[en] When a patient is irradiated with bremsstrahlung of energy greater than about 10 MeV, high LET particles are produced through photonuclear reactions in the tissue and contribute an additional dose to the patient. The absorbed dose contribution due to secondary neutrons is estimated to be 2.2 x 10^-₄, 3.8 x 10^-₄, 5.2 x 10^-₄ and 6.2 x 10^-₄ Gy per photon Gy at 24, 26, 28 and 30 MeV respectively. Based on an absorbed dose of 2.2 x 10^-₄ Gy per photon Gy due to photoneutrons, the absorbed dose due to photoprotons to 6.5 x 10^-₄ Gy per photon Gy, and that due to photoalpha particles is 0.7 x 10^-₄ Gy per photon Gy