Diagnosis of recurrent brain tumor: Value of ²⁰¹TI SPECT vs ¹⁸F- fluorodeoxyglucose PET

OBJECTIVE. This prospective study was designed to compare the sensitivity and specificity of a relatively simple examination, ²⁰¹TI chloride single- photon emission CT (SPECT), with a more complex examination, ¹⁸F- fluorodeoxyglucose (FDG) positron emission tomography (PET), in patients thought to have recurrent brain tumor. Because both agents have been shown to be markers of viable tumor, we hypothesized that their sensitivity and specificity should be the same. SUBJECTS AND METHODS. Nineteen patients with evidence of recurrent tumor on CT or MR images were studied with both ²⁰¹TI SPECT and FDG PET imaging. Two patients were examined twice, so a total of 21 studies were evaluated. The ²⁰¹TI SPECT and FDG PET examinations were performed on the same day in 17 patients, and the remaining four examinations were done within 1 week of one another. Three reviewers independently interpreted each TI SPECT and PET scan. Inappropriate regional increases in ²⁰¹TI or FDG activity were considered indicative of tumor recurrence. Sensitivity and specificity values were based on biopsy results and clinical follow-up. The final diagnosis was tumor recurrence in 16 cases and radiation necrosis in 5 cases. The relationship of scan results to survival was analyzed. RESULTS. The sensitivity and specificity of the ²⁰¹TI examination for detecting tumor recurrence were 11 (69%) of 16 and two (40%) of five, respectively; values for the FDG PET examination were 13 (81%) of 16 and 2 (40%) of 5, respectively. In patients with recurrent tumors less than 1.6 cm in size, results were false-negative in four ²⁰¹TI SPECT examinations and three FDG PET studies. All tumor lesions 1.6 cm or larger (n = 8) were detected. Agreement among the three nuclear medicine specialists was complete for each of the ²⁰¹TI SPECT scans. There was disagreement on the interpretation of five (24%) of the 21 FDG PET scans, which was resolved by consensus. Scintigraphic findings did not correlate with patients' survival times. CONCLUSION. We were unable to detect a statistically significant difference in sensitivity or specificity between the ²⁰¹TI SPECT and FDG PET scans. Both techniques were sensitive for tumor recurrence with lesions less than 1.6 cm or larger. However, given the greater availability, simplicity, and ease of interpretation and the lower cost of the ²⁰¹TI SPECT studies, this technique should be considered for detection of tumor recurrence with lesions that are demonstrated to be 1.6 cm or larger on CT or MR examinations.