Inclusion Criteria:

- Pathologically confirmed differentiated thyroid cancer

- Patient with locally advanced tumor (T4a, tumor of any size extending beyond the
thyroid capsule to invade subcutaneous soft tissues, larynx, trachea, esophagus, or
recurrent laryngeal nerve or T4b, tumor invades prevertebral fascia or encases
carotid artery or mediastinal vessels or N1b, unilateral, bilateral, or contralateral
cervical or mediastinal lymph node positive), or locoregionally recurrent tumor

- All patients must have radiographically assessable disease

- No previous irradiation to the planned field

- Age of ≥ 18 years

- Performance status of 0 to 2 on the Eastern Cooperative Oncology Group (ECOG) score

- Required Entry Laboratory Parameters WBC count ≥ 1,000/mm3; hemoglobin level ≥ 7.5
g/dL; platelet count ≥ 100,000/mm3; creatinine ≤ 3.0 mg/dL

- Oral intake (including J-tube feeding) of ≥ 1,500 calories/day should be maintained.

- Signed informed consent form prior to study entry

Exclusion Criteria:

- Patient with anaplastic carcinoma (focal anaplastic change associate with
differentiated thyroid cancer is not excluded)

- Age of <18 years

- Previous history of RT adjacent to planned field

- Poor performance status of 3 to 4 on the Eastern Cooperative Oncology Group (ECOG)
score

- Pregnant or breast feeding status

- Previous history of uncontrolled other malignancies within 2 years