Ionizing Radiation: Biological Effects and Safety

Consequences of Ionization in Human Cells

• Ionizing radiation transfers energy, enough to remove or add an electron, creating an ion.
• This process releases electrons from atoms and molecules, generating ions that break covalent bonds.
• Ionization can affect DNA by inducing breaks, creating unstable atoms.
• Highly reactive free molecules (free radicals) are created, capable of producing poisonous substances.
• New biologic molecules detrimental to living cells are created.
• Cellular injury may manifest as abnormal function or loss of function.
• Most atoms return to their original state without damage.

Properties/Characteristics of X-Rays

• Invisible and have varying degrees of penetration in normal skin.
• X-rays travel in straight lines at the speed of light until interacting with atoms.
• They are not deflected by electric or magnetic fields and cannot be focused with a lens.
• When passing through matter produce charged particles by interacting with atoms
• X-rays cause fluorescence in certain crystals and darken radiographic exposure.
• The degree of darkening corresponds to their intensity/quantity
• Heterogenous

Radiation Protection Goals

• Protect individuals from short and long-term radiation effects.
• Effects can occur in specific organs, organ systems, or the whole body, and impact future generations (cancer, genetic changes).
• ALARA (As Low As Reasonably Achievable) is a guiding principle.

Radiation Quantities and Units of Measure

• Exposure (C/kg): Measures ionization in air when ionizing radiation is present
• Ionization chambers quantify this, determining radiation output from x-ray equipment.
• Units: COULOMB PER KILOGRAM (MetricSI) or MILLIROENTGEN (subunit of roentgen).
• Absorbed Dose (mGy): Energy deposited in a material per unit mass.
• Higher energy deposition leads to more biomolecule disruption.
• Units: MILLIGRAY.
• Effective Dose (mSv): Measures biologic effects of ionizing radiation, estimating harm in humans.
• It considers the absorbed dose, radiation type, and organ/system irradiated.
• Units: MILLISIEVERT.

Justification for Imaging Procedures

• Weigh the benefits against the risks.
• Medical information gained from radiant energy exposure should outweigh the potential for biologic or genetic damage.

Maximizing Efficacy of Imaging Procedures

• Use minimal radiation exposure while still producing optimal images.
• Diagnostic efficacy is the degree to which the imaging study reveals the presence or absence of disease.

Principles of Radiation Protection

• Minimize Time exposed.
• Maximize Distance from source.
• Maximize Shielding.

Employer Requirements - Radiation Safety Program

• The Radiation Safety Officer (RSO) is responsible for ALARA program execution, enforcement, and maintenance in a hospital setting.
• ALARA is also known as Optimization for Radiation Protection (ORP)
• Employers must implement and maintain an effective radiation safety program by providing necessary resources.
• A written policy of ALARA program must be available to all employees.
• Perform routine exposure audits to find ways to lower radiation exposure in the workplace.

Radiation Worker Responsibilities

• Must be aware of the rules
• Perform duties consistent with ALARA.

Radiation Sensitivity - Children vs Adults

• Children are more radiosensitive, with about 3x greater risk. This is due to the presence of many still-reproducing cells.
• Early life radiation exposure can increase cancer risk in the 50s and 60s.
• Embryos exposed to radiation from atomic bombs in Hiroshima showed significantly increased fatal adulthood cancer.

Explaining Radiation Risk - Patients

• Answer patient questions using the BERT method (Background Equivalent Radiation Time).
• The BERT method compares radiation exposure to natural background radiation, emphasizing radiation as an innate environmental part.
• It is easy for the patient to comprehend

Image Gently & Image Wisely Campaigns

• Alliance for Radiation Safety in Pediatric Imaging: a partnership among medical societies to reduce radiation dose for pediatric patients.
• Image Gently: CT dose lowered using child-sized techniques (lower kV, mAs).
• Pediatric dose should be as reduced as much as 50% with no reduction in image quality
• Image Gently PLEDGE:
• Staff communication will make this a priority
• Protocol recommendations will be reviewed / adjustments will be made.
• Open communication with parents

Image Wisely

• This joint task force increases awareness about the increase in public exposure to ionizing radiation.
• It lowers radiation amounts in medically necessary studies and eliminating unnecessary procedures.

