Fast neutron beam activation in situ for tumor blood flow determination

A novel method to determine regional blood flow, is applicable to cancer patients receiving photon radiation therapy at energies greater than 25MW, using in situ produced radioactivities and measuring disappearance of annihilation radiation from the tumor volume, which is due to decay and to transport of radio-activity from the field of view. The present work considers in situ production of radioactivity by a clinical fast neutron beam. In a p(43) Be(22) beam, /sup 11/C, /sup 13/N, and /sup 15/O are produced when tissue is irradiated. A treatment of 100 cCy produces millicurie amounts, adequate to examine the mobile component of the induced activity on its first pass through the heart. The yields of positron emitters from fast neutron irradiation of carbon, hydrazine, and water targets was measured thus separately accounting for radioactivities from the principal elements of blood and tissue. To evaluate the dynamics of radioactivity in the heart, a phantom was constructed in which tissue equivalent liquid was circulated and neutron activated in a ''tumor volume'', then passed to a ''heart'' and from there to the circulatory system with only a small fraction returning to the tumor volume. Positron decay rates vs time were measured in the ''tumor'' volume and in the ''heart'' for various flow rates