mid-Position (Mid-P). MATERIAL AND METHODS: Seven radiation oncologists delineated the GTVp and GTVln on the MIP, Mid-V and Mid-P 4DCT image reconstructions of 10 lung cancer patients. The volumes, the mean standard deviation (SD) and distribution of SD (SD/area) over the median surface contour were compared for different tumour regions. RESULTS: The overall mean delineated volume on the MIP was significantly larger (p<0.001) than the Mid-V and Mid-P. For the GTVp the Mid-P had the lowest interobserver variation (SD=0.261cm), followed by Mid-V (SD=0.314cm) and MIP (SD=0.330cm) For GTVln the Mid-V had the lowest interobserver variation (SD=0.425cm) followed by the MIP (SD=0.477cm) and Mid-P (SD=0.543cm). The SD/area distribution showed a statistically significant difference between the MIP versus Mid-P and Mid-P versus Mid-V for both GTVp and GTVln (p<0.001), with outliers indicating interpretation differences for GTVp located close to the mediastinum and GTVln. CONCLUSION: The Mid-P reduced the interobserver variation for the GTVp. Delineation protocols must be improved to benefit from the improved image quality of Mid-P for the GTVln.
