Image-guided radiation therapy using surgical clips for localization of colonic metastasis from thyroid cancer.

A 67-year old man with a history of papillary thyroid cancer (PTC) presented with metastatic disease to the left colon in the form of a 6.1x1.0 cm bleeding, ulcerated mass. Radiopaque surgical clips were used as fiducial markers to localize the gross tumor volume (GTV) as well as the corresponding clinical target volume (CTV) and planning target volume (PTV). Daily cone beam computed tomography (CBCT) image guidance was utilized to verify the tumor position. Inter- and intrafraction movement of the tumor mass was assessed. Gastrointestinal bleeding was controlled using palliative image-guided radiation therapy (IGRT).