DIAGNOSIS OF RECURRENT BRAIN-TUMOR - VALUE OF (TI)-T-201 SPECT VS F-18 FLUORODEOXYGLUCOSE PET

OBJECTIVE. This prospective study was designed to compare the sensitiv ity and specificity of a relatively simple examination, Tl-201 chlorid e single-photon emission CT (SPECT), with a more complex examination, F-18-fluorodeoxyglucose (FDG) positron emission tomography (PET), in p atients thought to have recurrent brain tumor. Because both agents hav e 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 Tl-201 SPECT and FDG PET imaging. Two patients were examined twice, so a total of 21 studies were evaluated. The Tl- 201 SPECT and FDG PET examinations were performed on the same day in 1 7 patients, and the remaining four examinations were done within I wee k of one another. Three reviewers independently interpreted each TI SP ECT and PET scan. Inappropriate regional increases in Tl-201 Or FDG ac tivity were considered indicative of tumor recurrence. Sensitivity and specificity values were based on biopsy results and clinical follow-u p. 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 Tl-201 exami nation for detecting tumor recurrence were 11 (69%) of 16 and two (40% ) of five, respectively; values for the FDG PET examination were 13 (8 1%) of 16 and 2 (40%) of 5; respectively. In patients with recurrent t umors less than 1.6 cm in size, results were false-negative in four Tl -201 SPECT examinations and three FDG PET studies. All tumor lesions 1 .6 cm or larger (n = 8) were detected. Agreement among the three nucle ar medicine specialists was complete for each of the Tl-201 SPECT scan s. There was disagreement on the interpretation of five (24%) of the 2 1 FDG PET scans, which was resolved by consensus. Scintigraphic findin gs did not correlate with patients' survival times.: CONCLUSION. We we re unable to detect a statistically significant difference in sensitiv ity or specificity between the Tl-201 SPECT and FDG PET scans. Both te chniques were sensitive for tumor recurrence with lesions less than 1. 6 cm or larger. However, given the greater availability, simplicity, a nd ease of interpretation and the lower cost of the Tl-201 SPECT studi es, this technique should be considered for detection of tumor recurre nce with lesions that are demonstrated to be 1.6 cm or larger on CT or MR examinations.