Radiopharmaceuticals Unit-5 PDF

# Radiopharmaceuticals & Contrast Media ## Radiopharmaceuticals - Radioactive compounds - Pharmaceutical formulation ### Property of - Emitting rays of particles & decomposes. - Time & become unstable ### Definition - Radiopharmaceuticals are group of formulations which contains radioactive m...

# Radiopharmaceuticals & Contrast Media ## Radiopharmaceuticals - Radioactive compounds - Pharmaceutical formulation ### Property of - Emitting rays of particles & decomposes. - Time & become unstable ### Definition - Radiopharmaceuticals are group of formulations which contains radioactive materials. ### Use - Diagnostic Purpose - Therapeutic agents ### Note - Atomic Number: Number of protons in nucleus. - Atomic Mass: Number of protons + Number of neutrons. ## Isotopes - The elements have same number of protons but a different number of neutrons. - Example: - C₁₂: 6 protons, 6 neutrons - C₁₃: 6 protons, 7 neutrons - C₁₄: 6 protons, 8 neutrons ## Radioisotopes (Radionuclides) - Unstable form of a chemical element that releases radiation as it breaks down & becomes more stable. - Naturally: Ra-226, Co-60, Carbon-14 - Artificially: Nuclear reactor, cyclotron ## Nature of Radiation - Alpha rays - Beta rays - Gamma rays ### Affect the photographic plate #### Alpha rays - Low penetrating power - Carry a positive charge & detected by a magnetic field. - 2 positive charges & 4 AMU (Atomic mass unit). - Attracted in a negative electric field #### Beta Rays - Unit negative charge - Negligible mass emitted by nucleus. - Energy & velocity very high. - High penetration compared to x-particles (rays). - Attracted by (+) charge. - Can penetrate tissues. - Moderate ionizing power. - High kinetic energy electrons. #### Gamma rays - Same character as high frequency electromagnetic rays - More penetrating power compared to α & β - No mass & no charge. - Poor ionizing power & same velocity as light. ## Radiation Absorbed Dose (RAD) - Unit of radioactivity - RBE (Relative Biological Effectiveness) ### Curie [Ci/c] - It is defined as the quantity of radioactive substance. Undergo 3.7x10¹⁰ disintegration/second. - This is equal to about 1 gm radium. Undergo 3.7x10¹⁰ disintegration/second. ### Subunits - Millicurie (mc) - 1x10^-3 of curie. It undergo's 3.7x10⁷ disintegration/second - Micro-curie (µc) - 1t Undergo 3.7x10⁴ disintegration/second. ## Roentgen - Unit of exposure 1 R= 2.58x10^-4 coulombs/kg of air ## Radioactivity decay rate (half life) - Disintegration rate of radioactivity. - It is defined as the time required for a radioactive substance to decay to one half of its original value at a given point of time. - Denotes by t_1/2 (half-life). It is the original value at a given time. - Every radioactive element has its own t_1/2 life. - t_1/2 = 0.693/λ - λ = Disintegration constant - Unit = sec^-1 - Example: 64 microcuries radioactivity in a given sample of ferric citrate (⁵⁹Fe) solution, at a particular date: 13/01/2025. Calculate the radioactivity at a later date: 27/02/2025. - 64 µc (Fe⁵⁹) solution - After first half-life t_1/2= 45 days: 32 µc (Fe⁵⁹) solution - After second half-life t_1/2= 45 days: 16 µc (Fe⁵⁹) solution - After third half-life t_1/2= 45 days: 8 µc (Fe⁵⁹) solution - After 4th half-life t_1/2= 45 days: 4 µc (Fe⁵⁹) solution ## Harmful biological effects of radiation - **Bad & dangerous effect on biological systems** - Cause abnormalities like: - Genetic structure (DNA & RNA) changes - Irreversible changes - Number of living cells - Noticed after some time (hours, days, months) - Affect the next generation - **Cause creation of free radicals** - Example: H₂O + radical particle → H⁺ + OH^· (chain initiation) H₂O + H^· → H₂ + OH^· (chain propagation) H₂O + OH^· → H₂O₂ + H^· (continous until the last molecule) - H⁺ + H⁺ → H₂ (chain termination at last step) - OH^· + OH^· → H₂O₂ ## Measurement of radioactivity - Important for identification of α, β, γ rays. - Assay the radionuclide emitting radiation. - Identify basic properties. ### Ionization effect - Ionisation chamber - Proportional counter - Geiger-muller counter - Gas-filled detectors #### Ionization chamber - Simple gas-filled detector. - Principle: Charges created by direct ionization of gas through electric field. - Consist: - Chamber - Argon, Helium - 2 electrodes (50-100V) - Radiation bringing ionization of molecules - Emission which supply current. #### Radiation Source - Voltmeter - Condenser (capacitor) - Battery ### Advantages of using an ionization chamber - Good, uniform response to radiation over a wide range of energy. ### Disadvantages of using an ionization chamber - Relative weak out put, pulse (low signal) ### Proportional Counter - Modified ionization chamber. - High voltage operation (1000-2000V). - Filled gas - 90% Ar + 10% methane - Detect charged particle having low ionization power. ## Geiger-muller counter - Oldest radiation detector. - Easy to detect α, β, γ rays. - In 1928 by Geiger & muller - Detect & measure ionizing radiation. ### Principle - GM tube: Filled inert gas (Ar, Ne, He) - Sense elements: Detects the radiation - Applied voltage (450-500V) - Low pressure - Tube conducts the electrical charge - When photon incident radiation, it causes ionization. - Amplifies the ionization by capacitor. - Electronic result. ### Construction - Cylinder (1-2 cm diameter) - Made of stainless steel or glass-coated Ag - Tungsten wire, suspended at the end. - A glass head positively charged (wire). - He, Ne, Ar gases - 450 V - A negative charged electrode - Scale, rate meter (voltmeter) ### Working - Radiation enters via thin section window - Cause ionization of gases - Electron knocked out of the atom - It remains positively charged. ## Scintillation Detector - Incident on certain, sensitive substance. - High energy radiation/photon - Fluorescence (phosphorescence) emitted by substance. - High sensitivity - High scintillation efficiency - Used for measuring absorbed radiation. - In photomultiplier tube. - It multiplies the signal intensity. ### Working - Ionization tract: Photocathode, focusing electrode, photomultiplier tube, connector pins. - Scintillator: Primary electrons - Dynodes: Secondary electrons, computer - Dynodes contain loose bound electrons. - They multiply the signal efficiency continuously. - Phosphor or fluor compounds ## Handling and storage of radioactive materials - Isolated chambers and containment unit. - Away from exposure of human beings - α and β-emitters stored in glass (thick) - γ-emitters stored in lead containers - Exposure causes blood cancer. - Lead shielding required when a person is handling radioactive material. ### Labelling radioactive materials - Statement of radioactive (international symbol for radioactivity) - Appropriate preparation, diagnostic and therapeutic purpose. - Route of administration must be mentioned - Expiry date necessary on product. - Batch and Lot No. must be assigned by manufacturer. ## Applications of radiopharmaceuticals - **Treatment of cancer-tumors** - Americum-241 - Californium-252 - Cobalt-60 - Gold-194 - Holmium-166 - Liver - Liver tumours - **Thyroid disease** - Iodine-131 - Hyperthyroidism (Grave's disease) - Thyroid cancer - **Arthritis treatment** - Erbium-169: Relieves the pain in synovial joints. - Ammonia N-13: Diagnosis of coronary artery disease - Iodine-125: Evaluate kidney filtration rate.