Image-guided radiotherapy using surgical clips as fiducial markers after prostatectomy: A report of total setup error, required PTV expansion, and dosimetric implications

In the absence of IGRT, a non-uniform PTV margin of 6 mm LR, 8 mm AP, and 9 mm SI should be considered. Use of clips as fiducial markers can decrease the total setup error, enable a smaller PTV margin, and improve rectal sparing.