Clinical evaluation of tumor scanning with 169-Yb-citrate.

169-Yb-citrate was used as the tumor-scanning agent in 360 patients with malignant tumors and in 55 others with benign lesions and the results compared with 67-Ga-citrate studies in other series. In malignant tumors, the overall positive detection rate for ytterbium was 65.3%; in benign lesions, the false-positive rate was 29.1%. Good results were obtained in the extremities, head and neck, and pelvic area. Of all tumors visualized, squamous cell carcinoma was detected most effectively (77.5%). 169-Yb-citrate has a long shelf life, photon peaks of 178 and 198 kev, clears from the blood more rapidly than 67-Ga-citrate and has an extremely low soft-tissue background uptake. Its main disadvantage is its high radiation dose: 1.74 R/500 muCi whole-body and 5.77 R to the bone.