INTRAOPERATIVE BETA-PROBE - A DEVICE FOR DETECTING TISSUE LABELED WITH POSITRON OR ELECTRON EMITTING ISOTOPES DURING SURGERY

An intraoperative beta probe was designed, built, and tested for detec tion of radio-labeled malignant tissues that has the advantage of bein g selectively sensitive to beta while insensitive to gamma radiation. Since beta radiation (electrons or positrons) has a short range in tis sue, this probe is ideal for detecting tracers in tumors at the surfac e of the surgical field. This probe contains a plastic scintillation d etector sensitive to beta rays and to a lesser degree some background gamma rays. A second detector counts spurious gamma rays and allows fo r their subtraction from the activity measured by the first detector. Sensitivity of the dual probe for I-131 and F-18 was measured to be 10 8 counts/s/kBq (4000 counts/s/mu Ci). The dual-detector probe faithful ly measured the 10:1 ''tumor'' to background ratio of radioactivity co ncentrations in a simulated environment of a tumor in the presence of intense background 511 keV photons. In another phantom experiment, sim ulating abdominal tumor deposits with various realistic I-131 radioact ive concentrations, the probe was able to accurately identify tumors o f approximately 50 mg with a tumor/normal radioactivity concentration of 3/1 in 10 s.