Radiobiology Revision Q2 PDF

Lecture 5 ➔ Late Effects of Radiation Biological effects that manifest long after exposure to radiation. Can be categorized into deterministic and stochastic effects. ➔ LD 50/30 and LD 50/60 LD 50/30: Lethal dose for 50% of a population within 30 days (250–450 rad). LD 50/60: Lethal dose for 5...

Lecture 5 ➔ Late Effects of Radiation Biological effects that manifest long after exposure to radiation. Can be categorized into deterministic and stochastic effects. ➔ LD 50/30 and LD 50/60 LD 50/30: Lethal dose for 50% of a population within 30 days (250–450 rad). LD 50/60: Lethal dose for 50% within 60 days (250–300 rad). ➔ Deterministic Effects (Predictable Outcomes) - Definition: Effects that are predictable and occur only when radiation reaches a certain threshold. - Threshold Dose: The minimum amount of radiation required to damage specific tissues. Examples of Deterministic Effects: (cell death) ○ Eye: Cataract formation. ○ Skin: Reddening (erythema), hair loss, scarring (necrosis). ○ Reproductive Organs: Potential infertility. ○ Whole-Body: Only occurs at very high doses, which can lead to systemic failure in cases such as bone marrow damage, blood cell production reduction, gastrointestinal damage, and central nervous system damage. a. Less than 250 = no effects b. 250 - 1000 mSv = reduced RBC & platelets c. 1000 - 3000mSv = ARS - Delayed Onset: Unlike immediate effects like sunburn, deterministic effects may take weeks or years to appear after exposure. - The effect will not be seen at the time of exposure and when it occurs → the correlation to the radiation exposure may not be easily determined ➔ Stochastic Effects (Randomly Occurring) - Definition: Effects with NO threshold, including cancer and genetic mutations. Types: 1. Somatic Effects: These affect the individual exposed and can include cancers, sterility, and life-shortening. 2. Genetic Effects: Mutations in germ cells that may result in birth defects in offspring. ➔ Cancer Induction Mechanism: Radiation can cause mutations that may lead to cancer. Latency Period: ○ Leukemia: Shortest latency (5–15 years). ○ Solid Tumors: Longer latency. e.g., breast, lung, thyroid. (10–60 years). ➔ Fetal Radiation Sensitivity Development Stages: 1. Pre-implantation (up to day 9): High risk of spontaneous abortion (5–10 rad). 2. Organogenesis (2–8 weeks): Increased risk of congenital abnormalities. 3. Fetal Growth (post day 45): Risks to nervous system, behavior changes, reduced IQ, cancer. ➔ Risk Levels by Trimester: ○ Highest Risk: Organogenesis (weeks 2–8). ○ Moderate Risk: 2nd trimester. ○ Lowest Risk: 3rd trimester.  Lecture 6 ➔ Biological Effects Factors: Dose: The amount of radiation absorbed by the body. Dose Rate: Time over which the dose is received. 1. Acute exposure: Received over seconds or minutes. 2. Chronic exposure: Accumulated over days or years. Type of Radiation: alpha, beta, gamma impact different body areas. Organ Sensitivity: Certain organs (like eyes) are MORE sensitive than others (e.g., hands). Irradiated Area: Location of exposure matters—localized, extremities, full-body, or deep tissue. Radiation Source: Can be external (outside body) or internal (incorporated into tissues). External Radiation Effects: - High exposure can cause skin reddening (erythema), swelling (edema), hair loss (epilation), and cataracts. Internal Radiation Effects: Caused by ingested or inhaled radioactive materials. More hazardous due to constant exposure within the body. ➔ Classification of Radiation Damage Types of Effects: 1. Somatic Effects: Impact the individual exposed. 2. Genetic Effects: Affect the offspring of the exposed individual. 3. Stochastic Effects: Randomly occur, but probability increases with dose. 4. Non-Stochastic Effects: Occur only if dose exceeds a certain threshold. ➔ Exposure Types: 1.Acute Exposure: LARGE dose in a short period; symptoms show soon after exposure. 2. Chronic Exposure: LOW doses over extended periods; effects may appear after a latent period. ➔ Biological Damage Levels: Damage can occur at various levels: sub-cellular, cellular, organ, and organism level. Visible effects appear when millions of cells are affected. ➔ Categories of Biological Effects: Acute Somatic Effects: Immediate effects on the exposed individual. Delayed Somatic Effects: Appear years later. Genetic Effects: Appear in offspring. ❖ Acute Somatic Effects by Radiation Dose Dose range (mSv) Effects < 250 mSv No detectable effects 250 - 1,000 mSv Reduced blood cell count (both red and white) 1,000 - 3,000 mSv Nausea, vomiting, higher susceptibility to infections 3,000 - 6,000 mSv Severe symptoms including diarrhea, hemorrhage, sterility; 4,500 mSv causes 50% mortality within 30 days >6,000 mSv Symptoms intensify, CNS impairment; death within 30 days ➔ Effects of Irradiation on Humans Observed Effects: Effects typically seen after large doses, though even small doses are assumed to carry some risk.  