Diffusion rates of positron emitters in pion irradiated patients

Positron emission tomography has been used for visualising the stopping distribution in patients irradiated with negative pi-mesons. The biological half-life of the activation within irradiated tumours of the rectum, pancreas, lung wall, head and neck has been measured. Patients were placed in a positron (β+) spectrometer immediately after treatments of approximately 0.7 Gy nominally at the pion peak. Counting began approximately five minutes after a 15 minute irradiation. The biological half-life of the activated β+-emitting radionuclides depended on the anatomical site, ranging from 38 to 79 minutes for the sites measured. The abdominal tumours had greater diffusion rates than the more solid tumours in the other sites. This result was consistent with the expectation that increased vascularity should increase diffusion. (U.K.)