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PATIENT and OCCUPATIONAL EXPOSURE and RADIATION PROTECTION

SOURCES OF RULES/GUIDES. NCRP: National Council on Radiation Protection and MeasurementPublishes guidelines and recommendationsOften basis of law from states and other agenciesNRC: Nuclear Regulatory CommissionLaws for users of reactor produced isotopesSets rad protection laws for Nuclear Medi

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PATIENT and OCCUPATIONAL EXPOSURE and RADIATION PROTECTION

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    1. PATIENT and OCCUPATIONAL EXPOSURE and RADIATION PROTECTION

    2. SOURCES OF RULES/GUIDES NCRP: National Council on Radiation Protection and Measurement Publishes guidelines and recommendations Often basis of law from states and other agencies NRC: Nuclear Regulatory Commission Laws for users of reactor produced isotopes Sets rad protection laws for Nuclear Medicine OSHA: Occupational Safety & Health Admin Rules for occupational radiation protection

    3. SOURCES OF RULES (Con’t) FDA: Food and Drug Administration Center for Devices & Radiologic Health (CDRH) Regulates and sets standards for manufacture of electronically produced radiation Regulates users of a mammography ACR: American College of Radiology Publishes standards for practice of radiology Administers accreditation programs for various modalities (Mammo, CT, MRI, etc)

    4. Sources of Radiation in Radiology

    5. LEAKAGE RADIATION Leakage radiation is radiation the passes through the lead shielded protective housing of the x-ray tube when the beam is turned on. By law (FDA), the maximum permissible leakage radiation exposure at 1 meter from a diagnostic x-ray tube is 0.1 R/hour with the tube operating continuously at its maximum kVp and mA.

    6. Occupational Exposure: Scatter

    7. Occupational Exposure Risks Occupational radiation exposure mostly scatter from patient At 1 meter, occupational exposure (if no apron is worn) is 0.1% of that which enters the patient Minimizing patient dose minimizes your dose Occupational Protection: The Cardinal Rules: Time Distance Shielding

    8. Occupational Protection: Time-Distance-Shielding Time: Minimize time spent in exam rooms Should NOT be in exam room during stationary unit radiography

    9. Occupational Protection: Time-Distance-Shielding Distance: Doubling your distance from patient reduces your exposure by 75% (inverse square law) Patient Holding (State law and NCRP guideline) Radiology staff hold only as last resort 1st choice: Family Members 2nd choice: non-occup exposed staff (aide,RN etc)

    10. Occupational Protection: Time-Distance-Shielding Shielding: Properly designed x-ray room shielding (minimal badge readings verify this) Lead garments (aprons, thyroid shields) when not behind protective barrier (portables, fluoro) Other shielding built into equipment also: bucky slot cover (fluoro) Image intensifier housing (fluoro)

    11. Occupational Protection: Time-Distance-Shielding Film Badges: MANDATORY: Facility can be cited and possibly fined if state/OSHA inspectors see staff working without wearing film badges

    12. TIME DISTANCE SHIELDING

    13. Designing for Radiation Protection FACTORS Workload-W: mAs/wk

    14. Designing for Radiation Protection FACTORS Workload: W (mA-min/wk)

    15. Designing for Radiation Protection FACTORS Workload: W (mA-min/wk)

    16. Designing for Radiation Protection FACTORS Workload: W (mA-min/wk)

    17. STEP 3: DISTANCES (D) Distances for inverse square law to calculate primary exposure (if U not 0), scatter and leakage exposure to a point ‘P’ located 1 foot beyond the other side of each barrier. Dscatt: source-skin distance: to calculate patient exposure and thus scatter) Dsec: Distance to ‘P’ from patient: to calculate scatter exposure Dpri, Dleak: Distance to ‘P’ from x-ray tube to calculate primary & leakage exposure

    18. Designing for Radiation Protection FACTORS Workload: W (mA-min/wk)

    19. STEP 4: USE FACTOR (U) The Use Factor (should be Beam Direction Factor) indicates the fraction of time (use) x-rays are directed at a particular barrier Example (chest room): Primary Beam Scatter/Leak Chest stand wall 1 1 Other walls 0 1 Floor 0 1 Ceiling 0 1

    20. Designing for Radiation Protection FACTORS Workload: W (mA-min/wk)

    21. STEP 5: OCCUPANCY (T) Occupancy Factor ‘T’ describes how adjacent areas used: fraction of time given individuals occupy it.

