RADT 1020 - Radiation Protection

The X-ray Tube:

-In order to produce x-rays certain conditions must be present and include: -A source of electrons -A target material -High voltage -A vacuum -An X-ray tube is the device that allows all these conditions to exist.

X-ray Photons:

-X-ray photons are produced when the high-speed electrons from the cathode strike the anode target. -These electrons are traveling at half the speed of light -When they interact with the target they convert a tremendous amount of kinetic energy to the atoms of the target material. This interaction produces the x-ray photons and are termed target interactions

Beginning of Radiobiology:

-1895 - Wilhelm Conrad Roentgen discovered X-ray -1896 - Antoine Henri Becquerel observation of rays being given off by a uranium containing substance -1898 - Radium was discovered by Pierre and Marie Curie -Late 1800's - Elihu Thomson concluded that dermatitis on his fingers was a result of exposure to x-rays -1904 - Clarence Dally's (Thomas Edison assistant age 39)death with documentation of burns, serial amputations, and extensive lymph node involvement caused the medical community to seriously look at the effects of radiation exposure.

Bremsstrahlung Interactions:

-Bremsstrahlung interactions are named by the German word for braking or slowing. -Bremsstrahlung interactions may occur only when the incident electron interacts with the force field of the nucleus. -The incident electron must have enough energy to pass through the orbital shells and approach the nucleus of the atom. -When the incident electron gets close to the nucleus the nuclear force field is much to great for the electron to penetrate. This causes the electron to slow down (brake)and diverts the electron's course. -The electron loses energy when it changes direction and that energy that is lost during the braking is emitted as an x-ray photon. -These emissions are called bremsstrahlung photons and their energy is exactly the difference between the entering and exiting kinetic energy of the electron. -Within the diagnostic x-ray range most photons are produced by bremsstrahlung target interactions.

Characteristic Interactions:

-Characteristic interactions may occur only when the incident electron interacts with an inner-shell electron. -The incident electron must have enough energy to throw an inner-shell electron from its orbit, thus ionizing the atom. -The incident electron will continue but in a slightly different direction. -The "hole" that was created by the ejected inner-shell electron makes the atom unstable. -An electron from another shell will drop down to fill the "hole" -The dropping of an electron from an outer shell (higher energy state) into a lower shell (lower energy state) results in the energy difference between the two shells being emitted as an x-ray photon.

Radiation Protection History:

-During the 1950's researchers began to understand that radiation had an adverse effect on the human body and that steps needed to be taken to measure the levels of radiation. -Research since this time has guided Radiation Protection Protocols and set in place steps to protect both the public and personnel that work in the Radiologic Technology field.

Radiation Protection:

-From their research they formulated the Law of Bergonie and Tribondeau which states: -Stem or immature cells are more radiosensitive than mature cells -Younger tissues and organs are more radiosensitive than older tissues and organs -The higher the metabolic cell activity, the more radiosensitive it is. -The greater the proliferation and growth for tissues, the greater the radiosensitivity. -The results show that the fetus is the most radiosensitive compared to a child or adult. -Later in 1925 Paul Ancel and P. Vitemberger modified the law of Bergonie and Tribondeau. Their research concluded that there are two factors that affect the manifestation of radiation damage to a cell: -The amount of biologic stress the cell receives -Pre and Post- irradiation conditions to which the cell is exposed. -Both the Law of Bergonie/Tribondeau and the research done by Ancel and Vitemberger confirm that the radiosensitivity of cells is tied to the mitotic activity of the cell.

Interaction of X-radiation:

-Kv = highest energy level of photons in the x-ray beam. Peak kilovoltage controls the quality, or penetrating power of the x-ray beam. -mAs = the product of electron tube current and the amount of time in seconds that the x-ray tube is activated. mAs controls beam quantity. It is the main determinant of how much radiation is directed toward a patient during a selected x-ray exposure. -When X-rays interact with human tissue they may: -Interact with atoms of the biologic material in the patient -Pass through without interaction

Radiation Protection

-Radiation protection is defined as effective measures employed by radiation workers to safeguard patients, personnel, and the general public from unnecessary exposure to ionizing radiation. -Effective protective measures take into consideration both human and environmental physical determinants, technical elements, and procedural factors. -They consist of tools and techniques primarily designed to minimize radiation exposure while producing optimal-quality diagnostic images. -In 1906, Radiologist Jean Bergonie and Histologist Louis Tribondeau studied the effects of radiation by exposing rodent testicles to radiation. -They chose the testicles because they contain both mature (spermatozoa) and immature (spermatocytes) that have different functions and different rates of mitosis.

The x-ray Tube:

-The X-ray tube consists of -Cathode -Anode -Envelope -Protective housing

Scatter radiation:

-The attenuated beam includes both absorbed radiation and radiation that is scattered by interacting structures of the body. Each time a radiographic exposure is made millions of scatter events occur producing a blurring of the radiographic image. This undesirable exposure is called radiographic fog.

Cathode:

-The cathode is the negative side of the tube. -It functions to produce a thermionic cloud, conduct the high voltage to the gap between the anode and cathode and focus the electron stream. -The filament: -Is a small coiled wire made of thoriated tungsten. When heated the filament increases the movement of the electrons from the surface of the wire and ejects them a phenomenon described as boiling of electrons. This process is called thermionic emission.

