Fast Neutron Therapy Although not commonly used, fast neutron therapy is another area of interest, as neutrons have a high have a high LET and RBE despite not exhibiting a Bragg peak ([10]). Keywords: particle; carbon; helium; neutron; heavy ions; radiation EN particle carbon helium neutron heavy ions radiation 1 2 2 07/31/21 20210729 NES 210729 Overview Radiation therapy is a cornerstone modality in the treatment of malignant diseases.