<prompt> Which of the following is used in the treatment of well differentiated thyroid carcinoma:I-131Technetium ScanPhosphateMIBG  <response>: Ans. a I131Ref: Schwartz 10th edition, Page 1543 I131 is used in the treatment of metastatic well differentiated cancers. I123, Tc 99m are all used only for diagnostic purposes. 