Introduction

In vivo demonstration of hypoxia is of significance for cancer patient management. [F-18]-FMISO is a proven hypoxic imaging agent. This study assessed [F-18]-FMISO tumor:muscle retention ratio (TMRR) in detecting tumor hypoxia in nasopharyngeal carcinoma (NPC).

Materials and Methods

Data were acquired by dynamic PET after IV injection of 370 MBq of [F-18]-FMISO for 120 min. Tomograms were reconstructed and evaluated visually. ROI analysis was performed to calculate tumor:muscle retention ratio of NPC or cervical nodal metastasis (CNM) to the suboccipital muscles at 2 hr. Normal tissue:muscle retention ratio (NTMRR) was derived similarly from the normal nasopharynx.

Results

TMRRs were determined in 12 proven pts with NPC with 21 cervical nodal metastases, and NTMRRs in 12 normal controls (N). In N, the mean NTMRR ± 1 s.d. was 0.96 ± 0.14. The mean TMRR for NPC and CNM were 3.65 ± 2.98 and 1.23 ± 0.27, respectively, and were significantly greater than N (p < 0.005 vs. NPC and p < 0.005 vs. CNM). At the threshold value of 2 s.d. above the mean NTMRR, tumor hypoxia occurred in 100% (12/12) of the primary lesion and 48% (10/21) of CNM. All hypoxic lesions had obvious [F-18]-FMISO retention at 2 hr visually.

Conclusion

Our initial studies indicate that TMRR is a useful parameter easily obtained for detecting tumor hypoxia, and that nasopharyngeal carcinoma has a high occurrance rate of hypoxia, especially the primary lesion.

Figure 1. Display of FMISO imaging, time-activity curves and retention ratios in a control (top) versus a patient with primary NPC (middle) and lymph node metastases (bottom).

Figure 2. PET images of FMISO uptake and TMRR in a patient with NPC before and 6 months after a course of fractionated radiation therapy, to which there was a complete response.