Microdosimetry of a 42 MeV therapy neutron beam.

Radiation quality of fast neutron therapy beams can change with depth. For a neutron beam generated by p----Be, the primary effect is a "hardening" of the neutron beam produced by the scattering of slow neutron components. A 42 MeV neutron therapy beam was investigated using microdosimetric techniques. We report measurements of dose mean and saturation-corrected lineal energy in water phantom at build-up depth, 5, 15, and 30 cm, and show representative logarithmic dose distributions in lineal energy. RBE is also calculated using assumptions based on the Theory of Dual Radiation Action and presented as a function of dose and depth.