The relative biological effectiveness of fractionated doses of fast neutrons (42 MeVd→Be) for normal tissues in the pig. I. Effects on the epidermis and dermal vascular/connective tissues

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Abstract
The effects of fractionated doses of fast neurons (42 MeVd .fwdarw. He) on the early epithelial and later dermal response of pig skin have been assessed and compared with those after X irradiation. For the early epithelial reaction, i.e., moist desquamation, the relative biological effectiveness (RBE) of the neuron beam increased with the decreasing size of the X-ray dose/fraction. There was an experimentally observed upper RBE value of .apprx. 2.75 for X-ray doses fraction of between 2 and 5 Gy. For the late reaction of ischaemic dermal necrosis the RBE was > 3.0 for X-ray doses fraction of < 3 Gy and, based on the assumptions made in the linear-quadratic model of cell survival, an upper limiting RBE of 4.32 .+-. 0.39 was calculated for infinitely small doses/fraction. These findings were compared with other radiobiological data and the conclusios drawn from the results of clinical trials. It was concluded that for the sparing of late effects in skin and subcutaneous tissues, relative to acute reactions, a relatively small number of fractions in a short overall treatment time may be optimal for fast neutron therapy.