The lethal effects of Fermilab fast neutrons vary with the depth of cells in a water phantom.
Using V79 Chinese hamster lung fibroblast cells grown in culture we have examined the lethal effects of fast neutrons from the Fermilab therapy facility as a function of depth in a water phantom. Exposures and dosimetry were performed from 3 to 24 cm deep in the phantom along the central axis of the neutron beam, using various collimator configurations. The results indicate that the relative biological effect (RBE), using 60Co gamma rays as the standard radiation, varies with depth in the neutron beam. Starting from d-max (approx. 3 cm), the RBE appears to decrease continuously with depth. At 24 cm deep, the relative effectiveness is 10-15% lower than at 3 cm deep. There appears to be no systematic variation of relative effectiveness with shape or size of collimator. If a hydrogenous filter is added before the beam passes into the water phantom, the variation with depth is greatly reduced.
Hill
C K
CK
Radiation Oncology Department, University of Southern California School of Medicine, Albert Soiland Cancer Research Laboratory, Los Angeles 90015.
Ten Haken
R K
RK
Awschalom
M
M
D000818:Animals; D002470:Cell Survival / Q000528:radiation effects*; D005214:Fast Neutrons; D066298:In Vitro Techniques; D008961:Models, Structural; D012062:Relative Biological Effectiveness; D014867:Water
D014867:Water