    22. STEP 6: DETERMINE SHIELDING After calculating exposure (R/week) beyond a barrier, required shielding in Half-Value Layers (HVL) or Tenth Value Layers (TVL) is determined. HVL at each kVp: Lead (mm) Concrete (in) 70 kVp 0.15 0.33 100 kVp 0.24 0.60 125 kVp 0.27 0.80 150 kVp 0.29 0.88

    23. EXAMPLE: SHIELDING Non-occupational exposure to office beyond chest room wall (continuous/frequent expos) Limit: 100 mR/year or 2 mR/week 500 R/week at point ‘P’ in office at 125 kVp Must reduce exposure by factor of 250 (from 500 to 2 mR/week): ~ 8 HVLS (1/28 ~ 1/250) 0.27 mm HVLPb x 8 = 2.2 mm Pb ~ 1/12” Pb

    24. NCRP Report 147: (published 2005) Revised guidelines for radiation shielding design. General concepts similar to superceded Report 49 but methods to estimate radiation intensities, use factors, occupancy factors, etc, have been refined and improved. Examples: Assume receptor intercepts/attenuates useful beam Assume negligible leakage for most kVs used More realistic recommendations for use factor

    25. PATIENT EXPOSURE and RADIATION PROTECTION

    26. PATIENT RADIATION EXPOSURE Patient’s risk comes from the primary beam (scatter/leakage negligible in comparison) Risk Indicators: Entrance Skin Exposure Risk Indicators: Organs doses

    27. Patient Entrance Skin Exposure

    28. Patient Entrance Skin Exposure

    29. Where does exposure come from: Population Exposure

    30. PATIENT RADIATION EXPOSURE Patient’s risk comes from the primary beam (scatter/leakage negligible in comparison) Risk Indicators: Entrance Skin Exposure Expressed in Roentgens. Straightforward to calculate Not useful for total risk from multiple exams Risk Indicators: Organs doses Expressed in rads to organ of interest Can directly add doses from multiple exams Common: bone marrow, thyroid, gonadal

    31. Radiology Exposures and Doses

    32. PATIENT RADIATION PROTECTION Adequate Beam Filtration Highest kVp consistent with image quality Fastest film/screens consistent with quality Collimation to area of interest Minimize repeats Minimize fluoroscopy beam-on time Eliminate unnecessary views Proper patient selection

    33. Population Exposure Risk Factors The Issue: If stochastic radiation risks are indeed linear and non-threshold, then “low” doses to a large number of people may result in a significant number of induced radiation effects (eg, cancer) Concern: Medical radiation is increasing, due primarily to increased use of two procedures, each with higher doses than traditional exams: CT and Angiography.

    34. Population Exposure Risk Genetically Significant Dose (GSD): Risk to the population is often expressed as a GSD. GSD is the radiation dose that if received by the entire population, yields the same total effect on the Gene Pool as that of the doses actually received (weighted by age, sex, etc). GSD estimate: 0.2-0.3 mSv/year from medical uses (~1/4 of the gonadal dose from background radiation).

    36. Designing for Radiation Protection Factors: Workload: exams/week, and technique factors (may be given for each kVp range) Exposure corresponding to workload Use Factors: where is x-ray beam aimed ? Distances from radiation source: x-ray tube for primary and leakage, patient: for scatter) Occupancy: how often is area occupied

    37. Designing for Radiation Protection FACTORS Workload: W (mA-min/wk)

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