Pause & Pulse: Image Gently in Fluoroscopy Campaign

• Full understanding of fluoro devices on pediatric patients.
• Kids should be imaged with care - pause and adjust the technique.
• Child flouro procedures - pulse the radiation with the lowest possible pulse rate

Monitoring & Reporting Radiation Dose

• Required to log maximum skin dose as part of the patient record.
• Protocols for alert levels are engaged when the patient dose is predicted to, or has exceeded preset dose levels.
• Medical physicists estimate patient doses such as effective dose, peak skin dose, or fetal dose (prolonged fluoroscopy).
• The Joint Commission requires monitoring of patient dose in CT and IR.

Misc Radiation Facts

• Radiation was used medically for diagnosis starting in the 1900s.
• Radiation was implemented into healing arts in 1895.

Controlling Radiant Energy - Safely

• Use effective methods to limit or eliminate radiation-induced hazards.
• Knowledge of radiation-induced hazards gained over the years should be used
• Use of effective communication is key

Types of Radiation Examples

• Natural and Manmade/Medical radiation.

Electromagnetic Spectrum

• Electric and magnetic fields fluctuate rapidly as they travel through space
• EM waves are characterized by wavelength.
• All electromagnetic radiation has one common characteristic: Velocity
• Frequency, measured in hertz (Hz) cycles/second, and wavelength, measured in meters.
• Energy is the measurement of electron volts (eV).
• Electron volt is kinetic energy an electron gains moving through a 1 V potential difference.

Ionizing vs Non-Ionizing Radiation

• Ionizing: X-rays, Gamma Rays & UV Radiation >10 eV
• Non-ionizing: Radio Waves, Microwaves, Visible Light
• Non-ionizing radiation does not have sufficient kinetic energy to eject electrons from the atom

Particulate Radiations - Ionizing

• Radioactive Decay releases spontaneous nuclear emissions to relieve unstable nuclei.
• Radioactivity is the emission of ionizing radiation from nuclear decay
• Particulate Radiation is the product of radioactive decay
• Subatomic particles are ejected from the nucleus of atoms at high speeds
• Alpha Particles: two protons & two neutrons; occur in heavy elements like Uranium & Plutonium.
• Beta Particles: (beta decay) are identical Besides a small increase in ionizing power, beta particles are identical to high-speed electrons.
• Neutrons: uncharged particles that collide with nuclei.
• Protons: charged particles with enough kinetic energy to cause ionization by direct atomic collision. However, no ionization occurs when at rest.
• Alpha Decay (α-Decay): atomic nucleus emits an alpha particle (two protons, two neutrons).
• Occurs in heavier elements (Uranium & Plutonium). The nucleus becomes a new, smaller nucleus (daughter nucleus).
• Alpha decay allows unstable atoms to become stable when the strong nuclear force cannot hold the nucleus together.
• Hazardous when emitted in the body (internal hazard). Causes significant localized damage due to their short range.
• Alpha particles carry most of the energy lost alpha particle carries away most of the energy lost by the nucleus during decay.
• Alpha's are the least penetrating, possesses low penetrating power. Can be stopped by a piece of paper, mostly harmless externally.
• Beta Decay: occurs when a nucleus relieves instability by converting a neutron into a proton and an energetic electron (beta particle)
• Beta Electrons or Positrons (positively charged electron) are ejected from a neutron during decay.
• Neutrinos are emitted.
• Beta particles are 8000x lighter than alpha particles and penetrate more with less ionization along their path.
• Beta radiation has moderate penetration ability, more than Alpha and is used in Nuclear Medicine

Protons

• Protons interact strongly with negatively charged electrons in atoms due to positive charge.
• Less penetrating that high energy electrons
• Used in proton therapy

Neutrons

• They can knock out charged particles (protons) to ionize atoms when they collide with atomic nuclei, despite having no charge.
• Indirect ionizing radiation
• Penetrates more than Beta & Aplha
• Used in astrophysics & nuclear physics

