Week 9
A stochastic effect: 1.Requires no threshold of radiation exposure for effect to occur 2.Requires a threshold of radiation exposure before any effect would occur A deterministic or non stochastic effect: 1.Requires no threshold of radiation exposure for effect to occur 2.Requires a threshold of radiation exposure before any effect would occur What is the threshold dose? 1.A dose level below which there is no effect of radiation 2.A linear dose response 3.Effects that occur by chance What is the MPD for a pregnant worker? 1.5,000 REM/year 2.50 REM/gestation period 3.5 REM/gestation period 4.0.5 REM/gestation period State the cumulative MPD for a 55 year old occupationally exposed man using the NEW formula 1.37 REM 2.185 REM 3.55 REM 4. 257 REM What does an "m" mean on a dosimeter report? 1.That the maximum exposure has been received for the month 2.That the minimum time passed between monitoring. 3.That the exposure received was so minimal that it did not record 4.That the maximum exposure has been received for the entire year Which of these is allowed a greater amount of weekly radiation exposure? 1.Controlled area 2.Uncontrolled area How often must film badges be sent in for processing? 1.Every month 2.Every 2 months 3.Every 3 months 4.Once a year
1. 2. 1. 4. 3. 3. 1. 1.
What does an "M" mean on a dosimeter report? 1.That the maximum exposure has been received for the month 2.That the minimum time passed between monitoring. 3.That the exposure received was so minimal that it did not record 4.That the maximum exposure has been received for the entire year How often must film badges be sent in for processing? 1.Every month 2.Every 2 months 3.Every 3 months 4. Once a year Which of these is allowed a greater amount of weekly radiation exposure? 1.Controlled area 2. Uncontrolled area What is the annual whole body MPD for occupationally exposed persons? 1.5,000 REM 2.500 REM 3.50 REM 4. 5 REM What is the MPD for a pregnant worker? 1.5,000 REM/yr 2.50 REM/gestation period 3.5 REM/gestation period 4..5 REM/gestation period State the cumulative MPD for a 55 year old occupationally exposed man using the NEW formula 1.37 REM 2.185 REM 3.55 REM 4. 257 REM Which of these is NOT a cardinal principle of radiation protection? 1.kVp 2.Time 3.Distance 4. Shielding
3. 1. 1. 4. 4. 3. 1.
Average Annual Dose of Radiation: Average annual total effective dose equivalent to the general population (nonsmokers) from naturally occurring and man-made sources = 360 mrem. Remember how radiation affects cells? •Direct - breaks DNA strand •Indirect - interacts with water molecule to liberate a free radical - damages DNA
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Background Radiation: As Earthlings....people are exposed to radiation from various sources every day It comes from: -Space - cosmic rays -The earth - from the rocks and soil - food -Ourselves - from radioactive carbon and potassium in our bodies -Radon Gas Some of this radiation comes from: -Man-Made Sources --Tobacco Products --Medical Procedures (X-rays, etc.) --Building Materials --Domestic Water --Other
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Biological Effects of Radiation: Broken into two groups according to: -How the responses (symptoms or effects) relate to dose -or amount of radiation received Stochastic Effects - light switch Deterministic (non-stochastic) Effects - bank account
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CUMULATIVE MPD (old formula): over the life of the radiation worker determined by: 5 (n-18) -n = age in years -5 is because that is the whole body REM/year -18 points out that no one under 18 should be working with ionizing radiation If they do, their MPD is considered that of the general population CUMULATIVE MPD (NEW FORMULA) 1 x age (of occupationally exposed individual)
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Cardinal Principles of Radiation Protection For the Radiographer: 1. TIME: as short as possible (not applicable for diagnostic radiography, we use a short exposure time to reduce motion blur on the image) 2. DISTANCE: as far as possible (inverse square law) - our SID's are already set for this. Distance is for the radiographer to stay as far from the beam as possible. Behind the protective barrier. 3. SHIELDING: dense, high atomic number -often lead bonded to sheet rock - primary barriers -4" of masonry is equivalent to 1/16" of lead - secondary barriers
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Collimation: Equipped with a light localized, variable-aperture collimator. Cone or diaphragms may be used in specialized machines. Collimation must be accurate to 2% of the SID. Positive Beam Limitation called PBL is automatic collimation to minimum film size -must be accurate within 2% Beam Alignment: -Each x-ray tube should have a mechanism to ensure that the tube is properly aligned to the image receptor. -It would do no good to align the light and beam if the film is not aligned.
