The primary objective of this study is to estimate the 5 year locoregional control rate after External Beam Radiotherapy (EBRT) in the patient with locally advanced differentiated thyroid cancer. In a prior retrospective trial for this same group of patients, the 5 year locoregional control rate was 85% in EBRT group and 70% in no EBRT group. For the total number of patients to detect a minimum of 20% improvement in 5 year locoregional control rate with 80% of statistical power and the 5% significance level, the table for sample size planning given by Makuch and Simon was chosen. Forty-three patients are required for this regimen to regard as worthy of further investigation. Considering 15% follow up loss, 50 eligible patients will be enrolled.

The standard approaches to the treatment of differentiated thyroid cancer include surgical resection, radioactive iodine treatment, and thyroid-stimulating hormone suppression. The role of external beam radiotherapy (EBRT), however, remains controversial.

The purpose of this phase II study is to evaluate the impact of EBRT on the locoregional control in locoregionally advanced or recurrent differentiated thyroid cancer patients.

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