RADIATION ONCOLOGY - McMaster University放射肿瘤学-麦克马斯特大学.ppt

RADIATION ONCOLOGY An Introduction by W.G. McMillan Radiation What is it? How does it work? Why do it? How do we measure it? How do we deliver it? How is it different from getting an X-ray? Physical Considerations Excitation an electron in an atom or molecule is raised to a higher energy level without being ejected Ionization an electron in an atom or molecule is given enough energy to be ejected. in living material, this releases enough energy locally to break biological bonds. C=C requires 4.9 eV and 1 ionization event provides ~ 33 eV. Ionizing Radiation Electromagnetic waves of wavelength ?, frequency v, velocity c where ? v = c and c = 3 x 1010 cm/sec ?-rays: radioactive decay of unstable nucleus x-rays: produced by electrical device photons: packets of energy where E = hv where h = Planck’s constant using both equations if ? is long, then v is small and E is small Electromagnetic Spectrum Ionizing Radiation Particulate electrons: small negatively charged particles can be accelerated to almost the speed of light. protons: positively charged particles , mass ~ 2000 times greater than electron ? particle: nucleus of helium atom = 2 protons + 2 neutrons ( ie decay of radium-226 to radon-222) heavy charged ions: nuclei of elements C, Ne, Argon, etc. Photon Interaction With Matter: Photoelectric Effect ? Z First Radiograph: 1896 Photon Interaction With Matter: Compton Effect Independent of Z Portal Image Biological Considerations Radiation Interaction with biological materials Cell Survival Curves Repair of Radiation Damage Effect of oxygenation on radiation damage Cell cycle considerations Pharmacological modification of radiation effects Radiation Interaction With DNA Indirect Interaction fast electron hits H2O ? H2O+ + e-; H2O+ + H2O ? H3O+ + OH- reactive species interact with DNA Direct Interaction photons (rarely) or particles (always) directly interact with DNA Direct vs Indirect Action of Radiation on DNA Human Chromosomes With and Without Radiation Su