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.

A comparison of chemical and ionization dosimetry for high-energy x-ray and electron beams.

A comparison was made of ferrous sulfate (Fricke) and ionometric methods for determining the absorbed dose in a phantom irradiated with 4-MV x-rays, 25-MV x-rays, or electron beams having various incident energies between 10 and 32 MeV. Both chemical and ionization instruments were calibrated in a 60Co beam at a point in water where the absorbed dose had been previously determined. The chemical yield measurements were corrected for spatial variations in dose within the volume of the solution and used to obtain a value of the absorbed dose for each of the x-ray and electron beams. The ratios of G-values required for these determinations were taken from ICRU reports 14 and 21. Ionization instrument readings from three types of commercial ionization chambers were used to obtain alternate values of the absorbed dose for each radiation. C lambda and CE values used in determining these ionization values of dose were also taken from the above ICRU reports. For 4-MV x-rays the values of absorbed dose obtained from chemical measurements agreed to within 0.5% with values obtained from ionization measurements; for 25-MV x-rays the chemical values were about 1% higher than the ionization values; for the electron beams the chemical values were 1%-4% below the ionization values. These discrepancies suggest an inconsistency among the recommended G, C lambda, and CE values similar to that which has been noted by other workers.