Radiation Dose and Protection - Comprehensive 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 can be ionizing or non-ionizing, depending on interaction with matter.

  • Non-ionizing radiation: visible light, heat, radar, microwaves, and radio.

    • It deposits energy in materials and passes through.

  • Ionizing radiation: X-rays and cosmic rays.

    • When ionizing radiation passes through material, it deposits enough energy to break molecular bonds and create charged particles.

    • These 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 \text{mSv} a year from natural radioactive materials and cosmic radiation.

• People living on plateaus in Colorado or New Mexico receive about 1.5 \text{mSv} more per year than those at sea level.

• A coast-to-coast round trip airplane flight results in about 0.03 \text{mSv}.

• The largest background radiation source is radon gas in homes, about 2 \text{mSv} per year (varies widely).

Average Background Radiation

• The average American receives 0.3 \text{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 exist based on elevation.

Man-Made Sources of Radiation

• Receive 0.06 \text{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 \text{rems} from all radiation sources has not been shown to cause humans harm

Sources of Radiation Exposure

• Computed Tomography: 24%

• Nuclear Medicine: 12%

• Occupational: <0.1%

• Interventional Fluoroscopy: 7%

• Conventional Radiography/Fluoroscopy: 5%

• Industrial: <0.1%

• Consumer: 2%

• Terrestrial: 3%

• Internal: 5%

• Medical Background: 37%

• Space: 5%

Average Annual Radiation Dose

• Radon & Thoron: 2.28 \text{mSv}, 228 \text{mrem}

• Computed Tomography: 1.47 \text{mSv}, 147 \text{mrem}

• Nuclear Medicine: 0.77 \text{mSv}, 77 \text{mrem}

• Interventional Fluoroscopy: 0.43 \text{mSv}, 43 \text{mrem}

• Space: 0.33 \text{mSv}, 33 \text{mrem}

• Conventional Radiography/Fluoroscopy: 0.29 \text{mSv}, 29 \text{mrem}

• Internal: 0.21 \text{mSv}, 21 \text{mrem}

• Terrestrial: 0.13 \text{mSv}, 13 \text{mrem}

• Consumer: 0.1 \text{mSv}, 10 \text{mrem}

• Occupational: 0.1 \text{mSv}, 1 \text{mrem}

• Industrial: <0.1 \text{mSv}, <1\text{mrem}

  • Source: National Council on Radiation Protection & Measurements, Report No. 160

Radiation Exposure from Chest X-Ray

• One Chest X-ray = The Radiation Exposure in 10 Days from Natural Surroundings

• One Chest X-Ray = 0.1 \text{mSv} = 10 days background radiation

Average Doses for Common Imaging Procedure

Cigarette Smoking

• Cigarette smoke contains radioactive lead and polonium.

• 1.5 pack/day smoker: the radiation exposure is 1.3 \text{rem/year}.

• Each cigarette = one CXR.

• A non-smoker living with a smoker may receive the equivalent of 12 CXR’s/year from second-hand smoke.

Sources and Doses of Radiation

• Radiation Dose Received from Various Sources of Natural Background Radiation

  • Natural Radiation

    • Cosmic:

      • Quasars, Sun, Supernovas

      • Protons; Electrons Neutrons; Muons

      • Dose Received (mrem/year)

        • 26 (at sea level)

        • 50 (Denver, CO)

    • Terrestrial:

      • Oceans, Lakes, Streams, Rocks, Soil

      • Thorium; Radium; Polonium-210; Lead-210, Potassium-40

      • Dose Received (mrem/year)

        • 16 (Gulf Coast), 30 (Iowa), 63 (Rocky Mtns.)

    • Internal:

      • Food, Milk, Water

      • Potassium-40; Lead-210; Polonium-210

      • Dose Received (mrem/year)

        • 39

    • Atmospheric:

      • Air

      • Primarily Radon

      • Dose Received (mrem/year)

        • 200

• Radiation Dose Received From Other Sources of Radiation

  • Occupational

    • Cigarettes - 1.5 packs/day

      • Lead-210 and Polonium- 210

      • Dose Received

        • 1300 mrem/year

    • Nuclear Medicine Bone Scan

      • Radioactive Technetium

      • Dose Received

        • 430 mrem

    • Living in a Brick House

      • Uranium and Thorium

      • Dose Received

        • 75 mrem/year

    • Watching TV

      • Low Energy X-rays

      • Dose Received

        • 30 mrem/year

    • Routine Chest X-ray

      • X-rays

      • Dose Received

        • 10 mrem/film

    • Cooking/Heating with Natural Gas

      • Radon

      • Dose Received

        • 9 mrem/year

    • Airplane Flight - Cross- Country

      • Cosmic Radiation

      • Dose Received

        • 4 mrem/trip

    • Smoke Detectors

      • Americium-241

      • Dose Received

        • <1 mrem/year

    • Industrial, Medical and Academic

      • \text{0-5000 mrem/year}

      • (Average-500 mrem/year)

    • Nuclear Weapons Fallout

      • Cesium-137; Strontium-90

      • Dose Received

        • <0.3 mrem/year

    • Nuclear Fuel Cycle/Power Plants

      • Nuclear Fuel

      • Dose Received

        • 0.1 mrem/year

Health Effects of Radiation on Living Things

• Three Possible Outcomes

  1. Injured or damaged cells repair themselves, resulting in no net damage.

  2. Cells die, much like millions of cells do every day.

  3. Cells can incorrectly repair themselves, resulting in physical change.

     • Low levels of radiation exposure effects are so small they may not be detected because the body can repair damage caused by radiation.

