Neutron imaging using medical linacs

The feasibility of imaging soft tissues with neutrons (neutron radiography) from a medical linac as a complement to the conventional X-ray portal imaging is proven. Both direct and indirect neutron radiographs have been successfully obtained. In the direct method, a film is exposed to the beam through a neutron converter. The latter transforms the neutrons into γ-rays which subsequently darken the film. In the indirect method, a metallic foil is exposed to the neutrons in the beam and subsequently becomes activated. The resulting gamma rays from the decay of the activation reaction are subsequently used to darken a film and produce an image. In addition, because most of the neutrons generated are fast (average 1 to 2 MeV), a fast neutron radiograph has also been successfully obtained using a CR-39 plate. An exit dosimetry method is suggested for boron neutron capture therapy (BNCT) using neutron radiography. In this manner, the concentration distribution of boron-10 and/or the neutron capture dose in the irradiated region can be obtained through proper calibration. Possible clinical applications of neutron radiography with medical linacs are discussed