Inclusion Criteria

Inclusion Criteria common for all study subjects prior to randomisation:

- Histologically confirmed new diagnosis of DTC (including Hürthle-cell carcinoma)

- Age 18-80 years

- Performance Status of 0-2

- Tumor stage T1b to T4 with the possibility of lymph node involvement and distant
metastasis according to the [TNM] staging system

- One- or two stage thyroidectomy, with or without central lymph node dissection

- Patient´s written informed consent

- Ability to comply with the protocol procedures

Exclusion criteria for all study subjects prior to randomisation:

- Anaplastic or medullary carcinoma

- History of prior malignancy within the past 5 years with limited life-time
expectancy, except for cured non-melanoma skin cancer, cured in situ cervical
carcinoma, or other treated malignancies with no evidence of disease for at least
three years.

- Positive pregnancy test or breast feeding

- Any other severe acute or chronic medical or psychiatric condition, or laboratory
abnormality that would impart, in the judgment of the investigator, excess risk
associated with study participation, or which, in the judgment of the investigator,
would make the patient inappropriate for entry into this study.

- Recent iodine contamination

After Randomisation

I-124 arm:

A: Inclusion criteria for no remnant ablation (low risk DTC):

- Stage I (according to AJCC, ref. 1,33) papillary or follicular carcinoma with the
possibility of lymph node involvement but no distant metastasis and no microscopical
residual disease (Patient age <45y: any T, any N, M0; Patient age 45y or older: T1,
N0, M0)

- I-124 uptake only in thyroid bed

- Absence of aggressive malignant histologic subtypes, including tall-cell, insular,
poorly differentiated and diffuse sclerosing thyroid cancer

B: Inclusion criteria for remnant ablation (high risk DTC):

- All other [TNM] stages (stage II to stage IV C)

- Presence of aggressive malignant histologic subtypes, including tall-cell, insular,
poorly differentiated and diffuse sclerosing thyroid cancer

- I-124 uptake in and outside thyroid bed

Standard arm:

-Standard I-131 ablation concept as defined for all T1b to T4 subjects.