RT24: Radiation Therapy Prelim - History, Atom & Radioactivity (PDF)

RT24: Radiation Therapy 1st Sem, A.Y. 2024-2025 Radiation Therapy Treatment of disease, primarily malignant tumors, using ionizing radiation Aim To deliver a precisely measure dose of radiation to a defined tumor volum...

RT24: Radiation Therapy 1st Sem, A.Y. 2024-2025 Radiation Therapy Treatment of disease, primarily malignant tumors, using ionizing radiation Aim To deliver a precisely measure dose of radiation to a defined tumor volume with as minimal damage as possible to the surrounding tissue, resulting in the eradication of the tumor, a high quality of life, and prolongation of survival at a reasonable cost. Historical Development Discovery of Radiation 400 BC 1869 1895 Greeks Dmitri Mendeleev Wilhelm Conrad Roentgen Crooke’s Tube X-ray Exposure 1896 1897 1898 Antoine Henri J.J. Thomson Marie and Pierre Becquerel Curie 1900 1905 1911 Paul Villard Albert Einstein Ernest Rutherford 1913 1920 1932 Neils Bohr Ernest Rutherford James Chadwick Hans Geiger William Coolidge Modalities Image-intensifier Tube Computed Positron-emission Diagnostic Tomography Tomography Ultrasonography Magnetic Resonance Imaging 1950s-1960s 1970s-1980s 1990s-2000s Early Cases for Radiation Oncology Emil Grubbe (last days of January 1896)- first treated the recurrent breast cancer of a 55-year old woman John Daniel (1896)- described scalp epilation during a diagnostic exposure  Leopold Freund (November 1896, Vienna)- irradiation of a four-year old girl with an extensive dorsal hairy nevus; immediate result led a normal life, bearing a healthy son. Victor Despeignes (1896)- treated a case of gastric carcinoma William Pusey (1898)- reported beneficial effects on hypertrichosis and acne Early Cures: Thor Stenbeck (1899, Stockholm)- treatment of a 49-year old woman’s basal cell carcinoma of the skin on the nose, delivering over 100 treatments in the course of 9 months; patient known to be living well 30 years later. Tage Sjorgen (1899, Stockholm)- curing of squamous cell epithelioma with 50 treatments over 30 months  Neils Ryberg Finsen (1903)- used UV rays to treat Lupus Vulgaris, which was also used to treat cancer later on. Radioactivity and Radium 1902: The Radium Girls 1928 – 1960s Structure of an Atom  AMU - 1/12 of the mass of a carbon-12 atom - 1.66 x 10^-24 g Nuclear portion (nucleus) - 10^-15 m in diameter Extranuclear portion (shells) - 10^-10 m in diameter  Proton (p) Electron (e-) Neutron (n) Location Nucleus Orbit Nucleus Charge Positive Negative Neutral amu 1.007277 0.000549 1.008665 Atomic Notation A Z X A=Z+N A- atomic mass (number of nucleons) Z- atomic number (number of protons) X- element symbol Electron Shell Pauli Exclusion Formula Max. number of Electrons = 2 (n)^2 Shell Limit K 2 L 8 M 18 N 32 Electron Shell Madelung’s Rule K L M N Activity: Atom Activity: Atom How many electrons are there in the M shell of: Oxygen – 8 electrons Zinc – 30 electrons Technetium – 43 electrons Mass Defect Electron Binding Energy Activity: Mass Defect Calculate the mass defect for lithium-7, with the mass at 7.016003amu. What is the mass defect for U-238? Activity: Binding Energy Based on the values you’ve solved prior, what are the binding energies for: Li-7 U-238 Radioactivity Radioactivity spontaneously give off energy instability in the atom’s nucleus excess energy Sources of Instabilities Too big Too many neutrons for the protons. Not enough neutrons for the protons. Natural Too much excess energy Radioactivity Artificial Activity: Radioactivity What is the difference between natural and artificial radioactivity? When does a nuclide undergo radioactive decay and what are they called afterwards?  Radiation is a form of energy traveling through a medium or space. It travels as waves or subatomic particles through air, water or solid materials. Forms of Radiation A. Particulate- α, β, η B. Electromagnetic - X-ray, Gamma-ray (γ), UV, Infrared, Microwave, Visible light, Radiowave  Types of Radiation (according to damage it could or not incur) A. Ionizing B. Non-ionizing Physical Properties of a Radioactive Material The Decay/ Disintegration/ Transformation Constant () - The fraction or percentage of the original number of radioactive atoms decaying per unit of time T1/2 = 0.693/  = 0.693/ T1/2 Physical Properties of a Radioactive Material Half-life (T1/2) - The time taken for the number of atoms in a sample of an element to decay by half T1/2 Original Value Amount Left 1 100% 50% 2 50% 25% 3 25% 12.5% 4 12.5% 6.25% 5 6.25% 3.125% Physical Properties of a Radioactive Material Effective Half-life - The time required for the body to eliminate one half of the dose of any radioactive substance. 