Use of the Clinac-35 for tissue activation in noninvasive measurement of capillary blood flow.

Through adjustment of operating parameters responsible for the acceleration, steering, and focusing of electrons en route to the target, we have extracted a 30-MV x-ray beam from the Clinac-35 linear accelerator that is suitable for use in photon activation -15O decay studies of tissue perfusion. This beam is significantly more efficient than the "standard" 25-MV beam in producing 15O in situ through activation of tissue oxygen, thereby substantially reducing the dose to tissue required to yield a desired initial 15O activity. Production and characteristics of the higher energy beam are discussed, and data obtained from its application to measurement of capillary blood flow in animal tumors are presented and analyzed.