Chapter 9: Basic Radiation Protection and Radiobiology PDF

Chapter 9: Basic Radiation Protection and Radiobiology RA D R 1309: IN T R OD U C T ION T O RA D IOGRAP H Y & PAT I E N T CARE Objectives Identify the sources of ionizing radiation. List the units used to measure radiation exposure and their correct use. Describe the sources of radiation ex...

Chapter 9: Basic Radiation Protection and Radiobiology RA D R 1309: IN T R OD U C T ION T O RA D IOGRAP H Y & PAT I E N T CARE Objectives Identify the sources of ionizing radiation. List the units used to measure radiation exposure and their correct use. Describe the sources of radiation exposure. Explain the ways in which ionizing radiation interacts with matter. Objectives List the permissible limits of exposure for occupational exposure and the general public. Explain the reason for the varying sensitivity of human cells to ionizing radiation. Describe the ways in which the entire body responds to varying amounts of radiation. Discuss the various practices used to protect the patient from excessive radiation. Objectives Discuss the various approaches used to protect an occupational worker from excess radiation. Describe several devices used to detect and measure exposure to ionizing radiation. Define/explain all key terms listed within the chapter as stipulated in the examination objectives. Note: There has been material added in the PowerPoint slides that is not discussed in the course textbook. Students are responsible for knowledge of this information. Ionizing Radiation Ionizing radiation is energy capable of penetrating matter and possesses sufficient energy to eject orbital electrons along its path. This a risk for biologic changes within the body. The benefits of an imaging procedure should always outweigh the risk. It is the responsibility of the radiographer to protect all persons from unnecessary radiation at all times. Sources of Ionizing Radiation The two basic sources of ionizing radiation exposure are: Natural (or background) radiation: Cosmic radiation from the sun Naturally occurring radioactive substances present on the earth Human-made (artificial) radiation: Nuclear industry Radionuclides Medical and dental exposures (greatest source of human-made radiation) Consumer products Human-Made Radiation X-rays are a form of electromagnetic radiation that travels at the speed of light. They are bundles of energy moving as waves in space, depositing their energy randomly. For x-rays to be produced, three things must be present: A source of electrons A means to rapidly accelerate the electrons Something to rapidly stop this movement Rotating Anode Tube Human-Made Radiation The x-ray beam is heterogeneous, or having many energies. Measured in kiloelectron volts (keV). The primary or useful beam is directed towards the patient. Once the x-rays strike matter, three possibilities exist: They can be absorbed They can transfer some energy and then scatter They can pass through the unaffected  Interactions of X-Rays With Matter OC C U R IN T H E OC C U R I N T H E D IAG N OS T IC RA N GE T H E RA P E U T IC RA N GE 1. Classic Coherent Scattering 4. Pair Production 2. Photoelectric Interaction 5. Photodisintegration Directly influence patient and occupational worker exposure 3. Compton Scattering Directly influence patient and occupational worker exposure Classic Coherent Scattering Interactions that involve x-ray photons with energy levels below 10 keV. Also known as coherent, Thomson, or unmodified scattering. Results in no energy transfer to the patient. Does not create ionization. Photoelectric Interaction Results in complete energy absorption. Responsible for producing secondary radiation within the patient, known as characteristic radiation. Constitutes the greatest hazard to patients in diagnostic radiography. Results in ionization of the atom. Compton Scattering It is responsible for a majority of occupational worker exposure to radiation. Also known as modified or Compton scattering. Results in ionization of the atom. Pair Production For this interaction to occur, x-ray photons must possess a minimum of 1.02 MeV of energy. Equipment used in diagnostic radiography cannot produce photons that possess this energy. These interactions are of particular importance in radiation therapy. Pair Production The incident x-ray photon does not interact with the electron orbits; instead, it interacts with the nucleus. The photon disappears and two particles replace it; a positron and a negatron. The positron (e+) is a positively charged particle and the negatron (e-) is negatively charged. Pair Production Each particle possesses half the energy (minimum, 0.51 MeV) of the original x- ray photon. The negatron will eventually lose it’s energy and combine with another atom. The positron is unstable, and it will interact with the first electron that it comes into contact with. Pair Production The interaction between the positron and electron is called the annihilation