Comparative evaluation of ²⁰¹Tl SPECT and CT in the follow-up of irradiated brain tumors

Background

Radiation-induced changes in post-irradiated brain tumors may produce morphological alterations similar to those of tumor recurrence on computed tomography (CT). However, ²⁰¹Tl single-photon-emission computed tomography (SPECT), with its ability to image metabolic changes, may differentiate post-irradiated gliotic changes from metabolically active congregations of viable tumor cells. This study was carried out to compare these two imaging modalities for the follow-up evaluation of post-irradiated brain tumors.

Methods

Thirty-five patients with previously irradiated primary brain tumors were evaluated for this study. ²⁰¹Tl SPECT and CT were carried out during follow-up, which ranged from 3 to 125 months (median, 18 months). These findings were compared with the clinical outcome, as observed during the subsequent follow-up.

Results

Sensitivity, specificity, and the overall accuracy of ²⁰¹Tl SPECT were 82.7%, 83.3%, and 82.8%, compared to 58.6%, 66.6%, and 58.3%, respectively, for CT. Post-scan progression-free survival (PFS) was significantly different for those patients having positive and those having negative evidence of tumor recurrence based on the imaging studies during follow-up. However, PFS was better correlated with ²⁰¹Tl SPECT results than with the CT results. With ²⁰¹Tl-SPECT, median PFS was 4 months for those with positive reports, versus 33 months for those with negative reports (P = 0.003), compared to a corresponding median PFS of 3 months versus 14 months (P = 0.025), respectively, with CT. On multivariate analysis, age and ²⁰¹Tl SPECT were the only significant variables for predicting post-scan PFS.

Conclusion

²⁰¹Tl SPECT, with its ability to be taken up by viable tumor tissues, is superior to CT for the follow-up evaluation of post-irradiated brain tumors.