Radiation Dose Units of Measure

• Absorbed Dose (D, radiation quantity): energy per unit mass absorbed in a material from ionizing radiation interaction.
• Measured in mGy or Gy
• Equivalent Dose (EqD): The equivalent is the measure of the dose from radiation.
• This overall value included the different degrees of tissue interaction
• Takes the type of ionizing radiation when absorbed into account (ex: proton, xray, etc)
• Measured in mSv.
• The EqD is used to calculate EfD

Effective Dose (EfD)

• The best estimate of overall harm from radiation on human tissue/organs.
• Takes body part irradiated and type of radiation into account.
• Measured in mSv.
• The ionizing radiation causes biologic damage by ejecting electrons from atoms.
• Atomic level radiation interaction results in molecular change and can cause cellular damage.
• Can result in ABNORMAL or COMPLETE LOSS OF CELL FUNCTION
• organic includes tissue or changes in blood count
• Excessive multicellular damage may exhibit genetic or somatic (body) changes:
  • Mutations (genetic)
  • Cataracts (somatic)
  • Leukemia (somatic)
• A body count average of 250mSv will cause a decrease in lymphocytes.

Three Sources of Natural Background Ionizing Radiation

• About 3.1 mSv:
  • Terrestrial Radiation .21 mSv: radioactive material in the earth's crust (Uranium, Radium & Thorium).
  • 2.3 mSv background radiation is from radon & thoron, emitting alpha particles.
    • Thoron is a radioactive decay product in an isotope of radon
  • Cosmic Radiation .3 mSv: radiation from sun (solar) and entire solar system, extraterrestrial origin
    • Greatest intensity located at higher altitudes because there is less atmospheric density that will allow for attenuation
    • Moderate intensity at sea level
    • Consists of primary energy protons
  • Internal Radiation .3 mSv: radioactive atoms (radionuclides) in small percentage of body's tissue.
    • Nuclides include potassium, carbon, hydrogen, and strontium.
    • The nuclides also create alpha, beta, and gamma radiation
  • 0.1mSv Human-Made Radiation:
    • Consumer Products containing radioactive materials.
      • Smoke detectors
      • Airport surveillance systems
      • Electron microscopes
      • Industrial static eliminators
    • Nuclear fuel for generation of power
    • Air travel
      • Increases contact and elevation with extraterrestrial radiation (cosmic rays).
      • Commercial flights- EqD rate of 0.005 – 0.01 mSv per flight-hour
      • Sun spots can increase the electromagnetic field and may eject space particles.
      • A 10- hour flight with sunspots can equal one CXR exam.

Sources of Human-Made Ionizing Radiation

• Include Medical (2.33 mSv) x-ray: .2 mSv, Nuc Med: .4 mSv, CT: 1.5 mSv, IR: .2 mSv
• Overall human total (human medical) equals 2.4mSv

Modalities Used in Medical Imaging

• Causing an increase in Pt doses since 1980 include: CT (63%), Nuc Med (15%), Radiography and Flouro and IR
• The amount of radiation may be defined by
  • Entrance skin exposure to skin and the glandular dose
  • Bone Marrow dose
  • Gonadal
  • Fetal (in pregnant women)

Nuclear Power Plant Accidents

• Three mile island in 1979 caused a meltdown as well as additional radiation
• Prediction was no more than one instance of radiation from this occurrence
• Chernobyl in 1998 resulted in approx 5k instance of cancer being attributed to the incident
• More than 1M instance of radiation
• Fukishima Daiichi in 2011 resulted in a 2nd world devasting nuclear power plant

Peak Kilovoltage (kVp) & Milliampere-seconds (mAs)

• kVp is technical parameter that means peak kilovoltage. kVp dictates the highest energy level of photons located within the X-ray beam. High kVp = Quality/Penetrating Power.
  • Potential Difference = Energy of electrons inside the x-ray tube and the Electrical Voltage from the tube cathode to anode. A 100kVp = 100,000 eV
  • The Beam Energy means photon energy, and is equivalent to half the energy from the most energetic photon source. A 100 kVp beam means a 100keV containing photon with approximately 33keV. keV is energy of specific xrays/
• mAs means Milliamperage (electron tube current) x time in seconds. It means the x-ray is activated.
  • mAs implies the quantity/amount of radiation during exposure. It maintains how much radiation is directed to the Pt during exposure
• All Absorbed Dose in atoms of biologic matter should be kept to a minimum