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Control Panel: The control panel must indicate the conditions of the exposure and positively indicate when the tube is energized. Indications include: -Exposure Factors --mA, time or mAs --kVp --Focal Spot -A visible (meter needle moves or a light flashes) and audible (beep, bell, or chime) signal that the tube is being energized. Stops when exposure ends
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Control badge: Control badges are used to monitor background and transportation exposure to the entire batch of badges Exposure measured on control badge is deducted from the exposure of personnel badges Keep away from radiation area Send back to monitoring company with batch of badges
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Cosmic Source of Radiation: •Total average dose ~ 28 mrem/year •Comes from the sun and outer space - Consists of positively charged particles and gamma radiation •At sea level, average annual cosmic radiation dose - approx. 26 mrem. •Higher elevations? The amount of atmosphere shielding cosmic rays decreases -Dose increases •Astronauts, pilots, high altitude increases dose
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DESIGN OF PROTECTIVE BARRIERS: Hire a radiation physicist Many vendors help Room design must be approved by the state prior to installation When designing a radiographic room a number of factors must be addressed besides the architectural features. -Machine location -Range of movement of tube and tube direction -Use of adjoining rooms -Which floor you are on
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Designing for Radiation Protection and Radiation Protection: Many radiation protection devices and accessories are associated with a modern radiology service. Two of these common to all x-ray machines are: -Protective Tube Housing -The Control Panel Many safety features are designed into the modern equipment.
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Deterministic Effects AKA Non-Stochastic: Deterministic Effects - responses increase in severity with increased dose Somatic Effects - happens to exposed individual Threshold - no response below the threshold Like a savings account Example - sunburn --The more you're exposed to the sun, and the higher the 'dose' of sunlight you receive, the more severe the sunburn
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Effects: 1. NONSTOCHASTIC /DETERMINISTIC -threshold dose response relationship, cataracts, sterility -(the more sun the more burn) -Typically large dose/short time -Like a bank account 2. STOCHASTIC: -Random effects non threshold, linear dose response relationship -e.g..: latent cancer, genetic effects -Any amount may cause an effect -The more exposure the more chance of negative effect -Like a light switch
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FACTORS AFFECTING THE BARRIER THICKNESS: 1. Distance from the source : inverse square law applies --Wall and floor mounted tube stands require more shielding on the attaching wall due to protection from tube leakage. 2. Workload: -increase # exams/ week increase in barrier thickness -unit: mA-min../ week -Workload: Busy rooms require more shielding than infrequently used rooms. -Occupancy: The use of the area protected --A closet or storeroom would need less shielding than an office or laboratory occupied 40 hours per week. Use Factor: percent of time in which the beam is aimed at a particular wall. kVp of operation: usually 100 kVp is assumed to be your maximum
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Filtration: All general purpose x-ray units operated at 70 kVp or above required to have -At least 2.5 mm of Al filtration built into the unit. -2.0mm added by manufacturer -0.5mm inherent (Pyrex of tube itself) -Absorbs low energy x-ray Reproducibility: -Output radiation intensity should be consistent from one exposure to another using the same factors. -Checked by making multiple exposures and observing the variation of intensity. -The variation can not exceed 5%. Linearity: -Different combinations of mA and exposure time that equal the same mAs should have same exposure. -When adjacent mA stations are used such as 100 mA or 200 mA and the time is adjusted the intensity should remain the same. --= mAs should give same exposure -When the time is changed, the change should be proportional. --Proportional changes of mAs should give proportional change in exposure and density -The linearity of exposure should be within 10%.
