Dynamic studies of positron-emitting putative tumor marker 132Cs in mice show differential tumor and regional uptake.

Positron-emitting 132Cs (t1/2 = 6.47 days) was generated from stable 133CsCl via the 133Cs (p,pn) 132Cs reaction. BALB/c mice, bearing implanted MT296 mammary tumors, were given 4.6 mEq kg-1 of 132CsCl via a single intraperitoneal injection. Postinjection uptake of 132Cs into body regions was monitored in vivo with external detectors. Positron emission from the tumor region was continuously greater than that from the head, the numerical ratio of mean emission intensities being fourfold at 10 min postinjection. Tissues excised from these mice postmortem showed sequence of relative tissue cesium uptake rates to be kidney 1.8, small intestine 1.7, tumor 1.0, skin 0.75, liver 0.75, skeletal muscle 0.4, and brain 0.28. Comparative studies with multiple injections of stable cesium and rubidium showed this sequence to be ion-specific. These observations suggest that positron-emitting isotopes of cesium could provide useful markers for tumors of several tissues.