A Cf-252-based instrument for in vivo body protein monitoring in cancer patients

A hospital-based facility for in vivo prompt gamma neutron activation analy sis of nitrogen for body protein determination is described. The patient is laid on a movable couch and is scanned with a vertically collimated neutro n beam from a Cf-252 neutron source (the amount of Cf varying from 120 to 4 0 mu g due to the physical decay) positioned below the patient. Four large NaI(Tl) detectors are used to measure the 10.8 MeV gamma-rays from nitrogen . To check the long-term stability of the system, a solid phantom simulatin g the geometry of the adult human trunk. having similar elemental compositi on as tissue. was constructed. Repeated phantom measurements over 6 months gave a reproducibility in nitrogen determination of 2.9% (1 SD). Duplicate patient measurements carried out within a week showed a reproducibility of 5% (1 SD). A calibration method for absolute protein measurements in patien ts is presented. Patients are normally measured for 40 min; giving a mean w hole-body equivalent dose of 0.25 mSv. Results from measurements on 13 canc er patients are presented.