Radiation produces its effect on tissue by
C i.e. Charring of nucleoprotein Radiotherapy is treatment of malignant tumors with ionizing radiation (m.c. y rays)Q ; 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 Can't be accelerated by an electrical field Alpha paicle 2p+2n +2 Helium Paicle (8000xe) (2p+2n) - 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 rays/X 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.
Coagulation of cytoplasm
Increasing the temperature
Charring of nucleoprotein
Hydrolysis