99Tcm-MIBI SPECT in detection of primary nasopharyngeal carcinoma and in differentiation of residual or recurrent lesions after radiotherapy

Objective: To investigate the diagnostic potential of 99Tcm-methoxyisobutylisonitrile (MIBI) SPECT in evaluating the extent of primary disease and differentiating residual/recurrent lesions post radiotherapy in patients with nasopharyngeal carcinoma (NPC). Methods: Twenty patients with primary NPC histologically confirmed with biopsy underwent repeated 99Tcm-MIBI SPECT before radiotherapy and at 3 months, 6 months after radiotherapy. The scintigraphic findings were compared with that of CT/MRI. Nasopharyngeal-to-scalp ratios were obtained as MIBI uptake index (MUI). The recurrent lesions were judged with biopsy and (or) clinical follow-up which lasted for 18 months after radiotherapy. Receiver operating characteristic analysis was used to defined the cut-off of MUI. Results: When MUI 2.15 was used as cut-off, the sensitivity, specificity and accuracy for detecting the primary NPC were all 95%. The optimum cut-off of 1.32 of MUI was defined with sensitivity of 3/4, specificity of 93.8%, and accuracy of 90.0% for differentiating residual/recurrent lesions from the benign process post radiotherapy, while CTPMRI evaluations showed sensitivity of 3/4, specificity of 81.3%, and accuracy of 80.0%. A combination of CT/MRI and 99Tcm-MIBI SPECT for 16 NPC patients with congruent results showed sensitivity of 2/2, specificity of 92.9%, and accuracy of 93.8% for differentiating residual/recurrent NPC from benign lesions. Conclusions: 99Tcm-MIBI SPECT may play a role in detecting primary NPC. The combination of CT/MRI and 99Tcm-MIBI SPECT may give more accurate diagnosis and differentiation in distinguishing residual/recurrent lesions in the post radiotherapy follow-up. (authors)