The response of haemopoietic colony-forming units and lymphoma cells irradiated in soft tissue (spleen) or a bone cavity (femur) with single doses of X rays, γ rays or D-T neutrons

A comparison of the effects of single doses of 300 kV X rays, 137Cs γ rays, 60Co γ rays and 14 MeV D-T neutrons on haemopoietic stem cells and lymphoma cells in the mouse has shown the following: (1) For the cell types used, significantly different RBE (γ/X) values are obtained in soft tissue which depend on the nature of the cells and their state of proliferation. (2) The data suggest that stem cell regeneration occurs close to bone surfaces. (3) Cells irradiated in the femur are less sensitive to neutrons (a factor 0·88 ±0·04 for lymphoma cells) than cells irradiated in the spleen or in suspension. (4) The effect of a first dose of radiation on normal haemopoietic tissue may be different from that of succeeding doses (as during fractionation), depending on the type of radiation and the size of the doses. (5) A comparison of the effects of radiation on the different cell types used in the present experiments has shown that, in general, single doses of fast neutrons are no worse (in damaging normal cells compared with malignant cells) than single doses of conventional low LET radiation. The implications of the findings for radiotherapy are discussed.