Chronic blood irradiation: a new approach

Extracorporeal irradiation of blood is beneficial in suppressing early rejection of renal allografts and in treating chronic lymphocytic leukemia. Previously, nearly all blood irradiation has involved brief intermittent exposures with high dose rates. The small amount of data available involving chronic irradiation suggests that doses given chronically at lower rates are more effective in suppressing graft rejection. However, no suitably portable device has been available to permit chronic irradiation. This work has been directed toward developing a fully portable irradiator. After preliminary testing of a variety of source materials, 170Tm was selected for its favorable beta energy, low cost, and compatibility with the fabrication requirements. The body of the irradiator is cast from polyfurfuryl alcohol with subsequent high-temperature conversion to vitreous carbon. By sequential layering of the alcohol and suspending of 169Tm2O3 in the midlayer, a unit is produced without any radiation exposure and with the source material contained on both a macro and a micro scale. Exposure of the unit to reactor neutrons produces 170Tm without activation of the vitreous carbon. A 170Tm irradiator giving a transit dose of 16 rads (100 ml/min flow) was connected in a carotid--jugular shunt on a 20-kg goat. Lymphocyte levels decreased to about 15 percent of the preexposure level during the first week and thereafter slowly rose to about 50 percent of preexposure levels 2 months after exposure. Reciprocal skin grafts made at the end of irradiation (12 days) were rejected at 12 days on the nonirradiated control and at 24 days on the irradiated goat. These results are consistent with data reported on chronically irradiated baboons even though the dose rate for the present test was only about one-fourth that for the baboons