*4.4. Follow-Up and Outcome*

Outcome of RAI therapy was assessed six to nine months after initial therapy. The follow up was based on physical examination, neck ultrasound, determination of the level of stimulated thyroglobulin (Tg)-level by two assays (Roche Elecsys® Tg II, Roche Diagnostics GmbH, Mannheim, Germany) with a measuring range of the Roche assay as 0.04–500 ng/mL with a theoretical lower limit of detection of 0.04 ng/mL and a theoretical lower limit of quantitation of 0.1 ng/mL with an error of < 30% or Siemens Immulite with an analytical sensitivity of 0.2 ng/mL and a functional sensitivity of 0.5 ng/mL), and Tg-recovery (Roche Elecsys® Tg II Confirmatory Test) as well as a diagnostic I-131 whole body scintigraphy (WBS), which was performed approximately 72 h after application of 370 MBq I-131 (10 mCi) in hypothyroidism or after administration of rhTSH i.m. on two consecutive days. In case of any pathological finding in the WBS, an additional single-photon-emission computed-tomography (SPECT)/low dose computer-tomography (CT) of the relevant region was performed (most often neck and thorax). Three days after stimulation, Tg and Tg recovery were determined.

Patients were classified as responders to adjuvant radioiodine therapy if stimulated Tg-levels were lower than 0.5 ng/ml, the thyroid bed was empty or showed a hyperechoic region, and no suspicious lymph nodes were found in the neck ultrasound and if the uptake in the thyroid bed was rated as non-relevant and no pathological uptake was seen outside the thyroid bed according to the WBS. In addition, if a second radioiodine treatment was needed for any given reason, the adjuvant radioiodine therapy was considered as inadequate.