1/TE = 1/TP + 1/TB Where: TP= physical half-life TB= biological half-life Physical Properties of a Radioactive Material Activity (A) - Indicates the number of radionuclides disintegrating per second (dps or s-1) - The S.I. unit is the becquerel (Bq) - Old unit is the curie (Ci) - - 1 Bq = 1 disintegration per second (dps) 1 Ci = 3.7 x 1010 Bq A Radioactive Decay where: N = N0 e -T N0 - the original number of nuclei present T - the elapsed time  - the radioactive decay constant N - the number of nuclei remaining after the decay time Activity remaining = Original activity (0.5)n Where: n= number of half-lives. Radioactive Decay The amount of activity “A” remaining after “n” half-lives is given by A 1 = Ao 2n where: A is the activity at time, T Ao is the initial activity n is the number of half-lives w/c has elapsed n = T / T1/2  Radionuclide Half-Life Technetium-99m 6 hours Iodine-123 13 hours Iodine-131 8 days Phosphorus-32 14.3 days Iridium-192 74 days Cobalt-60 5.27 years Caesium-137 30 years Carbon-14 5730 years Uranium-238 4.5 x 10^9 years Activity: Physical Properties On Monday at 8 am, 10 kBq of Tc-99m is present. How much will remain on Friday at 8 am? 12.5 MBq of I-131 is present at noon on Wednesday. How much will remain 2 weeks later? Activity: Physical Properties If a piece of petrified wood contains 25% of the 14C that a tree living today contains, how old is the petrified wood? How many half-lives are required before a quantity of radioactive material has decayed to less than 1% of its original value? Modes of Decay Alpha Decay - spontaneous emission of an alpha particle from the nucleus - typically occurs with heavy nuclides (A > 150) and is often followed by gamma and characteristic x-ray emission  4 2  ++ Relatively massive Relatively slow Emission of an -particle or 4He nucleus (2 neutrons, 2 protons) Examples of some alpha emitters: radium, radon, uranium, thorium  Beta Decay A. Beta-minus/ Negatron emission - particle released when the nucleus changes a neutron into a proton and a beta particle B. Beta-plus/ Positron emission - occurs with radionuclides that are “neutron poor” (i.e., low N/Z ratio)   − Beta radiation may travel several feet in air and is moderately penetrating; can penetrate human skin to the "germinal layer,“ body penetration 0.2 to 1.3 cm Example of some pure B- emitters: strontium-90, carbon-14, tritium, and sulfur-35. Example of some pure B+ emitters: astatine-77, bromine-83, Activity: Modes of Decay A given element with an atomic number of 88 had underwent alpha decay. What is the reason for this and what would be the daughter element? What would be the new mass and atomic number of the element bromine if it undergoes positron emission? Would the number of protons increase or decrease?  Electron Capture/ K-Capture - Alternative to positron decay for neutron-deficient radionuclides - Nucleus captures an orbital (usually K- or L-shell) electron Example: 50V+ e–→50Ti + n + characteristic x-ray  Isomeric Transition - Gamma rays are emitted as the daughter nucleus transitions from the excited state to a lower-energy state - Examples of some gamma emitters: iodine- 131, cesium-137, cobalt-60, radium-226, and technetium-99m.  Auger process is the removal of an electron by a characteristic ray during electron capture. Internal Conversion is the removal of an electron by a gamma ray during isomeric transition.  TYPE OF APPROX. RANGE IN RANGE IN ORIGIN RADIATION ENERGY AIR SOFT TISSUE PARTICULATE ALPHA PARTICLE 4-7 MeV 1-10 cm ≤0.1 mm Heavy radioactive nuclei BETA PARTICLE 0-7 MeV 0-10 m 0-2 cm Radioactive nuclei ELECTROMAGNETIC X-RAYS 0-25 MeV 0-100 m 0-30 cm Electron cloud GAMMA RAYS 0-5 MeV 0-100 m 0-30 cm Radioactive nuclei