Radiation Dose and Protection Notes

Radiation Dose and Protection

Radiation Exists Naturally Everywhere

What is Radiation?

• Radiation is energy given off by matter in the form of rays or high-speed particles.
• Radiation is either ionizing or non-ionizing, depending on its interaction with matter.
  • Non-ionizing radiation: visible light, heat, radar, microwaves, and radio.
    • Deposits energy in materials and passes through.
  • Ionizing radiation: X-rays and cosmic rays.
    • When ionizing radiation passes through material, enough energy is deposited to break molecular bonds and create charged particles.
    • Charged particles can damage plant, animal, and human cells.

Ionizing Radiation from Natural Sources

• The average person in the U.S. receives an effective dose of 3 mSv a year from naturally occurring radioactive materials and cosmic radiation.
• People on the plateaus of Colorado or New Mexico receive about 1.5 mSv more per year than those at sea level.
• A coast-to-coast round trip airplane flight exposes one to about 0.03 mSv.
• The largest background radiation source is radon gas in homes, about 2 mSv per year (varies widely).

Average Background Radiation

• The average American receives 0.3 rems a year of background radiation.
• Terrestrial Radiation:
  • Most exposure comes from radon in the air.
  • Radioactive gas is produced from the breakdown of uranium and radium in soil, rock, and water.
  • All air contains radon.
  • Plants and animals contain radioactive carbon.
  • Water contains small amounts of dissolved uranium and thorium.
  • All people have internal radiation from radioactive carbon and potassium from birth.
• Cosmic Radiation:
  • The sun and stars send a constant stream.
  • Differences in elevation affect exposure levels.

Man-Made Sources of Radiation

• Humans receive about 0.06 rems yearly from man-made sources:
  1. Commercial
  2. Industrial
  3. Medical
• Medical procedures provide the largest amount of human exposure to man-made radiation.
• A yearly dose of 0.36 rems from all radiation sources has not been shown to cause humans harm.

Sources of Radiation Exposure

The data is derived from the National Council on Radiation Protection & Measurements, Report No. 160.

• Radon & Thoron: 2.28 mSv, 228 mrem, 37%
• Computed Tomography: 1.47 mSv, 147 mrem, 24%
• Nuclear Medicine: 0.77 mSv, 77 mrem, 12%
• Interventional Fluoroscopy: 0.43 mSv, 43 mrem, 7%
• Conventional Radiography/Fluoroscopy: 0.33 mSv, 33 mrem, 5%
• Space: 0.29 mSv, 29 mrem, 5%
• Internal: 0.21 mSv, 21 mrem, 5%
• Terrestrial: 0.13 mSv, 13 mrem, 3%
• Consumer: 0.1 mSv, 10 mrem, 2%
• Occupational: 0.01 mSv, 1 mrem, <0.1%
• Industrial: 0.01 mSv, 1 mrem, <0.1%

Radiation Exposure Comparison

• One chest X-ray is equivalent to the radiation exposure in 10 days from natural surroundings.
• One chest X-ray = 0.1 mSv = 10 days of background radiation.

Average Doses for Common Imaging Procedures

Cigarette Smoking

• Cigarette smoke contains radioactive lead and polonium.
• A 1.5 pack/day smoker has a radiation exposure of 1.3 rem/year.
• Each cigarette is equivalent to one chest X-ray.
• A non-smoker living with a smoker may receive the equivalent of 12 chest X-rays/year from secondhand smoke.

Sources and Doses of Radiation

Natural Background Radiation

Other Sources of Radiation

Health Effects of Radiation

• Low levels of radiation exposure effects are often undetectable due to the body's ability to repair damage.
• Possible outcomes:
  1. Injured cells repair themselves, resulting in no net damage.
  2. Cells die.
  3. Cells repair incorrectly, resulting in physical changes.

Traditional Units of Radiation Exposure

• ROENTGEN (R) is a measurement of radiation exposure in the air, measured by the amount of ionization produced in a unit of air.
  • In the SI system, it is measured in coulombs per kilogram (C/kg).
  • Exposure measurement is relevant for X-ray tube output, patient entrance exposure, and scattered radiation.
• Dose is the amount of energy deposited in material by ionizing radiation.
• Units of Radiation Dose: Gray, RAD, or REM, measuring ionization within tissue or energy absorbed by tissue.
• RAD (Radiation Absorbed Dose) is primarily used for patient doses.
• REM (Roentgen Equivalent in Man) is used for radiation protection and reporting worker doses.
• In diagnostic radiology, the units can be considered approximately equal: (1R = 1 RAD = 1 REM) = 0.01 Sieverts (10 mSieverts)
• Conversions:
  • 1 Gray (Gy) = 100 Rads
  • 1 Rad = 10 mGy
  • 1000 mGy = 1 Gy

Systeme Internationale (SI) Radiation Units

• Exposure Units:
  • Measurement of radiation intensity in the air.
  • Measured in coulombs per kilogram (C/kg) or Gray.
• Dose Units:
  • Amount of radiation energy absorbed in tissue.
  • Measured in Gray (Gy).
• Equivalent Dose Units:
  • Product of absorbed dose and weighting factor, quantifying risk for different radiation types.
  • Measured in Sievert (Sv).

Traditional versus SI Units

• The SI system has been used since 1958.
• Old units like Roentgen, Rad, and Rem are still in use.

