Generally, it is reported that the smallest tumor that can be detected with the 67Ga scintigram is limited to a diameter of approximately 3.0 cm. To surmount that limitation we have attempted to detect small lung cancer by means of quantitative external counting of 67Ga uptake rather than the qualitative scintigram.
Seventy-two hours after 67Ga injection, the uptake counts of tumor (T) and a corresponding normal region in the opposite lung (N) were measured with scintillation camera. The 67Ga uptake ratio ( (T-N) /N) could then be calculated. The 67Ga uptake ratio of 6 pulmonary adenocarcinomas was measured to be 0.05-0.22. In contrast, the 67Ga uptake ratio of benign lesions such as tuberculoma, pulmonary infarct, cyst, pneumoconiosis, mucoid impaction, hamartoma and chronic inflammatory lesion with calcification resulted in negative values (-0.01--0.77) . From these results, it was possible to differentiated small adenocarcinoma of the lung tumor from these benign diseases.
However, the 67Ga uptake ratios of 4 cases of active tuberculosis, 5 chronic inflammatory lesions and 1 granuloma were 0.01-0.41. The cases with more than 0.30 of 67Ga uptake ratios all represented active inflammatory lesions. However, there were some cases of inflammatory lesions where the values overlapped with adenocarcinoma.
