Fudan University Shanghai Cancer Center particle beams electron(β particle) energy transferred per unit track length of radiation a particle neutron Low LET beams(10kev/um) negative pion X ray Ray proton electron Photon beams High let beams(>10kev/u m) neutron ra y negative pion yray proton 复旦大学上海医学院肿瘤学糸particle beams electron ( particle)  particle neutron negative pion proton linear energy transfer (LET) energy transferred per unit track length of radiation Low LET beams (<10kev/μm) X ray  Ray electron High LET beams ≥10kev/μm) neutron negative pion proton 复旦大学上海医学院肿瘤学系 Fudan University Shanghai Cancer Center