Nuclear Regulatory Commission Dose Limits

• General Population:
  • Annual: 1 mSv (0.1 rem or 100 mRem) for frequent exposure.
  • 5 mSv (0.5 rem or 500 mRem) for infrequent exposure.
• Individuals Younger Than 18:
  • Should not be employed in situations with occupational exposure.
  • Annual: 1 mSv (0.1 rem or 100 mRem)

Technologist Protection Dose Limits

• Annual (whole body effective dose): 50 mSv (5 Rem)
• Limit exposure to the least amount possible, even less than 50 mSv (5 rem).
• Lifetime Accumulation: 10 mSv (1 Rem) * age in years
  • Example: A 50-year-old tech has a maximum allowable accumulation of 500 mSv (50 Rem).
• Pregnant Technologist:
  • A second monitor should be worn and clearly marked.
  • 0.5 mSv (0.05 Rem) during any one month.
  • 5 mSv (0.5 Rem) for the gestation period.

Skin Dose vs. Effective Dose

• Different tissues and organs have varying sensitivity to radiation exposure, causing radiation risk to vary.
• During a chest x-ray, only the chest is exposed.
• Skin Exposure Dose: 0.05 rem
• Whole Body Dose: 0.006 rem

Skin Dose vs. Effective Dose

• Effective Dose (ED):
  • The dose to all organs and their risk of becoming cancerous, or in the case of gonads, the risk of genetic damage.
  • Used to compare radiation to the whole body from an x-ray procedure with the dose received from natural background radiation.
• Skin Entrance Exposure (SEE):
  • The exposure to the skin where x-ray strikes.
  • The highest numeric value of all doses.
  • Least biological effect.
  • As x-ray passes through the body to the IR, the intensity drops several hundred times.

Personnel Monitoring

• Personnel Monitors are devices worn by personnel who have the potential of receiving more than 10% of the annual occupational effective dose limit (50 mSv).
• Worn at waist or chest level, except in fluoroscopy where it should be worn at the collar, outside the lead apron.
• Pregnant women wear a second one at waist level under the lead apron.
• Monitors should be turned in for readings on a timely basis.

PROTECTION

• The #1 responsibility of a technologist is to protect themselves, co-workers, and patients from excessive radiation……
• ALARA

ALARA: For Occupational Exposure

1. Always Wear a Personnel Monitor Device
   • Accurate records are important to protection practices.
2. Mechanical Holding Devices
   • Use compression bands, sponges, sandbags, tape, pigg-o-stat whenever possible.
   • Use people to restrain as a last resort.
   • This should be done by a person other than radiology personnel.
3. Collimation, Filtration, kVp, Minimum Repeats
   • Tech exposure is primarily scatter from the patient.
   • Reduce patient exposure = reduced tech exposure.
4. Three Cardinal Principles: Time, Distance, Shielding
   • Important in portables, fluoroscopy, and C-Arm especially.

Tech Protection During Fluoroscopy

• Patients give off scatter radiation.
• Exposure levels drop with distance.
• The intensifier tower, lead drapes, bucky slot cover all shield some of the exposure.

Shielding

• Everyone involved with a fluoroscopic procedure or a portable C-arm MUST wear a lead apron.
• Cut-outs for arms and neckline should not be large.
• To protect lungs and breasts
• Thyroid shields must be worn also.

Patient Protection

1. Minimum Repeats
   • Poor communication
   • Fully explain breathing instructions
   • Bad positioning
   • Incorrect exposure factors
2. Highest acceptable kVp
3. Correct Filtration
   • Reduces exposure to the patient by reducing lower-energy (unusable) x-rays.
   • Inherent (built-in) Filtration
   • Added Filtration: between the x-ray tube and collimator, and within the collimator.
4. Use at least 40 inch SID
   • Tube housing leakage

Patient Protection Continued

5. Accurate Collimation
   • Essential to reduce patient exposure.
   • Limit size and shape of x-ray beam to only the area of interest.
   • Reduces the volume of tissue radiated.
   • Reduces amount of scatter.
   • Illuminated field will look smaller on the patient than the actual size.
   • Positive beam limitation: built-in and automatically collimates to size of cassette.
   • If possible, reduce collimation field even more.

Patient Protection Continued

6. Specific Area Shielding
   • Used when radiosensitive tissues or organs are in or near the useful beam (thyroid gland, breasts, and gonads).
   • Shadow shields and Contact shields.
   • Gonadal Shielding is the most common area done.
   • Gonadal shielding reduces dose 50%-90% if gonads are in the primary beam.

Rules for Shielding

1. It should be used on all potentially reproductive-age patients.
   • Good Practice: shield ALL gonads for all patients when possible in reproductive years.
   • Consist of at least 0.5mm lead.
2. It should be used when radiation-sensitive areas lie within or near (2 inches or 5 cm) the primary beam unless it covers diagnostic information.
3. Accurate beam collimation and careful positioning
   • Never a substitute for accurate beam collimation.

Patient Protection Continued

• Protection for Pregnancies
  • Pregnancies and potential pregnancies require special consideration for women.
  • Most critical in the first 2 months of pregnancy
  • Fetus most sensitive
  • In the past, the 10-day rule was used
  • All radiologic exams involving the lower abdomen/pelvis should be scheduled during the 1st 10 days
  • Considered obsolete

Patient Protection Continued

• Exposure Factors with the Least Patient Dose
• Technologists should understand the various combinations and how they affect dose
• Which set of exposure factors would give the least dose?
  • 1. 500 mA, 0.04 Sec, 96kVp
  • 2. 500mA, 0.02S, 96kVp
  • 100 mA, 0.1 Sec, 110kVp
  • 100mA, 0.01S, 110kVp