Radionuclide production and partial radiochemical characterization following fast neutron irradiation of mouse spleens.

When radiotherapy patients are irradiated with fast neutron beams (energies greater than 20 MeV), positron emitting radionuclides (15O, 13N, 11C) are created in their tissues. Capillary blood flow can be determined in the irradiated tissue by measuring the washout of the 15O. The chemical form of these positron emitting nuclides is important when assumptions about their transport in the development of a blood flow model are being made. In the present work, normal mouse spleen tissue was used as a model system for these studies. The mouse spleen was activated by whole mouse irradiation using the M.D. Anderson Hospital neutron beam produced by 42 MeV protons impinging on a beryllium target. Results of cellular studies and large molecule precipitation measurements (1) show that at least 65% of 15O created in situ in mouse spleen is capable of being transported out of the spleen by the blood supply, (2) suggest that 13N may be 100% biologically mobile, and (3) indicate that 11C appears to be evenly divided between a population associated with small biologically mobile molecules and a population associated with larger, biologically trapped or immobile molecules.