For low risk patients who have had thyroidectomy and remnant ablation, I-131 scanning may not be necessary at all, but most still do it. A one-time thyrogen stimulated throglobulin level 9-12 months after initial treatment may be all that is needed (assuming a negative result -- <1-2). Then good ultrasound follow-up and suppressed Tg levels. IF higher risk or Tg-Antibody positive, then the I-131 WBS may be more regular/useful part of follow-up. In general, the combination of Tg levels and good ultrasound will pick up most recurrent/persistent cancer.
I am interested in what answer you receive!!