Spallation-produced thulium-167 for medical applications

The biokinetics and organ distribution of 139Ce, 143Pm, 144Pm, 146Eu, 147Eu, 153Tb, 155Tb, 167Tm, 172Lu and 173Lu were investigated in normal, tumour (virus-induced mammary carcinoma, UV-induced UVT 14306 sarcoma, chemically induced DMBA 788 sarcoma), and aseptic inflammation-bearing male XVII/B1n strain mice. The radiolanthanides were accumulated in all investigated tumours. A blood activity decrease of 0.006-0.01% of the injected dose was generally observed during 72 h. When the individual nuclides were compared, the biological characteristics and the decay properties were most favourable in the case of 167Tm with regard to tumour imaging. Satisfactory scintigrams were obtained already 4-6 h after administration. Thulium-167 showed tumour/blood ratios of 1.5-3.0 5 h and 20-30 24 h p.i. respectively. The tumour/muscle ratios (12.0+-2.0 for the UVT 14306 sarcoma and 10.0+-1.5 for the DMBA 788 tumour) remained constant between 5 and 50 h. Because of the higher skeletal uptake (about 40% of the injected dose), the tumour/bone ratios did not exceed a value of 1. Thulium-167 is not tumour specific. As in the case of 67Ga and 111In, a considerable uptake in inflammations was observed. The elimination of the 167Tm-activity from these lesions was slower than for tumours. Preliminary clinical studies showed satisfactory delineations of human tumours in the cranial, thorax and abdominal region. Thulium-167 offers advantages in soft tissue tumour imaging, especially in the abdominal region. (author)