RESUMEN
<p><b>OBJECTIVE</b>The primary aim of this prospective study was to use serial (18)F-FDG PET-CT imaging to evaluate the trend of the tumor's maximum standardized uptake value (SUVmax) during radiotherapy (RT) for patients with nasopharyngeal carcinoma (NPC), and to explore the possibility of early evaluation of the tumor bio-metabolic response during radiotherapy.</p><p><b>METHODS</b>Sixty patients with biopsy-proven primary NPC were prospectively enrolled into the study. All patients underwent four (18)F-FDG PET-CT scans: one initial scan before RT/cisplatin based concurrent chemoradiotherapy, at the point of 50 Gy during RT, the end of RT, and one month after RT, respectively. Tumor (18)F-FDG uptake was analyzed according to the World Health Organization pathological type.</p><p><b>RESULTS</b>There was a significant difference (P < 0.001) of the mean of SUVmax of the primary site among pretreatment (11.20 ± 5.37) and posttreatment at the dose of 50 Gy (3.50 ± 1.59), at the end of RT (3.05 ± 1.56) and one month after RT (2.52 ± 1.46). There was also a significant difference (P < 0.001) of the mean of SUVmax of neck node site. However, there was a significant difference of the SUVmax between histological WHO type IIb and type IIa in the primary site (P = 0.046) [(67 ± 19)% reduction at dose 50 Gy for type IIb vs. (55 ± 24)% for type IIa] but not in the lymph nodes.</p><p><b>CONCLUSIONS</b>Early PET scan during or right after RT instead of conventional 3 months interval after RT is indicated to evaluate the tumor response and to develop individualized adaptive radiotherapy in NPC. Our next study will attempt to demonstrate the results based on long-term follow-up data.</p>