Traditional Units of Radiation Exposure

• ROENTGEN (R)

  • Measurement of radiation exposure in the air.

  • Measured by the amount of ionization in a given unit of air.

  • (X-ray is neutral in charge).

  • In the SI system, it is measured in coulombs per kilogram (C/kg)

  • Exposure: X-ray tube output, Patient entrance exposure, & scattered radiation

• Dose

  • Amount of energy deposited in material by ionizing radiation.

  • UNITS OF RADIATION DOSE: Gray, RAD, or REM (Ionization within tissue or energy absorbed by tissue)

• RAD (Radiation Absorbed Dose)

  • Primarily used for patient doses

• REM (Roentgen Equivalent in Man)

  • Used for radiation protection.

  • Reporting workers doses with personnel monitors

• In diagnostic radiology, the three units can be considered equal: (1R=1RAD=1 REM) = 0.01 \text{Sieverts} (10 \text{mSieverts})

• 1 \text{Gray(Gy)}= 100 \text{Rads}, and 1 \text{Rad}=10\text{mGy}, 1000\text{mGy}= 1\text{Gy}

Systeme Internationale (SI) Radiation Units

• Exposure Units:

  • Measurement of radiation intensity in the air

  • Measured in Coulombs per kilogram or Gray

• Dose Units:

  • Amount of radiation energy absorbed in tissue (some types of radiation will cause more harm)

  • Measured in Gray

• Equivalent Dose Units

  • Product of absorbed dose and weighting factor = equivalent dose (quantifies the risk for different types of radiation)

  • Measured in Sievert (Sv)

Traditional versus SI

• The SI system has been used since 1958.

• Old units of radiation measurement such as Roentgen, Rad, and Rem, are still in use (similar to the slow conversion to the metric system in the US).

Nuclear Regulatory Commission Dose-Limiting Recommendation

• General Population

  • Annual = 1 \text{mSv} (0.1 \text{rem} or 100 \text{mRem}) for frequent exposure

  • = 5 \text{mSv} (0.5 \text{rem}) or 500 \text{mRem} for infrequent exposure

• Individuals Younger Than 18

  • Should not be employed in situations in which they are occupationally exposed

  • Annual = 1 \text{mSv} (0.1 \text{rem} or 100 \text{mRem})

Technologist Protection (Whole Body Effective Dose)

• Annual = 50 \text{mSv} (5 \text{Rem})

• Because of the small risk of long-term effects of low-level radiation, techs must limit their exposure to the least amount possible, or even less than the allowable 50 \text{mSv} (5 \text{rem}).

• Lifetime Accumulation = 10 \text{mSv} (1 \text{Rem}) x age in years

  • Example: A 50-year-old tech has a max allowable of 500 \text{mSv} (50 \text{Rem})

• Pregnant Technologist (a 2nd monitor should be worn and clearly marked not to mix up the monitors)

  • 0.5 \text{mSv} (0.05 \text{Rem}) during any one month

  • 5 \text{mSv} (0.5 \text{Rem}) for gestation period

Skin Dose vs. Effective Dose

• Different tissues and organs have varying sensitivity to radiation exposure; the radiation risk to different body parts from an x-ray procedure varies.

• During a chest x-ray, only the chest is exposed

• Skin Exposure Dose: 0.05 \text{rem}

• Organs in the chest can be weighted for their biological sensitivity to radiation to come up with a whole-body equivalent dose.

• Whole-body dose: 0.006 \text{rem}

Skin Dose vs. Effective Dose

• Effective Dose (ED)

  • The dose to all organs and their risk of becoming cancerous.

  • In the case of gonads, it's the risk of genetic damage.

  • Used to compare radiation to the whole body from an x-ray procedure with that of natural background radiation.

• Skin Entrance Exposure (SEE)

  • The exposure to the skin where x-ray strikes.

  • The highest numeric value of all the doses, with the least biological effect.

  • As x-ray passes thru the body to the IR, the intensity drops several hundred times.

Personnel Monitoring

• Personnel Monitors

  • Devices worn by personnel who have the potential of receiving more than 10% of the annual occupational effective dose limit (50 \text{mSv}).

  • Must be 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 reading on a timely basis.

Protection

• #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 (Compression bands, sponges, sandbags, tape, pigg-o-stat)

   • Use whenever possible, but as a last resort, use people to restrain.

   • 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 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.

   • The illuminated field will look smaller on patient than actual size

   • Positive beam limitation- built-in and automatically collimates to the 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 effect dose

  • Which set of exposure factors would give the least dose?

    • 1. 500 mA, o.04Sec, 96kVp

    • 2. 500mA, 0.02S, 96kVp

    • 100 mA, 0.1Sec, 110kVp

    • 100mA, 0.01S, 110kVp