Charged photoparticle production in tissue during radiotherapy.

Photon-induced proton and alpha particle production in tissue is estimated for the photon energy range from 3 to 28 MeV, using the authors' previously established methods. It is shown that charged particle emission exceeds neutron emission for energies greater than 11 MeV by a factor that reaches a maximum of 7.0 at 17 MeV. Due to uncertainties in the source data this maximum value should be regarded as indicative only. Above 17 MeV the neutron yield rises sharply and the ratio of charged particle emission to neutron emission declines to values of 3.0 and 1.7 at 20 and 28 MeV, respectively.