DISEASE CHARACTERISTICS: Radiologically confirmed persistent or metastatic follicular or papillary thyroid cancer following total thyroidectomy and radioiodine ablation therapy Metastatic disease confirmed histologically or cytologically or by elevated thyroglobulin levels No radioiodine uptake by whole body scanning Stable iodine contamination from radiologic contrast material within the past 10 months allowed, if absence of current contamination demonstrated by less than 80 micrograms of iodine in a 24 hour urine collection