The Application of ^<203>Pb for Radiopharmaceuticals

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The radionuclide ^<203>Pb decays completely by electron capture to stable ^<203>Tl with a halfーlife of 52 hours. The present study was undertaken to investigate the application of ^<203>Pb for radiopharmaceuticals (especially tumor imaging agent).^<203>Pbーchloride solution was injected into the tumorーbearing rats, tumor-bearing mice and inflammatoryーinduced rats. These animals were killed at various time intervals from 3 hours to 48 hours. Tumor tissue and normal tissues were excised. The retention values of ^<203>Pb in the tissues were calculated against the administered dose of ^<203>Pb. The results obtained from the experiments about ^<203>Pbーcholoride were compared with previously described results of ^<67>Gaーcitrate and ^<201> Tlーchloride. In addition, bio-distribution of ^<203>Pb in animal body was observed by whole body autoradiography and that of this nuclide in tumor tissue was observed by macro-auto-radiography. Subcellular distribution of ^<203>Pb in tumor tissue was determined by the modified method of Hogeboom and Schneider.Retention values of ^<203>Pb in tumor tissue was smaller than those for ^<67>Ga, and much larger than those for ^<201>Tl. But retention values of ^<203>Pb in inflammatory tissue were smaller than those for ^<67>Ga and ^<201>Tl. The avid uptake of ^<203>Pb in bone and the uptake of this nuclide in tumor and liver were observed by whole body autoradiography. Accumulation of this nuclide in viable tumor tissue was observed by macroautoradiography.From the results described above, it was deduced that ^<203>Pbーchloride was a potential tumor imaging agent which hardly accumulated in inflammatory tissue.