99mTc-MIBI and 201Tl SPET in the detection of recurrent brain tumours after radiation therapy


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Abstract

The purpose of this study was to evaluate whether 99mTc-hexakis-2-methoxyisobutylisonitrile (99mTc-MIBI) or 201Tl single photon emission tomography (SPET) could detect recurrent tumours in patients with previous radiation therapy for brain tumours. Dual SPET with 99mTc-MIBI and 201Tl was performed in 21 patients suspected of having recurrent brain tumours. SPET images were acquired 15 min (early) and 2 h (delayed) after injection. The ratio of the average counts for the region of interest in the lesion area and its mirror image in normal brain tissue was obtained. Early and delayed ratios were calculated. On the basis of histological and/or clinical findings, the final diagnosis was considered as recurrent tumours in 15 patients and radiation necrosis in six. Both ratios using 99mTc-MIBI and 201Tl were significantly higher in recurrent tumours than in radiation necrosis. Based on a cut-off of 5.89 of the early ratio using 99mTc-MIBI to distinguish between recurrent tumours and radiation necrosis, the accuracy was 90%. Based on a cut-off of 6.77 of the delayed ratio using 99mTc-MIBI, the accuracy was 86%. The corresponding values using cut-offs of 2.40 and 1.85 with 201Tl were 90% and 86%, respectively. However, within recurrent tumours, both ratios for 99mTc-MIBI were significantly higher than those for 201Tl. Early 99mTc-MIBI SPET may be especially useful for the detection of recurrent tumours in patients who have previously undergone radiation therapy for brain tumours.

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