Relative biological effectiveness (RBE) of 50 MV (Be) neutrons for acute and late skin injury

Fractionated doses of E_d = 50 MeV (D-Be) neutrons and γ-rays were delivered to areas of pigs' skin. Acute response was measured in terms of desquamation, and late (several months) response as degree of contraction relative to control areas. The RBE _{n γ} for late effects was higher than for acute effects in skin, regardless of fractionation pattern of neutrons (twice or four times weekly). γ -ray dose fractions of 200 rad (5 times weekly) are equivalent, for late effect, to neutron dose fractions less than 65 rad, while, for acute effect, equivalence is achieved at neutron doses greater than 72 rad. The difference is probably the result of increased absorbed dose in subcutaneous fat with neutron irradiation.