The Role of Postoperative External Beam Radiotherapy in Differentiated Thyroid Cancer with Focal Anaplastic Change

and nodal control at 1-, 2-, and 4-year were 70.6%, 68.7%, and 65.6%; 75.3%, 71.2%, and 67.0%; 83.3%, 83.3%, and 83.3%; 91.6%, 91.6%, and 91.6%, respectively. Among 25 patients with post-treatment measurable SUVmax in the primary tumor sites, 7/11 patients with SUVmax .6.0 had persistent disease, compared to 2/14 with SUVmax\= 6.0 (4.8 and 5.6) (p\0.05); 6/9 of patients with persistent primary disease had SUVmax reduction \60%. Seventeen patients had residual enhancement in the primary site, 6/7 patients (85.7%) with tumor size reduction \40% had persistent or progressive disease, compared with 3/10 patients (30%) reduction .40% (p \ 0.05). Among 24 patients with post-treatment PET/CT measurable residual LNs, 3 relapsed in the regional had nodal size reduction \40%, compared to 0/21 failure if nodal size reduction .40% (p \ 0.001). There was no significant difference of post-treatment SUVmax reduction in regional failure. No patients developed local or regional recurrence 3 months or more after completion of definitive RT or CRT. All late disease relapses were distant metastases. Conclusions: High-resolution dedicated head and neck FDG 18 -PET/CT CECT is helpful in accurate tumor target delineations. Post-treatment residual disease and corresponding SUVmax reductions predicted disease local and regional control. Distant metastases are still the challenge affecting long-term disease free survival.