Abstract |
The purpose of this study is to evaluate the diagnostic
accuracy of various quantitative indices for the
differentiation of benign from malignant primary soft
tissue tumors by FDG-PET. A series of 32 patients with
a variety of histologically or clinically confirmed
benign (20) or malignant (12) soft tissue lesions were
evaluated with emission whole body (5min/bed position)
PET after injection of [18F]FDG. Regional 20min
transmission scan for the attenuation correction and
calculation of SUV was performed in 16 patients (10
benign, 6malignant) followed by dynamic acquisition for
56min. Postinjection transmission scan for the
attenuation correction and calculation of SUV was
executed in the other 16 patients (10 benign, 6
malignant). The following indices were obtained : the
peak and average SUV (pSUV, aSUV) of lesions, tumor-to-
background ratio acquired at images of 51 min p.i.
(TBR51), tumor-to-background ratio of areas under time-
activity curves (TBRarea) and the ratio between the
activities of tumor ROI at 51 min p.i. and at the time
which background ROI reaches maximum activity on the
time-activity curves (T51/Tmax). The pSUV, aSUV, TBR51,
and TBRarea, in malignant lesions were significantly
higher than those in benign lesions. We set the cut-off
values of pSUV, aSUV, TBR51, TBRarea and T51/Tmax for
the differentiation of benign and malignant lesions at
3.5, 2.8, 5.1, 4.3 and 1.55, respectively. The
sensitivity, specificity and accuracy were 91.7%,
80.0%, 84.4% by pSUV and aSUV, 83.3%, 85.0%, 84.4% by
TBR51, 83.3%, 100%, 93.8% by TBRarea and 66.7%, 70.0%,
68.8% by Tsl/Tmax. The time-activity curves did not
give additional information compared to SUV or TBR. The
one false negative was a case with low-grade
fibrosarcoma and all four false positives were cases
with inflammatory change on histology. The visual
analysis of FDG-PET also detected the metastatic
lesions in malignant cases with comparable accuracy. In
conclusion, all pSUV, aSUV, TBR51, and TBRarea are
useful metabolic semi-quantitative indices with good
accuracy for the differentiation of benign from
malignant soft-tissue lesions. |