Absorption and Biologic Tissue Processes

• Process #1 = Photoelectric Absorption (the matter is absorbed)
• Process #2 = indirect Transmission
• Process #3 = Direct Transmission (passes without interaction)

Absorption - Process

• With interaction to Electromagnetic energy, energy is transferred from the x-ray source to the patients own tissue
  • The amount of potential of patients damage can be measured by D which means absorbed dose.
  • More energy = more biologic damage. Absorption variations are necessary in organs for diagnostic reasons

Scatter Process

• With interaction of energy to Pt = only a surrender of partial energy is absorbed
• Original path is diverted at separate angle.
• Primary: original state of source
• Exit (aka Image Formation): Photons leave through the tissues and strikes the image receptor
• Attenuated = intensity is reduced by absorption and does not strike the image receptor
• Attenuation = a broad term used for decreasing primary beams from striking the image receptor

Effects of Attenuation on Radiographic Images

• Low attenuation implies a brighter image on detector image
• high attenuation requires greater radiation because the more will be absorbed

X-ray Photon Transmission

• Transmitted = Photons Strike the DR Direct Transmission = photons are not stopped by the material Indirect Transmission = photons still strike DR but is the result of scatter
• indirect trans is always present*

Interaction Probabilities/Determinations

• Photon energy density
• dependence on atomic number
• Electron density
• And physical density
• Absorption Probabilities depend on Energy and Atom, and undergoes MORE photoelectric absoption rather than tissue mass
• Less tissues = same photoelectric absorbtion
• Contrast is enhanced when higher tissues can absorb/reach IR
• Proabability Increases with atomic/incident energy

Radiation/Energy Interaction

• Coherent scattering
• elastic, classic scattering
• no energy loss/small change in direction/fog result
• energy transfer by causing momentaray vibrates
• Absorption results in adequate contrast
• X-rays photon surrenders to atom that causes vacancy
• energy is released as xray but can cause further imbalance
• The energy equals differences that creates a characteristic xray/radition
• energy absorbed as photoelectric

Inner Shell Interaction

• the release of another electron causes a chain of absorption to an atomized state
• this excitation can occur again until equilibrium

Fluorescent Yield # characteristic xrays emitted

• a ratio of light emitting photons from DR, linked to atom
• Increased atom = increased yield when it comes to atomic number/ flourecence
• causes Auger effects; the emission and release by binding
• radiation-less effect; doesnt include further radiation
• reduces further charactertistic radiation

Compton Scattering

• modified, inelastic state
• Outer electron surrenders energy and has high potential for scattering during procedures
• xray photon energy releases outer electron that leads to collision
• leads to new direction that absorbs or releases electron

Pair Production

• incident xray passes 1.022 that creates the annhiliraiton
• position is used with nuc med pet scans

Photodisintigration

• happens wihtin energy and treated via therapeutic
• requires more radiation in the 10mV in level

Radiation Exposure + Body Structure

• causes instability the requires neuton
• if sufficient protons, then types of emissions occur
• Positive contrast leads to higher radiation doses
• radiation dose to organs cause body effects
• tissue is measured with EfD and requires tissue
• increases atomic interaction

Chapter #4: Early Acute Biologic Damage from X-Rays

• 1896: acute biologic damage
• Lesions and swelling on hands
• Blood disorders: anemia
• Leukemia-a 1904 radiation fatality called clarence dally

Radiation Repsonses (radiation damages by type)

• early effects hours and weeks in :Nausea, Fatigue, Fever,Desquamation
• tolerance is the measure of an adverse harmful response that requires low chance for sustaining damage and starting it
• Late tissue reactions (months and years): cataracts
• Fibrosis can cause stochastic effects of the body with can cause cancer genetic mutations
• radiation is quantified through air and air kerma through beam with can cause doses

Differentiation Quantites to Identify

• Exposure (X), SI with Air, radiation through space
• Air kerma in radiation to with quantities
• Absorbed dose is measure to actual receving or what to affect in a system with smaller units
• is the potential of effects that come to radiation, which is weighed from the impact, measures effects wiht the dose

Effective Dose Information

• EfD calculated for the total body through radiation
• takes in the radio sensitivtiy where weights effect