Residual setup errors and dose variations with less-than-daily image guided patient setup in external beam radiotherapy for esophageal cancer

Substantial residual setup errors would occur for treatment fractions without IG even if the most frequent less-than-daily IG strategy was to be used, which could lead to significant daily dose variations for the target volume and adjacent normal tissues. Daily image guidance is recommended throughout the course of treatment in conformal radiotherapy for esophageal cancer.