reaction, in which both particles are destroyed. The energy from the two particles is converted into 2 x-rays that will move in opposite directions. No energy is lost during this type of interaction; it is converted into pairs of particles or x-rays. Photodisintegration For this interaction to occur, photons with a minimum of 10 million electron volts (MeV) are required. It does not occur in diagnostic radiography, but does occur in the nuclear industry. Photodisintegration The x-ray photon interacts directly with the nucleus of an atom, which causes a state of excitement within the nucleus. The photon disappears, followed by the emission of a nuclear fragment. Units of Measure 1920’s: A system of units was developed to quantify the amount of radiation a patient or occupational worker receives. 1948: International Committee for Weights and Measures developed a system of units based on the metric system. 1985: The International System {SI} of Units was officially adopted. Units of Measure Exposure (X) is the measure of ionization in air as a result of exposure to x-rays or gamma rays: Traditional unit: Roentgen (R) SI unit: Coulomb per kilogram (C/kg) Air kerma (kinetic energy released in matter) is the kinetic energy transferred from a beam of radiation to air or tissue in matter: Air kerma will replace the unit exposure SI unit: Gray (Gy) Units of Measure Absorbed dose (D) is the measure of radiation absorbed in object, such as the human body: Traditional unit: Radiation absorbed dose (rad) SI unit: Gray (Gy), Gya and Gyt refers to radiation dose in air or tissue Units of Measure Effective dose (EfD) and dose equivalent (EqD) are used to measure occupational exposure: Traditional unit: Radiation equivalent man (rem) SI unit: Sievert (Sv) Sv = Absorbed dose (Gy) x quality factor (Q) The quality factor indicates how harmful the radiation is on a scale from 1-20. The larger the number, the more harmful the radiation. Gy x Q is a formula used to determine occupational exposure in SI Units Units of Measure Radioactivity is the measure of the rate that a radionuclide decays: Traditional unit: Curie (Ci) SI unit: Becquerel (Bq) Defined as 1 disintegration per second (d/s), or 1 d/s = 1 Bq Table 9.1 Correction needed under Absorbed Dose in the textbook: Under the quantity section of the table for Absorbed dose (D), remove the (EfD) Quantity Traditional Unit SI Unit Exposure (X) Roentgen (R) Coulomb per kilogram (C/kg) Air Kerma Gray (Gy) Absorbed Dose (D) Rad Gray (Gy) Effective Dose (EfD) Rem Sievert (Sv) Dose Equivalent (EqD) Rem Sievert (Sv) Radioactivity Curie (Ci) Becquerel (Bq) Standards for Regulation of Exposure C D R H (C E N T E R F OR N C R P ( N AT I ON A L C OU N C IL D E VIC E S AN D OF RAD I AT I ON P R OT E C T ION RAD IOLOGIC AL H E ALT H ): A N D M E AS U R E M E N T S ): Collects and distributes Sets and regulates the information regarding standards for radiation- radiation awareness and safe practice to the public. producing equipment. Considered an advisory group; Continues to research does not have the authority to enforce the recommendations. possible ways of Established effective dose minimizing exposure to limits that take into account ionizing radiation. various types of radiation exposure and tissue sensitivities. Standards for Regulation of Exposure N RC (N U C L E AR E F F E C T I VE D OS E L IM IT R E GUL ATORY C OM M IS S ION ): R E C OM M E N DAT ION S It is responsible for enforcing The NCRP cooperates with radiation regulations. other organizations to review the latest data on radiation measurements and protection. Effective dose limit recommendations have been set to minimize the biologic risk to exposed persons. Effective Dose Limits The annual whole-body effective dose limit for occupational personnel is 50 mSv. Maximum cumulative whole-body dose limit is 10 mSv × age. Whole-body dose equivalent limit is 5 mSv (0.5 rem) for the general population, which represents 1/10 of the occupational worker’s limit. Standards for Regulation of Exposure Nonthreshold and threshold Nonthreshold indicates that no dose exists below which the risk of damage does not exist. Threshold indicates there is a safe dose that will not result in the possibility of damage. Risk versus benefit Benefits of exam must outweigh the potential risks from radiation exposure. ALARA As Low As Reasonably Achievable Biologic Response to Ionizing Radiation Ionizing radiation, absorbed by matter, undergoes energy conversions that result in changes in anatomic structure. These changes, when considered in light of living tissue, can have major consequences on the life of any organism. Basic Cell Structure Cells have two major parts Nucleus Cytoplasm Genetic material of a cell is contained in nucleus 80% of cell content is water Two classes of human cells Somatic Germ  Theories for Cellular Absorption of Ionizing Radiation D IR E C T H IT T H E ORY IN D IR E C T H IT T H E ORY When DNA is hit by ionizing Key molecules are affected