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Four major groups exposed to significant levels of radiation: •Early radiation workers •More than 250,000 survivors of atomic bombs dropped at Hiroshima and Nagasaki. Some survivors had doses approximately 50,000 mrem or more •Individuals who have been involved in radiation accidents (Chernobyl, Three Mile Island, Fukushima) •Patients who have undergone radiation therapy for cancer and other diseases - largest group
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MAXIMUM PERMISSIBLE DOSE - MPD: Maximum radiation dose -would not be expected to produce significant radiation effect (as far as we know) Doses below the MPD should not result in either somatic or genetic response MPDs specified for occupational exposure only Known as dose limiting recommendations Based on a linear, non-threshold dose response relationship - the more radiation, the more chance of ill effect All unnecessary exposure should be avoided
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Man-made sources of radiation: Top Three Sources -Tobacco products (average dose ~1300 mrem/year for smokers) -Medical radiation(total average dose ~ 54 mrem/year) --X rays (total average dose ~ 40mrem/year) ---X rays are similar to gamma rays; however, they originate outside the nucleus. ---A typical radiation dose from a chest X ray is about 10 mrem. -Diagnosis and therapy (total average dose ~14 mrem/year) --In addition to X rays, radioactive materials and radioactive sources are used in medicine for diagnosis and therapy Other sources of man-made sources of radiation exposure: -Building materials (total average dose ~7 mrem/year) -Domestic water supply (total average dose ~5 mrem/year) -Other minor contributors include; --consumer products, industrial sources, and atmospheric testing of nuclear weapons
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More about SECONDARY RADIATION BARRIERS The Control Booth: Lead is rarely required most are adequately protected with 4 thickness of 5/8" sheet rock Control booth is a secondary barrier sheet rock and 1/2" plate glass window often all that is required
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OCCUPANCY FACTOR: Controlled Area: occupied primarily by monitored radiation workers and patients -maximum exposure rate: <100 mR/week Uncontrolled Area: may be occupied by anyone -maximum exposure rate: <10 mR/week
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PARTIAL BODY OCCUPATIONAL EXPOSURE: Lens of the eye: 15 REM/year Skin and any extremity: 50 REM/year -application: fluoro and nuclear medicine -measured by special ring badges or bracelets
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PERSONNEL MONITORING: Records of amount of exposure received Necessary when an individual might receive 10% MPD (radiology personnel only) Film Badges: -Film sandwiched between metal filters in a plastic holder -Density on processed film proportional to exposure received by badge -M = minimum exposure (not recordable) -Must be worn right side up on the collar, outside lead apron (if worn) -Use two if pregnant: collar and waist inside of the lead apron -Never leave in car or near any heat -Wear and replace monthly
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Patient Radiation Exposure Control: 1. Understand and apply the cardinal principles of radiation control: (Based on constant radiation source - i.e. radiation therapy patient rather than diagnostic) this applies to occupational protection Time - the less time, less exposure. Distance - the farther the distance the less exposure. Shielding - the more shielding, the less exposure. 2.Prevent Mistakes and Repeats Do not allow familiarity to result in false security. -Ensure proper patient management and placement -Ensure proper equipment handling and usage -Ensure correct technical factors are set 3.Use Radiation Protective Devices Shields / Filters -Gonadal Protection for all people with childbearing potential when such use will not interfere with the examination. Not since 2019 4."Ten Day Rule" for female patients - changes coming? -Follow the "Ten Day Rule" of selective scheduling for all female patients of child-bearing age (Menarche to Menopause) when obtaining radiographic examinations of the lumbar, pelvis and lower abdomen or spine. --X-raying a pregnant patient should, whenever possible, be avoided, especially during the first trimester. --Schedule between 0-10 days from onset of menstruation -Rules are vague and rely on the facility to set their own procedures 5.Use Beam Restriction / Collimation Always collimate to the smallest field size appropriate for the exam. -Should have ¼" collimation minimally visible around the edges of each film (Most Radiology reference books) -Life University Clinic may request ½" on the edges (- See Clinic intern Radiology handbook) 6.Never hold a patient during an x-ray exam. -Use mechanical restraining devices when possible (as needed). -Otherwise, have oldest relative or friends hold the patient. 7.Always have the person holding the patient wear a protective apron and if possible, protective gloves. 8.Never stand in the primary beam! 9.Always wear protective apparel when not behind a protective barrier. 10.Use radiation monitor devices - more later... -Film Badges and Monthly Service Report --Always wear a radiation monitor and position it outside the protective apron on the collar. --Have "control" monitor in the control room window. --Send badges off for reading and read the returned report
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Personnel Shield: -It must be impossible to make an exposure outside the operator shield or control booth --Must be behind a protective barrier -The exposure button should be attached to the control panel --no long cord -Dead man type switch --requires two fingers to make the exposure.
