<prompt> Radiation produces its effect on tissue byCoagulation of cytoplasmIncreasing the temperatureCharring of nucleoproteinHydrolysis  <response>: C i.e. Charring of nucleoprotein Radiotherapy is treatment of malignant tumors with ionizing radiation m.c. y raysQ ; which causes excitation or ionization ejection of electron from orbit of electronQ and kills tumor cells by producing double strand breaks in DNA direct or free radicles indirect. So ionizing Radio Therapy acts on tissue by- Excitation of electron to higher energy levels without actual ejection - and Ionization of electron Removal of orbital e-. Ionizing radiation is of two types - electromagnetic on and paiculate radiation. Type Mass Charge Comment Electromagnetic X Ray y ray do X Ray 0 0 not differ except in Gamma Ray 0 0 the source. y rays are produced intranuclearly and X rays are produced extranuclearly i.e. mechanical Paiculate Electron e e -1 ? Proton p 2000xe 1 Exhibit Bragg peak most of energy is given abruptly causing ionization Neutron n 2000xe 0 Cant be accelerated by an electrical field Alpha paicle 2p2n 2 Helium Paicle 8000xe 2p2n - The biological effects produced by a radiation is quantified as relative biological effectiveness RBE, which compairs them to effects produced by 250KV photon radiation as a standard. - RBE value depends on Linear energy transfer LET; is amount of ionization occurring per unit length of radiation tract, dose, dose rate nature of biological system. - Absorption of energy from radiation in tissue leads to ionization or excitation leading to various biological effects Q. - Radiation must produce double-strand breaks not single-strand in DNA to kill a cell. It can indirectly kill by producing free radicles. - Chromosomal abnormalities occur in cells irradiated in G1 Phase of cell cycle before doubling of genetic material. - Chromatid aberration occurs in cells irradiated in G2 Phase. Most sensitive phase to radiation is M G2M interphaseQ. Most resistant phase to radiation is end of S phaseQ. Lymphocyte analysis provides evidence of recent total body exposure. -- Ionization radiation most commonly y raysX rays is used for . It causes excitation and ionization of electron from orbit Vt double strand break in DNA i.e. charring of nucleoprotein and free radical production in tissueQ. 