by radiation, breaks in the radiation depositing its energy bases or phosphate bonds elsewhere in the cell. can result in rearrangement For example, because cells are or loss of genetic approximately 80% water, information, which can injure indirect action occurs when or kill the cell as it continues water molecules are ionized. through its life cycle. This action produces chemical changes within the cell that alter the internal environment, injuring the cell, which can result in eventual cell death. Note: With x-radiation and gamma radiation, the vast majority of cellular damage is the result of indirect hits. Target Theory of Absorption of Ionizing Radiation Both direct and indirect interactions with ionizing radiation apply to this theory. This theory states that if damage occurs to a molecule that is in abundant supply, the effect to the cell may not be as detrimental because others exist to maintain the function of the cell. Injury to a molecule that is in limited supply, however, can be life-threatening, because no immediate replacement is available. Radiosensitivity of Cells B E R GON IE A N D A N C E L AN D V IT E M B E R GE R T R IBON D E A U Cells are most radiosensitive Cells possess the same to radiation during active sensitivity to radiation; the division, when they are time of expression of injury is primitive in structure and the factor that differs. function. Rapidly dividing cells Cells resistant to radiation, demonstrate the injury are more specialized in sooner and only appear as structure and function and though they are more do not undergo repeated sensitive to radiation than mitosis. those whose mitotic rate is slower. Response of Cells to Radiation R E S ULT S OF RA D IAT ION T O F U N C T I ON S OF C E L L A CELL S U RV IVA L T O RA D IAT ION Cell death Cell radiosensitivity Delayed mitosis Type of damage Altered mitotic rate Type of radiation Cells also try to repair Radiation exposure rate damage that may be Total dose of radiation given sustained Fortunately, most cells can recover from radiation damage. Note: Incomplete repair can result in adverse biologic effects.  Total Body Response to Radiation Acute Radiation Syndrome (ARS) occurs only when the organism is exposed fully (total body) to an external source of radiation given in a few minutes. Early Effects of Radiation Exposure Prodromal stage Latent period Manifest stage There are 3 Radiation Syndromes 1. Bone marrow, or hematopoietic, syndrome 2. Gastrointestinal (GI) syndrome 3. Central nervous system (CNS) syndrome Table 9.3 Bone Marrow Gastrointestinal Central Nervous (Hematopoietic) (GI) Syndrome System (CNS) Syndrome Syndrome Dose required 2-10 Gy 10-50 Gy 50+ Gy 200-1000 rad 1000-5000 rad 5000+ rad Manifest Infection, Massive diarrhea, Seizures, coma, symptoms hemorrhage, nausea, vomiting, eventual death anemia fever Causes of Inability to Damage to Brain edema, symptoms produce blood epithelial lining of intracranial cells in the bone the GI system pressure, CNS marrow failure Mean Survival* 6-8 weeks 3-10 days Few hours to 2-3 (or recovery in 6 days months)  Total Body Response to Radiation Late Effects of Radiation Exposure These effects can result not only from high doses of radiation, but also from low doses administered over a longer time. Somatic effects Develop in the individual exposed. The two most frequent effects are cataract formation and carcinogenesis. Genetic effects Occur in future generations as a result of damage to the germ cells. Mutations that result are recessive. They appear only if the mutated cell is fertilized by another reproductive cell carrying the same mutation.  Effects of Radiation Therapy Every person will react different to radiation therapy treatment. Side effects will depend on the type and location of cancer, the dose of radiation given, and the patient’s general health. Early side effects happen during or shortly after treatment and are typically short-term, mild, and treatable. Late side effects can take months or years to develop. Protecting the Patient Cardinal Rules of The use of patient Protection shielding is essential in o Time the practice of ALARA o Distance Shield types o Shielding o Flat contact shields o Shadow shields o Shaped, contour shields o Correction needed in textbook for description of Fig 9.7. The image is demonstrating types of gonadal protection. Additional Methods of Protection Beam Restriction Restrict the x-ray beam no larger than the area of interest. Image Receptor Speed Faster speed image receptors result in decreased exposure to the patient by responding to the radiation faster with the use of lower technical factors. Additional Methods of Protection Technical Factor Selection Kilovoltage controls the energy of the x-rays. Reduced kilovoltage results in higher x-ray absorption in the patient. Filtration Aluminum is added that serves to absorb the low energy x-rays that are produced in the x-ray tube. Low energy x-rays will enter the patient’s body, but