Combination treatment (CXRPT) of external beam radiation (XRT) plus radioactive iodine (RAI)

The goal of this study is to evaluate combined radioactive iodine (RAI, 131-I) and external beam radiotherapy (XRT) to optimize the radiation dose delivered to treat well differentiated thyroid cancers (DTC) with iodine-avid metastases. The investigators hypothesize that precise dosimetric planning will permit this combined RAI-XRT radiotherapeutic approach to be safe and permit higher tumor radiation doses than could otherwise be delivered. Patients with metastatic well-differentiated DTC) that is not completely resectable with macroscopic invasion of tumor into cervical soft tissues and/or non-resectable distant metastases, are the target study population. The primary objective is to evaluate safety as defined by the incidence of maximum grade 3 or greater NCI CTCAE toxicity observed during the treatment period and for the first 30 days following completion of radiotherapy. Secondary endpoints will evaluate efficacy at 6 months and feasibility of this combination to deliver a minimum cumulative dose of 80 Gy to the index tumors selected prior to treatment initiation. The investigators plan to enroll 48 subjects at an accrual rate of 1 subject per month over a study duration of 4 years.