High Cancer Sensitivity Organs: Includes breast, bladder, ovary, bone marrow, and blood. Moderate Cancer Sensitivity Organs: Includes lung, liver, kidney, thyroid, prostate, cervix, and skin. Low Cancer Sensitivity Organs: Includes brain. Notable Cancer Studies - radiation effects include atomic bomb survivors, radiation accident victims, and medical patients exposed to radiation. Common Sources of Cancer Data: - Atomic bomb survivors, low-level occupational exposures, and patients undergoing radiation treatment have provided valuable data on cancer risk. ➔ High-Risk Populations for Radiation Effects American radiologists: Increased leukemia and reduced life spans. Atomic bomb survivors: Malignant diseases and acute lethality. Radiation accident victims: Increased thyroid cancer and other malignancies. Uranium miners: Lung cancer due to radon exposure. Lecture 7 1. Regulatory Agencies Overview FANR (Federal Authority for Nuclear Regulation) ○ UAE’s main regulator for nuclear activities, based on 2008 policy and 2009 law. ○ Manages licensing, inspection, and international agreements. NRC (Nuclear Regulatory Commission) ○ U.S. agency regulating by-products from reactors. ○ Ensures safety for radiation workers and the public.  Agreement States ○ States with NRC authorization to regulate local radioactive materials (like radium). ○ Issue licenses and manage use within state borders. FDA (Food and Drug Administration) ○ Regulates human-use drugs, especially those involving radiation (like radiopharmaceuticals). DOT (Department of Transportation) ○ Sets rules for packaging and moving radioactive materials safely. 2. Radiation Safety Committees and Officers Radiation Safety Committee (RSC) ○ Creates and maintains a radiation safety program. ○ Ensures safety for patients and staff exposed to radiation. Radiation Safety Officer (RSO) ○ A trained specialist (often a physicist) in charge of facility radiation safety. ○ Develops safety protocols to protect everyone from radiation risks. ALARA Program (As Low As Reasonably Achievable) ○ A policy to keep radiation exposure as low as possible below set limits. 3. Radiation Exposure Limits and Survey Requirements Types of Surveys: ○ General Surveys – Regular checks to make sure all areas follow radiation rules. ○ Equipment Surveys – Checkups to confirm radiation equipment is safe to use. ○ Area Surveys – Daily checks in radiopharmaceutical areas and weekly in storage. Record-Keeping: ○ Keep survey records for 3 years.  Instrument Calibration and Checks: ○ Calibration – Before first use, annually, and after repairs. ○ Daily Checks – Source and battery check, no records needed. Dose Calibrator Tests: ○ Constancy Test: Daily. ○ Accuracy Test: Yearly and on setup. ○ Linearity Test: Every three months. ○ Geometry Test: When first installed. 4. Classification of Radiation Areas Unrestricted Areas ○ Radiation below 2 mR/hr; no access limits. Restricted Areas ○ Higher radiation levels; controlled access required. Controlled Areas ○ Outside restricted areas but access is sometimes limited. 5. Signage and Posting for Radiation Areas Radiation Symbol: ○ Purple or magenta blades on a yellow background. Types of Signs: ○ Caution: Radiation Area – Radiation above 5 mrem/hr but under 100 mrem/hr at 30 cm. ○ Caution: High Radiation Area – Radiation above 100 mR/hr at 30 cm. ○ Caution: Very High Radiation Area – Radiation above 500 rads/hr at 1 meter.  Lecture 8 ➔ Types of Radiation Units - Old Units: Roentgen (R), rad, rem, Curie (Ci). - SI Units: Coulomb per kilogram (C/kg), Gray (Gy), Sievert (Sv), Becquerel (Bq). ➔ Radiation Exposure 1. Roentgen (R): ○ Measures ionization in the air from gamma or x-rays. ○ 1 R = 2.58 x 10⁻⁴ C/kg (in air). ○ Does not show effects on the human body. 2. Exposure Rate: ○ Shows radiation over time. ○ Usually in C/kg per second or R/s (Roentgen per second). ○ Often noted per hour, like R/h (Roentgen per hour). ➔ Absorbed Dose (D) - Energy absorbed from radiation per unit mass. - Formula: D = Energy/ mass - Units: ○ Gray (Gy): SI unit for absorbed dose, 1 Gy = 1 J/kg. ○ rad: Older unit, where 1 Gy = 100 rad. Absorption: ○ Higher atomic number = MORE absorption. ○ Bones absorb more radiation than soft tissue. ➔ Equivalent Dose (H) - Absorbed dose adjusted for radiation type. - Formula: H= D × WR (weighting factor for radiation type). ○ w_R values: X-rays and gamma rays = 1. Alpha particles = 20. Neutrons = 5–20. Units: ○ Sievert (Sv): SI unit for equivalent dose.  ○ Rem: Older unit, 1 Sv = 100 rem. ➔ Effective Dose (E) - Adjusts for both radiation type and tissue sensitivity. - Formula: E = WT x HT ○ WT: Weighting factor for organ/tissue. ○ HT : Equivalent dose in organ/tissue. Units: ○ Sievert (Sv): SI unit. ○ Rem: Older unit, 1 Sv = 100 rem. Collective Effective Dose: Dose for a group of people exposed, calculated by multiplying effective dose by the population size. ➔ Radioactivity: decay rate of radioactive atoms. Units: ○ Becquerel (Bq): SI unit, 1 Bq = 1 disintegration per second. ○ Curie (Ci): Old unit, 1 Ci = 3.7 x 10¹⁰ Bq. Special Dosimetry in Medical Imaging ➔ CT Dose Index (CTDI) - Measures d=ose in CT scans. - Uses a pencil-shaped dosimeter placed in a phantom to measure direct beam and scatter radiation for one slice. ➔ Mammography Mean Glandular Dose (MGD) - Focuses on dose absorbed by glandular breast tissue. Calculation includes: ○ Incident exposure, ○ Half-value layer of the x-ray, ○ Breast thickness.