FIGURE 1. A 45-y-old man with invasive squamous cell carcinoma of left palatine tonsil. (A) Patient underwent ¹⁸F-FDG PET scan simultaneously with CT before initiation of therapy. Axial PET (middle) image reveals intense ¹⁸F-FDG uptake in left tonsil (vertical arrow) as well as in a left jugular lymph node (horizontal arrow), consistent with primary disease and local lymph node metastasis, respectively (locally advanced disease). Axial CT (left) and PET/CT fusion (right) images confirm these findings (arrows). Comprehensive examination was obtained by simultaneous CT and PET/CT, combining anatomic data with functional or metabolic information. (B) Same patient underwent ¹⁸F-FDG PET scan simultaneously with CT 1 mo after completion of neoadjuvant chemoradiotherapy. Axial PET (middle) and PET/CT (right) images demonstrate interval resolution of primary disease in left tonsil and metastatic disease in a left jugular lymph node, consistent with complete response to therapy. This patient subsequently underwent surgical resection and has been disease-free during follow-up period of 6 mo. Although further follow-up is necessary, ¹⁸F-FDG PET was valuable in determination of complete response to therapy. PET/CT studies were obtained on a GE Discovery LS unit—a PET/CT fusion system combining GE LightSpeed multislice CT and Advance NXi PET (GE Medical Systems).