Figure 1.

The orthogonal distance between planning target volume (PTV) and esophagus measured by examining each slice containing PTV and finding the closest orthogonal with either the shortest orthogonal distance between the edge of the PTV and the edge of the esophagus if esophagus and PTV remain separate or the maximum distance between the PTV and esophagus edges if these 2 structures overlap. The change in distance was found by subtracting the orthogonal distance on the planning scan from the distance on the cone beam computed tomography (CBCT) plan. Therefore, a negative change in distance corresponds to a change where the distance between esophagus and PTV decrease or the amount of overlap increases in the case of overlap.