Induced radioactivity in patients from betatron irradiation.

Abstract

The nuclear binding energy averages 7–8 MeV per nucleon. If a nucleus is penetrated by a quantum of energy which exceeds this average binding energy, the nucleus may lose one or more of its nucleons. The residual nucleus may be radioactive. As early as 1949, induced radioactivity in tissue from a 24 MeV synchrotron was demonstrated by Mayneord et al. (1949). This induced radioactivity results from the nuclear photo-effect and accounts for less than 1% of the total energy absorbed from a bremsstrahlung spectrum whose average energy is 10 to 15 MeV (Joyet, 1965). Since this correlates with energy levels used clinically in betatron irradiation, the induced activity may be useful in clinical applications, including correlation of the activity distribution and ultimately the dose distribution with that prescribed by the clinician. A similar visualization procedure for a therapeutic proton beam has been demonstrated using an on-line positron camera (Bennett et al., 1978). The 33 MeV Brown Boveri betatron at Mon...