Fig. 2

Schematic sagittal overview of used method. a The nearby rectal wall (green) was defined as that part of the rectal wall (red) that lies within a 1 mm expansion (dashed blue) around the tumor (blue). b For both tumor and nearby rectal wall, distances between the reference (solid lines) and daily (dotted lines) delineations were determined. For all points of the nearby rectal wall the corresponding i.e. nearest, tumor point was determined. As an example, displacements for a pair of corresponding points of the position surrogate and tumor are shown by the arrows. As measure of how well position surrogate and tumor mobility are in agreement, Pearson’s correlation was determined between displacements of each pair of corresponding points, i.e. the correlation between the green and blue arrow, for all points of the nearby rectal wall