Objective To study the early evaluation value of ¹⁸F-FDG PET/CT imaging in nasopharyngeal carcinoma on the 7-day after different models of radiotherapy, including conformal radiotherapy(CRT) and intensity-modulated radiotherapy(IMRT).

Methods PET/CT imaging was performed in 21 cases of CRT group and 19 cases of IMRT group on the 7-day after radiotherapy. The visual examination was performed and the maximum standardized uptake value(SUVmax) was measured, and the results were compared with the two years clinical follow-up and the result of pathological biopsy.

Results Two years clinical follow-up of the CRT group confirmed there was no residual tumor. There was no residual tumor in 17 cases and 2 cases were positive of the IMRT group confirmed by biopsy. The SUV_max of the CRT group and the IMRT group were 9.57±4.33 and 9.40±3.32 respectively before radiotherapy without significant difference(t=-0.43, P=0.132). SUV_max of the CRT group and the negative patients confirmed by biopsy of the IMRT group were 2.38±0.34 and 3.1±0.55 respectively after radiotherapy with significant difference (t=-3.4, P=0.002). The accuracy rate and the false positive rate of visual examination of the CRT group were 76.2% and 23.8% respectively. The accuracy rate and the false positive rate of visual examination of the IMRT group were 63.2% and 36.8% respectively.

Conclusion s One week after nasopharyngeal carcinoma CRT is the feasible time-point for ¹⁸F-FDG PET/CT assessment. SUV_max of the IMRT group on 7-day after radiotherapy was higher than that in CRT group, so this time-point is not the best evaluation time-point of the PET/CT.