Exploiting the unique interaction characteristics of fast neutrons for improved cancer therapy: A radiobiological perspective

Fast neutrons have sufficient energy to liberate recoil protons, alpha particles, and other products when they interact with the nuclei of the target material through scattering and absorption processes. Physical interactions with biological tissues occur mainly with hydrogen nuclei and as the protons interact with the hydrogen in tissues, they create dense ionization chains along their tracks thus depositing energy. Fast neutron therapy was pioneered by Robert Stone in 1938 a few years after the discovery of the neutron. Its main advantage is the limited sensitivity to hypoxia and treatment of slow-growing tumors hence better local control. This is where photon therapy has yet to have much success. Energy deposition by fast neutrons in living tissues is higher than in conventional radiotherapy using mega voltage (MV) photon beams. This higher energy deposition gives fast neutrons a higher relative biological effectiveness (RBE) in dealing with certain tumors. Fast neutrons also have a higher linear energy transfer (LET) and can reach deep-sited tumors better than photon therapy. The main challenge with Fast neutron therapy has been extreme toxicity in late-reacting tissues. Overall, fast neutron therapy holds potential for the treatment of certain tumors by leveraging the unique interaction characteristics of fast neutrons with biological tissues. This review therefore intends to bring this uniqueness to light to enhance the understanding of the radiobiological properties of fast neutrons and the advantages associated with its therapy.