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Comparison of 201Tl-chloride SPECT with 99mtc-MIBI SPECT in the depiction of malignant head and neck tumors.

OBJECTIVE
Comparison of 201Tl chloride SPECT (TI-SPECT) with 99mTc-MIBI SPECT (MIBI-SPECT) in the depiction of malignant head and neck tumors was prospectively studied.


METHODS
Forty-one patients with various tumors of the head and neck were included in this prospective study. Histologically, 36 patients had squamous cell carcinomas, 3 undifferentiated carcinomas, 1 transitional cell carcinoma, and 1 MALT lymphoma. All patients underwent a simultaneous dual-isotope SPECT of the head and neck with 201Tl and 99mTc-MIBI. Dual-isotope SPECT for early (n=41) and delayed acquisition (n=21) was performed. Qualitatively, 3 observers evaluated both TI-SPECT and MIBI-SPECT individually. The interpretation criteria were graded as grade 1 (no abnormal increased uptake) to 5 (definitely increased uptake of a degree equal to or greater than that of normal salivary gland). Statistical analysis of the comparison of Tl-SPECT and MIBI-SPECT was performed. The interobserver difference was evaluated using the kappa-coefficient. Quantitatively, T/N ratio (the ratio of the counts in the tumor divided by that in the normal nuchal muscles) and retention index were compared between TI-SPECT and MIBI-SPECT.


RESULTS
On both the early and delayed images, the grades of uptake of the tumor in TI-SPECT were significantly higher than those in MIBI-SPECT by three observers. The grade of Tl-uptake of the tumor on the delayed images was 5 for all observers (kappa-coefficient=1); however, the kappa-coefficient varied from 0.39 to 0.84 in early T1-SPECT, and in early and delayed MIBI-SPECT. Statistical differences in T/N ratio were noted between early TI-SPECT (2.87 +/- 1.19) and MIBI-SPECT (2.48 +/- 1.06), and between delayed Tl-SPECT (2.11 +/- 0.70) and MIBI-SPECT (1.20 +/- 0.48). The retention index or Tl-SPECT (0.81 +/- 0.24) was significantly higher than that of MIBI-SPECT (0.52 +/- 0.15).


CONCLUSIONS
The present study qualitatively and quantitatively showed that 201Tl had higher accumulation in the tumor than 99mTc-MIBI in both early and delayed images.