will not have enough energy to exit. This would increase patient dose and contribute nothing to the final radiographic image. Protecting the Radiographic and Imaging Sciences Professional The same principles of time, distance, and shielding are used to reduce occupational worker’s exposure to radiation. Time Minimize the time spent in the room when ionizing radiation is being produced. Distance Use the greatest possible distance from the source of exposure. Shielding Place a shield between the worker and the radiation source. Distance Distance is the best and most effective method of protection for the radiographer. The inverse square law states that as distance from the x- ray beam increases, radiation exposure decreases. Correction needed in textbook for description of Fig 9.8. The image is demonstrating the inverse square law. Distance Inverse Square Law New intensity = Old distance2 Old intensity = New distance2 Doubling the distance of the source of radiation reduces the exposure by a factor of 4 and vice versa. Radiographers should not hold a patient during a procedure. Shielding Shielding includes lead impregnated aprons and gloves. Contain between 0.25 to 1.0 mm of lead equivalency. Fluoroscopic procedures require aprons with 0.5 mm lead. Shielding Primary radiation (useful Secondary radiation consists beam) is the radiation of x-rays scattered from the patient and other objects emitted directly from the such as imaging hardware x-ray tube that is used for and leakage radiation from patient imaging. the protective housing of the x-ray tube. A primary barrier is a wall, A secondary barrier is a wall, ceiling, floor or other ceiling, floor or other structures that will structures that will intercept intercept radiation and attenuate leakage and emitted directly from the scattered radiation emitted x-ray tube. from patient and other objects. Primary and Secondary Radiation and Barriers Table 9.4 Pregnant Student Student pregnancy is covered under NRC regulations regarding the declared pregnant worker. Should a pregnant student voluntarily disclose her pregnancy in writing to her program officials, a second monitor (fetal dosimetry badge) is issued for all energized laboratory sessions and clinical assignments. Declaration of pregnancy is required in order for the educational program to order the fetal monitor. Dose limits for the embryo-fetus. Radiation Monitoring Any occupational worker who is regularly exposed to ionizing radiation must be monitored to determine estimated exposure. Any worker who is likely to receive more than one tenth of the recommended dose-equivalent limit should be monitored. Three most common personnel monitoring dosimeters: Optically Stimulated Luminescence Dosimeter (OSL) Thermoluminescent Dosimeter (TLD) Pocket Dosimeter, or Pocket Direct Ion Storage (DIS) Dosimeter  Radiation Monitoring OSL TLD DIS Correction needed in textbook for description of Fig 9.9. The image is demonstrating an OSL. Table 9.5 Optically Stimulated Thermoluminescent Luminescence Dosimeters Dosimeters Construction Plastic holder containing Plastic holder containing sensing material, tin and crystals of sensing copper filters, and an material open window Sensing material Strip of aluminum oxide Lithium fluoride crystals crystals Processing Crystals are heated; Crystals are heated; light omitted is light emitted is proportional to the dose proportional to the dose received. The dosimeter received. The dosimeter cannot provide cannot provide immediate readings of immediate readings of exposure. exposure. Addition to Table 9.5 Direct Ion Storage Dosimeters Construction Small ionization gas filled dosimeter Sensing material Connected to a “solid state” device with electrically programmable read-only memory (EEPROM) Processing When radiation ionizes the gas in the ionization chamber, the cumulative electric charge is stored in the EEPROM and will remain in the device until “read out”. It can be read out through a USB and provide instant access to data.  Radiation Monitoring OSL TLD DIS Correction needed in textbook for description of Fig 9.9. The image is demonstrating an OSL. Radiation Monitoring Monitors measure the quantity of radiation received on the basis of conditions in which the radiographer was placed. Exposure data are collected for a specified period of time. Worn at the collar level and outside of a lead apron. Device should always face forward. Pregnant radiographers may have a second device worn at waist level and under the lead apron. Radiation Monitoring Field survey devices measure the presence and rate of radiation. Known as field survey instruments. Geiger-Muller counter Summary X-radiation has the potential to create ionizations in human tissue. Ionizations can be harmful and cause cell disturbances and genetic alterations. Effects may be early or late and are dose dependent. Use the Cardinal Rules of protection. Radiographers have a professional responsibility to consistently practice ALARA.