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Primary radiation: useful beam Primary protective barrier: Wall that the useful beam can be aimed Rarely necessary to use greater than 3 lb/square foot 1/16" lead equivalent concrete, concrete block, brick or dirt may be used instead of lead The walls that are away from the tube direction are secondary barriers. Secondary radiation: 2 types: 1.scatter 2.leakage Secondary radiation barrier: -barriers designed to shield areas from secondary radiation -always less thick than primary barriers -lead rarely required
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Protective Tube Housing: Every x-ray tube must be contained within a protective housing to reduce leakage during operation. The limit or leakage is less than 100 mR/hour at 1m (@3ft).
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Radon Sources of Radiation: •Total average dose ~ 200 mrem/year •Radon: -a contaminant that affects indoor air -from the radioactive decay of uranium -naturally present in the soil. •Radon is a gas -Can travel through the soil and enter through building foundation cracks -greatest concentrations of indoor radon are found in basements. •Radon emits alpha radiation -presents a hazard only when taken into the body (e.g., when inhaled). Radon: •Studies show a clear link between breathing high concentrations of radon and lung cancer •Radon - second most frequent cause of lung cancer after cigarette smoking (about 21,000 deaths per year) •Number one cause of lung cancer among non-smokers • Significant uncertainties exist for the health effects of low-dose exposures. •Radon daughters are solids, stick to surfaces, such as airborne dust particles, can cause lung cancer if inhaled.
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Single Strand DNA Break: •Repairable •Undamaged strand is template •Replicates strand •Cell is repaired OR •A mutation is formed Double Strand DNA Breaks: •Most dangerous of DNA lesions •Diagnostic radiology doesn't cause this •Can be repaired •Cell can die •Cell can mutate
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Source to Image Receptor Distance: A source to image receptor (SID) indicator must be provided. As simple as a ruler or tape measure attached to the collimator Lights attached to the receptor or locks that prohibit exposure unless the SID is correct (not on all machines) SID indicator must be accurate to 2% of the SID.
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Stochastic Effects: Stochastic Effects -increased probability of occurrence with increased dose, -severity is unchanged -Non threshold Somatic or Genetic Effects Example; skin cancer and sunlight. The probability of getting skin cancer increases with increasing exposure to the sun Stochastic Effects are like a light switch; they are either present or not present
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TLD: Thermoluminescent Dosimeter: Absorbs and stores energy in crystal lattice When heated, excited electrons fall back in shell with emission of characteristic visible light Lithium fluoride crystal More sensitive and accurate than film badges Change out every three months
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Terrestrial Sources of Radiation: •Total average dose ~ 28 mrem/year •There are natural sources of radiation in the ground -(i.e., rocks and soil). -Contributors to terrestrial sources are the natural radioactive elements radium, uranium, and thorium. -Many areas have elevated levels of terrestrial radiation due to increased concentrations of uranium or thorium in the soil. Internal Source of Radiation: •Total average dose ~40 mrem/year •Trace amounts from our food and drink •Brazil nuts?
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Two Basic Principles of Radiographic Technology: Radiation Dose (Exposure) - ALARA -As Low As Reasonably Achievable Radiographic Quality - AHARP -As High As Reasonably Possible
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WHOLE BODY NON-OCCUPATIONAL EXPOSURE: 0.1 REM/year used in the design of protective barriers (uncontrolled areas)
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WHOLE BODY OCCUPATIONAL EXPOSURE: 5 REM/year -(5 rem = 5000 mrem) -(average:<100 mRem) Pregnant radiation workers: 0.5 rem/gestation period Never a sufficient reason to terminate employment
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