Damage to mouse lung with fractionated neutrons and x rays

The relative biological effectiveness (RBE) for damage to mouse lung was measured for single doses and up to 30 fractions of 8 MV x rays and fast neutrons, relative to 250 kVp x rays. With 8 MV x rays the RBE was 0.87 and did not vary with dose per fraction between 150 and 1200 rad. With fast neutrons the RBE did not vary from 1.5 at 1200 rad of x rays, which is about 30% lower than that for skin, to 3.7 at 150 rad of x rays, which is about 10% less than that for skin. The implications for treatment of the lung with fast neutrons are discussed.