<prompt> Which of the following is used in the treatment of well differentiated thyroid cancer?32 P131 I99mTc131I-MIBG  <response>: I 131 is used in the treatment of well differentiated thyroid cancer and hypehyroidism. I 131 has a half life of 8 days and emits beta paicles as well as gamma rays. Radiation dose to thyroid is mainly due to the emitted beta paicles 90 rather than gamma radiation. Ref: Oncology for Health-Care Professionals By V. Pervan, Page 262; Radiation in Medicine: A Need for Regulatory Reform By U.S. Nuclear Regulatory Commission, Page 74 