F-18 FLUOROMISONIDAZOLE TUMOR TO MUSCLE RETENTION RATIO FOR THE DETECTION OF HYPOXIA IN NASOPHARYNGEAL CARCINOMA

In vivo demonstration of hypoxia is of significance for tumour patient management. Fluorine-18 fluoromisonidazole ([F-18]FMISO) is a proven hypoxic imaging agent, We developed an [F-18]FMISO tumour to muscle re tention ratio (TMRR) for the detection of tumour hypoxia in nasopharyn geal carcinoma (NPC). Data were acquired by positron emission tomograp hy (PET) of the nasopharynx and neck after intravenous injection of 37 0 MBq of [F-18]FMISO, Two imaging protocols were adopted: a long proto col for comprehensive dynamic information and a short protocol for a s imple, clinically convenient imaging procedure, Tomograms were reconst ructed and evaluated visually. ROI analysis on the basis of time-activ ity curve evaluation was performed to calculate the TMRR of NPC or cer vical nodal metastases (CNMs) in relation to the suboccipital muscles at 2 h. The calculation of the TMRR was exactly the same for both the long and the short protocol as two 30-min composite frames had been cr eated immediately after intravenous injection and 2 h after injection of [F-18]FMISO in the long protocol. The normal tissue to muscle reten tion ratio (NTMRR) was derived similarly from the normal nasopharynx. The data of 12 controls and 24 patients with NPC were analysed. The lo ng protocol was used in 15 patients, and the short protocol in nine, I n controls, the mean NTMRR+/-1 SD was 0.96+/-0.14. The mean TMRRs for NPC and CNMs were 2.56+/-1.50 and 1.35+/-0.51, respectively; these val ues were significantly higher than the mean NTMRR for normal controls (P<0.005 in each case). At the retention threshold value of 1.24, tumo ur hypoxia occurred in 100% of the primary lesions of NPC and 58% of C NMs, The TMRR for undifferentiated carcinoma was significantly lower t han that for non-keratinized carcinoma (P<0.05), The [F-18]FMISO TMRR is a simple and clinically useful index for detecting tumour hypoxia i n NPC.