Direct action of radiation is the dominant process for
Ionizing radiation acts by two methods: Direct and IndirectDirect action is radiation directly causing DNA damage; example: neutrons and alpha paiclesIndirect action is radiation causing free radical production which acts on DNA; example: photons and gamma raysReference: Khan Physics of Radiation therapy; 5th edition
X-rays
Neutrons and alpha paicles
Electrons
Gamma rays
Radiotherapy