radiation and protection

RADIATION SAFETY AND PROTECTION (Dr. Virginia Theresa Facto-Tampus Roentgenology)

Sources of Radiation

  • Total Average Annual U.S. Radiation Dose: 6.2 mSv

    • Approximately 50% from natural sources and 50% from synthetic sources.

    • Natural sources contribute an average of approximately 310 millirem (0.31 rem) per year.

    • Synthetic sources contribute the same average of approximately 310 millirem (0.31 rem) per year.

Breakdown of Radiation Sources

  • Cosmic (Space): 5%

  • Terrestrial (Soil): 3%

  • Radon and Thoron: 37%

  • Internal Sources: 5%

  • Medical Procedures: 36%

  • Industrial and Occupational: 0.1%

  • Nuclear Medicine: 12%

  • Consumer Products: 2%

Radiation Exposure Summary

  • Natural/Background Radiation:

    • Radon: 200 mrem/year (2.00 mSv/year)

    • Cosmic: 27 mrem/year (0.27 mSv/year)

    • Terrestrial: 28 mrem/year (0.28 mSv/year)

    • Internal: 39 mrem/year (0.39 mSv/year)

  • Artificial/Human-Made Radiation:

    • Medical or Dental: 53 mrem/year (0.53 mSv/year)

    • Consumer Products: 9 mrem/year (0.09 mSv/year)

    • Occupational: <1.00 mrem/year (<0.001 mSv/year)

    • Nuclear Fuel Cycle: <1.00 mrem/year (<0.001 mSv/year)

    • Fallout: <1.00 mrem/year (<0.001 mSv/year)

Risk and Risk Elements

  • Definition of Risk: Likelihood of adverse effects or death resulting from exposure to a hazard.

    • Ionizing Radiation Risk: Likelihood of an adverse effect, specifically cancer induction, occurring from exposure to ionizing radiation.

    • Estimated Risk for Dental Imaging Inducing Fatal Cancer: Approximately 3 in 1 million.

    • Spontaneous Cancer Rate: Approximately 3300 in 1 million.

Specific Dose Risks

  • Bone Marrow (Leukemia Induction): Induced at doses of approximately 5000 mrad (0.05 Gy).

  • Eyes (Cataract Formation): Requires doses greater than 200,000 mrad (2 Gy).

  • Skin (Erythema): Occurs with a total dose of 250 rad (2.5 Gy) in a 14-day period.

  • Thyroid Gland Cancer Induction: Estimated dose required is 6000 mrad (0.06 Gy).

Patient Exposure and Dose Management

Techniques to Reduce Exposure:

  • Technique: Use of the paralleling technique and increased target-receptor distance.

  • Collimation: Use of rectangular collimation minimizes exposure (60%-70% efficiency).

  • Receptor Choice: Incorporating sensors reduces patient exposure (50%-90% efficiency).

Effective Doses Associated with Common Radiographic Examinations

  • Effective Dose Range in Microsieverts (µSv):

    • 1 BW/rectangular collimation: 1.5

    • 4 BW/rectangular collimation: 3

    • 1 BW/round collimation: 4

    • Panoramic: 16

    • Complete series/rectangular collimation: 35

    • CBCT/large field of view: 68

    • Complete series/round collimation: 89

International Radiation Protection Recommendations

Recommended Dose Limits for Human Exposure to Ionizing Radiation

  • Occupational Exposure Limits:

    • Effective dose: 20 mSv per year (averaged over a defined period of 5 years).

  • Public Exposure Limits:

    • 1 mSv per year.

    • Annual equivalent dose to lens of eye: 15 mSv with a maximum of 50 mSv in any one year.

  • Skin Dose Limit: 500 mSv per year for occupational exposure, 50 mSv for public exposure.

  • Hands and Feet: 500 mSv for occupational exposure.

ALARA Principle

  • ALARA: As Low As Reasonably Achievable, ensuring that exposures to ionizing radiation are minimized with economic and social factors considered.

Optimizing Dental Radiographs

  1. Justification: Determine whether diagnostic exposure benefits outweigh risks.

  2. Optimization: Employ all reasonable means to reduce unnecessary exposure to patients and staff.

  3. Dose Limitation: Expose individuals to doses not exceeding recommended limits to prevent unacceptably high doses.

Equipment and Safety Protocols

Filtration Types

  • Inherent Filtration: Occurs when the primary x-ray beam passes through the x-ray tube’s glass window and other materials.

  • Added Filtration: Incorporates aluminum disks in the x-ray beam path to reduce patient exposure, with a required minimum of:

    • 1.5 mm total filtration for machines at or below 70 kV, and 2.5 mm for machines above 70 kV.

Collimation

  • Collimator Types:

    • Circular collimator produces a 2.75-inch diameter beam, larger than the intraoral receptor size.

    • Rectangular collimator restricts beam size to just larger than the receptor, thereby minimizing exposure.

Position-Indicating Device (PID)

  • Long (16-inch) PID: Preferred due to less beam divergence compared to a shorter (8-inch) PID.

Patient Protection During Dental Radiographs

  • Thyroid Collar: Flexible lead shield for protecting thyroid.

  • Lead Apron: Shielding for reproductive and blood-forming tissues.

  • Digital Image Receptors: Require less radiation than traditional methods.

  • Fast Film (F-Speed): Provides 20% reduction in exposure vs. E-speed films, and 60% reduction compared to D-speed films.

Operator Protection Guidelines

  • Operator Positioning: Stand at least 6 feet away from the x-ray tubehead during exposure.

    • Use leaded glass barriers for additional safety.

    • Avoid direct exposure to primary beam: stand at 90°-135° angle to minimize dose from scattered radiation.

Radiation Monitoring

  • Monitoring Equipment: Staff should use radiation monitoring badges to track exposure levels.

  • Maximum Permissible Dose: Defined as 50 mSv/year for occupationally exposed persons.

    • Protective measures for pregnant dental workers (0.5 mSv/month during pregnancy).

ALARA Approach

  • Ensuring Safety: Continuous efforts to minimize radiation exposure to both patients and operators, employing necessary protection and procedural adherence.