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High specific activity is not optimal: 18 F-fluoroestradio positron emission tomography-computed tomography results in a breast cancer xenograft.

The purpose of the preliminary study was to investigate whether high specific activity (SA) of 18 F-fluoroestradiol was optimal in breast cancer diagnosis. Imaging at variable SA was conducted in a ZR-75-1 xenograft model of estrogen-receptor positive human breast cancer in 6 mice. The region of interest was manually drawn, and the percent of injected dose per gram of the tumor and muscle in the regions of interest were recorded. Tumor-to-muscle ratio (T/M) was calculated and compared in each group with different SAs. In addition, the correlation between blood estradiol and sex hormone-binding globulin and the value of T/M were also analyzed. The value of T/M increased initially with the rise of SA and it reached the peak at SA of 1.6 Ci/μmol. After that, the value fell down sharply and remained stable from SA of 3.1 Ci/μmol. The value of T/M was highest at SA of 1.6 Ci/μmol (P < .001). Additionally, the blood levels of estradiol and sex hormone-binding globulin showed no correlation with the value of T/M (P > .05). High SA of 18 F-fluoroestradiol leads to low T/M results in breast cancer xenograft models. We should control SA in a reasonable range to obtain high-quality images.