The envelope:

-The entire cathode assembly and anode assembly (except for the stator that turns the anode) are located within the glass or metal envelope called the tube. -The point where the x-ray beam exits the tube is termed the window. -The primary function of the envelope is to maintain the vacuum between the anode and cathode. The removal of air permits the electrons to flow from cathode to anode without encountering the gas atoms of air

The Main Circuit:

-The main circuit modifies the incoming-line power to produce x-rays by boosting the voltage to the range that can produce x-rays and allows the radiographer to adjust the amperage, voltage, and length of exposure. -The Radiographer can adjust these functions on the control panel -The exposure switch controls the current to flow through the circuit -The timer circuit ends the exposure at the correct time set.

The Anode:

-The target area is the portion of the anode where the high voltage electrons impact. -It can be termed the target, focal spot, or focal track. -The actual focal spot is the physical area of the focal track that is impacted. -The effective focal spot is the area of the focal spot that is projected out of the tube toward the object being radiographed.

Target Interactions:

-The target interactions that produce x-ray photons consist of less than 1% of the total kinetic energy of the incident electrons. -Over 99% of the kinetic energy of the incident electrons is converted to heat. -There are two types of target interactions that can produce diagnostic-range x-ray photons. -Bremsstrahlung interactions -Characteristic interactions -The interaction that will occur depends on the electron kinetic energy and the binding energy of the electron shells.

Sources of Radiation:

-There are two sources of ionizing radiation: -Natural -Radon - gaseous radionuclide -Cosmic - from sun (solar) and beyond solar system (galactic) -Terrestrial - from radioactive material in the crust of the earth -Internal - radionuclides that make up a small percentage of the body's tissue -Manmade (artificial) -Medical Procedures -Consumer products -Nuclear fuel -Nuclear power

Anode:

-There are two types of anodes, a stationary and rotating. Rotating anodes have been in use since 1936. -The anode functions as the source of x-ray photons -It is made of molybdenum with a rhenium-alloyed tungsten as the target focal track material -The primary reasons for using tungsten are: -High atomic number -High melting point -Heat-conducting ability

Characteristic Interactions:

-These interactions are called characteristic photons because their energy is exactly the difference between the binding energy of the outer and inner shells between which the electron dropped -After an outer shell electron has dropped in to fill the "hole" another electron will drop to fill the "hole" it left, thus creating a characteristic cascade which can produce numerous x-ray photons for each electron that leaves the atom. -To produce an x-ray photon only electron drops into the K-shell will produce characteristic photons in the diagnostic x-ray range. -Characteristic drops from the other shells (L,M,N) have energies that are too low to be in the diagnostic radiology range. -Characteristic photons will not comprise any of the useful x-ray beam until the kVp is above 70. This is because a K-shell electron from tungsten cannot be removed without at least 69.5 KeV. -Between 80-100 kVp about 80-90% of the primary beam is produced by Bremsstrahlung interactions. 10-20% are produced by characteristic interactions.

Cardinal Rules of Radiation Protection:

-Time: Reduce the amount of the x-ray "beam-on" time. -Distance: Use as much distance as warranted between the x-ray tube and the patient for the exam. -Shielding: Always shield the patient with appropriate gonadal and/or specific area shielding devices. -OCCUPATIONAL EXPOSURE: -Shorten the length of time spent in a room where radiation is produced -Stand at the greatest distance possible from the x-ray beam -Place shielding between the radiographer and the source of radiation. (Lead apron)

Radiation Safety Officer (RSO):

-To have a successful ALARA program the facility must have a Radiation Safety Officer (RSO) that is responsible for: -Execution of the ALARA program -Enforcement of the ALARA program -Maintenance of the ALARA program -RSO is responsible to educate the radiation workers and ensure that all aspects of the ALARA principles are maintained

Direct and Indirect Transmission:

-When an x-ray beam passes through a patient it goes through a process called attenuation. Attenuation is the reduction in the number of primary photons in the x-ray beam through absorption (a total loss of radiation energy) and scatter (a change in direction of the beam resulting in a partial loss of energy) -Primary photons that pass directly through the patient without interacting is referred to as direct transmission. These non-interacting photons reach the image receptor to form the radiographic image. -Photons that are scattered or deflected with a potential loss of energy but still travel through the patient and strike the Image Receptor are referred to as Indirect Transmission. -Indirect Transmission degrades the radiographic image resulting in a loss of recorded detail. -The use of air gap techniques and radiographic grids can be effective in reducing indirect transmission.

Filament /Cathode:

-When the high voltage is released at exposure the thermionic cloud that surrounds the filament is driven toward the anode end of the tube where x-rays are produced. -The cathode end also contains a focusing cup that is designed to provide a low negative potential which forces the electrons to be focused into a narrow beam as it heads for the anode.

ALARA / ORP:

ALARA = As low as reasonably achievable, the ALARA principle should be a main part of every health care facility's personnel radiation control program. ORP = Optimization for Radiation Protection