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Radiation Biology: Cell Biology

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Radiation Biology: Cell Biology Agenda Radiologic Units: • Greys, Sieverts, Coulombs per kg, & What You Need to Becquerel's Know • Conventional Units TODD VAN AUKEN M.ED. RT (R)(MR) • Other Concepts (LET, Q-Factor, Effective Dose, NCRP Report # 116) • Crazy Happenings with Radiation Coulomb per kg or C/kg-Exposure (X) Erythema Dose • A Coulomb (C) is the basic unit of electric charge • Measurement of positive and negative particles created when radiation ionizes atoms in dry air (Radiation intensity in the air) • Unit of Exposure for X-rays and Gamma Rays (Restricted to Photons only) • Used for x-ray equipment calibration (X-ray tube output) • Conventional Unit: Roentgen (R) Air Kerma Gray (Gy)-Absorbed Dose (D) • Kinetic energy is transferred from the primary beam • Amount of energy per unit mass absorbed by an (photons) to the patient (e-) irradiated object • SI quantity that can be used to measure radiation • 1 joule (J) of energy absorbed concentration transferred to a point at the surface of a in 1 g of absorbing material patient’s or radiographer’s body • Absorption of energy may • The energy transfer is called the kinetic energy result in biological damage released in the material or kerma (air kerma) • As the Z# of the object • Dose Area Product (DAP)- sum total of Air Kerma increases the absorbed dose over the exposed area of the patient’s surface (entire increases amount of energy delivered to the patient) • Conventional Unit: RAD (Radiation Absorbed Dose) Linear Energy Transfer Linear Energy Transfer Low LET Low LET High LET High LET LET= Rate at which energy is released as Dependent upon mass and energy of a charged particle travels through matter radiation or particle Linear Energy Transfer Low LET High LET The higher the mass or the lower the energy, the higher the LET Sievert- Equivalent and Effective Dose Quality Factor or Weighting Factor (WR) • Dose: The amount of radiation Energy absorbed in the Type of Radiation Q Factor Gray Sieverts body X-Ray 1 1 1 • Various types of radiation/particles produce varying Gamma Ray 1 1 1 amounts of damage (LET) Beta Particles 1 1 1 • Developed to measure biologic response of tissue from exposure to different types of photon radiation and Thermal Neutrons 5 1 5 particles Fast Neutrons 10 1 10 Alpha Particles 20 1 20 • Unit employed on dosimetry reports Sievert = Product of the absorbed dose in Gy and • Conventional Unit: REM (Roentgen-Equivalent-Man) the quality factor (Q) or Weighting Factor (WR) Dose Equivalence (EqD) Effective Dose (EfD) To calculate dose equivalence, use the following formula: z Tissues in the body are not EqD = D x WR equally affected by ionizing radiation Example: What is the total exposure a patient would receive if he/she were exposed to the following doses of ionizing photon and particulate z This method is employed radiation: .5 Gy of x-rays, .1 Gy of fast neutrons, .05 of alpha to estimate the dose to particles? each individual organ EqD = D x Q z The effective dose (EfD) x-rays = .5 x 1 or .5 Sv will allow you to estimate fast neutrons = .1 x 10 or 1 Sv the dose to an organ that is located outside of a alpha particles = .05 x 20 or 1 Sv protective lead apron EqD = .5 + 1 + 1 or 2.5 Sv Effective Dose (EfD) Effective Dose (EfD) To calculate effective dose, use the following formula: EfD = WR x WT x absorbed dose Example: What would the total exposure to the breasts be if a patient were exposed to a total body dose of .5 Gy of x-rays? EfD = WR x WT x absorbed dose EfD = 1 x 0.05 x .5 EfD = .025 Sv or 25 mSv to the breasts Becquerel (Bq)- Radioactivity Review z Quantity of radioactive material/Number of (C/kg) radioactive atoms decaying per second (not the radiation emitted) z Primarily employed in Nuclear Medicine z Conventional Unit: Curie (Ci) NCRP Report #116 Types of Dosimeters: • ALARA and Risk-Benefit Balance when using diagnostic amounts of radiation • Occupational Exposure- annual effective dose limit is 50 mSv (5 rem) • Cumulative effective dose (CEfD) limit = Age (in years) x 10 mSv (1 rem) • General Public- annual effective dose limit for frequent exposure is 1 mSv (.1 rem) • General Public- annual effective dose limit for infrequent exposure is 5 mSv (.5 rem) Dosimeters are required if there is a possibility that a HCW • Equivalent dose limit for embryo or fetus for all gestation will receive more than 1/10 of the recommended dose limit is 5 mSv (.5 rem or 500 mrem) (DL) Film Badge: Photographic Emulsion: z Earliest type employed (1940s) z Contain metal filters z Can be worn up to 3 months which is the maximum allowable time z Can measure doses as low as .1 mGy z Disadvantages May be affected by heat and humidity Does not provide an immediate reading Cannot be reused Thermoluminescence Dosimeters or TLD: Thermoluminescence Dosimeters or TLD: z Contain Lithium Fluoride (LiF) rods, chips, disks or powder z Crystals store energy when exposed to ionizing radiation z During processing, the LiF crystals are heated z Light is emitted in proportion to radiation exposure z An electric signal is generated by a photomultiplier tube z Can be worn up to 3 months between readings z Advantages Reusable and not affected by heat and humidity Lithium Fluoride (LiF) Can measure doses as low as .05 mGy z Primary disadvantage is that it does not provide an immediate reading Optically Stimulated Luminescence or OSL: Optically Stimulated Luminescence or OSL: z Aluminum Oxide (Al2O3) is used as the radiation detector z Exposure to ionizing radiation causes some electrons to be moved out of their normal position z During processing, a laser causes these electrons to move back to their original position z Light is released that is in proportion to the radiation exposure z The light is directed toward a photodiode, which generates a signal denoting the individual’s level of exposure z Can be worn up to 3 months between readings Aluminum Oxide (Al2O3) z Primary advantage is that an OSL can measure doses as low as .01 mGy.
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