Figure 6: Scenario A: in a simple shape-like sphere or cylinder, the axial image would seem like a circle. In such tumors when there is a centripetal shrinkage due to the simple geometry application of change in unidimensional imaging would reflect the change in area on the axial slice and also the change in volume when the whole three-dimensional structure is taken into account. Scenario B: again in this situation the shape is simple; however, the tumor underwent a centrifugal shrinkage mainly in one dimension. The change in area on the axial slice or the change in volume (when the whole structure is accounted for) is not proportionately depicted to be change in unidimensional dimension in accordance with RECIST. However, a change is still depicted. Scenario C: in complex irregular shapes, as seen in the images, due to use of longest dimension for comparison in prechemotherapy and postchemotherapy scan even though, there has been a decrement in the area of the tumor on axial slice (which would in turn reflect a decrement in volume); this change has not been picked up by presently used radiological response criteria. As seen in Figure 5 head and neck cancers do not uncommonly have such shapes.