Correlation of the findings of thallium-201 chloride scans with those of other imaging modalities and histology following therapy in patients with bone and soft tissue sarcomas

We performed a prospective study to evaluate the imaging potential of thallium-201 as compared with other imaging modalities in differentiating residual/re-current tumors from post-therapy changes in patients with musculoskeletal sarcomas.²⁰¹TI scans, magnetic resonance imaging (17), X-ray computed tomography (6) or contrast angiography (6) studies in 29 patients previously treated for musculoskeletal sarcomas were correlated with either histopathologic findings (26 patients) or 2-year clinical follow-up (three patients). All imaging studies were acquired within 2 weeks. Ratios of²⁰¹T1 tumor uptake to the contralateral (28 patients) or adjacent region of interest were calculated. When qualitative interpretation was in doubt, only those cases with a ratio of 1.5 or more were considered suggestive of recurrent or residual viable tumor tissue. Residual or recurrent tumor tissue was verified in 21 patients by biopsy. All had true-positive²⁰¹Tl scans while the other imaging modalities were true-positive in 20 and equivocal in one. In eight patients, there was no evidence of viable tumor tissue as proven by biopsy in five and long-term clinical follow-up in three.²⁰¹Tl scan was false-positive (ratio 1.5) in one patient and true-negative in seven while the other' imaging modalities had four false-positives. The average²⁰¹T1 ratios were 3.8±1.1 in the true-positive cases and 1.3±0.3 in the true-negative cases. The percentage sensitivities, specificities, and accuracy for²⁰¹T1 were 100%, 87.5%, and 96.5% versus 95%, 50%, and 82.7% respectively for other imaging modalities These results indicate that²⁰¹T1 scintigraphy is more accurate than other imaging modalities in differentiating residual/recurrent musculoskeletal sarcomas from post-therapy changes.