IMAGING OF NASOPHARYNGEAL CARCINOMA WITH TC-99M MIBI

Purpose: Differentiation of recurrent nasopharyngeal carcinoma (NPC) f rom radiation fibrosis using conventional diagnostic methods can be di fficult. The authors prospectively studied patients with NPC to determ ine the efficacy of Tc-99m MIBI scintigraphy in detecting the primary, residual, and recurrent tumors.Materials and Methods: The authors per formed Tc-99m MIBI SPECT studies of the head and neck and whole-body s cans on 21 healthy adult volunteers and 43 patients with NPC before (n = 26) or after (n = 17) radiotherapy. The images were qualitatively a ssessed by comparing the nasopharyngeal uptake to scalp radioactivity. MIBI uptake index was calculated as a ratio of mean counts per pixel in the normal nasopharynx or tumor to mean counts per pixel in the sca lp. Results: There was significantly higher uptake of Tc-99m MIBI by N PC than normal nasopharynx and radiation fibrosis (P <.05). The author s determined the optimum cutoff MIBI uptake index value of 1.3 with a sensitivity of 97%, a specificity of 100%, a positive predictive value of 100%, a negative predictive value of 96%, and an accuracy of 98% f or diagnosing NPC. Conclusion: This study suggests that Tc-99m MIBI SP ECT is useful for detecting primary NPC and for differentiating residu al or recurrent tumor from radiation fibrosis. The authors propose the cutoff MIBI uptake index value of 1.3 for diagnosing NPC.