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Designing for Radiation Protection

Designing for Radiation Protection. Bushong Ch. 38. Design Standards for Radiation Protection – Leakage Radiation. LEAKAGE RADIATION may not EXCEED. TUBE HOUSING 100mR / hr or 1 mGy/hr @ 1 meter. Control Panel .

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Designing for Radiation Protection

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  1. Designing for Radiation Protection Bushong Ch. 38

  2. Design Standards for Radiation Protection – Leakage Radiation

  3. LEAKAGE RADIATIONmay not EXCEED • TUBE HOUSING100mR / hr or 1 mGy/hr @ 1 meter

  4. Control Panel • Must have an indicator when the x-ray tube is energized. Sometimes it will be a visible light or audible signal or both

  5. SID – Source to Image Distance • Indicator must be accurate to within 2% of the desired SID

  6. Source-to-Skin Distance • SSD is used to describe to distance between the tube and patient during fluoroscopy • SSD must not be less than 38 cm in fluoro rooms and 30 cm for mobile fluoro

  7. Collimation or PBL • Positive-Beam Limitation = PBL • Detects the size of the IR used and automatically collimates to size of the IR at standard SIDs • Used to be required by law between 1974 – 1994 but no longer required. PBL still remains standard in equipment design

  8. Filtration • General-purpose tubes (above 70 kVp) and the fluoroscopic beam must be filtered at least 2.5 mm Al

  9. Reproducibility & Linearity • Reproducibility = consistent exposures • Linearity = any mA station X msec will produce the same mAs

  10. Exposure switch • In diagnostic rooms the switch must be fixed to prevent the ability to make an exposure in the room • Mobile switch must be at least 6 ft long and the dead-man type • Fluoroscopic exposure control should be the dead-man type as well

  11. Radiography Room Design – Factors Affecting Barrier Thickness • Distance – between radiation source and barrier • Occupancy – the use of the area being protected (rarely occupied vs nursing station) • Control area – occupied by radiation workers or patients • Uncontrolled area – occupied by anyone

  12. MONITORING WORK AREAS • CONTROLLED AREA – Used by occupationally exposed personnel (monitored) • 100mrem or 1mSv / WEEK • UNCONTROLLED AREA – PUBLIC • 2 mrem or 0.02 mSv / week*

  13. ROOM SHIELDING • PRIMARY SHIELD = Any wall or portable wall that the primary beam could possibly be directed at • 1/16 Pb or eq. & 7 Feet High • 4 inches of Concrete will do!

  14. ROOM SHIELDING • SECONDARY – NO PRIMARY BEAM • 1/32 LEAD • CONTROL BOOTH – never point the beam at the control panel • BEAM SCATTERS 2X BEFORE HITTING • LEAD WINDOW – 1.5mm LEAD EQ

  15. Bucky Slot Cover & Protective Curtain • What is the minimum Pb eq. ?

  16. Image Intensifier is a primary barrier = 2 mm Pb equivalent CUMLATIVE TIMER FOR FLUORO SIGNALS AFTER 5 MINUTES OF FLUORO TO MAKE SURE THE RADIOLOGIST IS AWARE OF THE BEAM-ON TIME

  17. Exposure Calculations • Exposure = Exposure rate X mAs • Exposure rate varies by kVp selection and distance

  18. Exposure Calculations • At 75 kVp the exposure rate is 2.6 mR/mAs • What is the exposure? • AP Abdomen = 25 mAs • LPO L-spine = 32 mAs • PA Caldwell = 200 mA X 0.10 sec • AP Pelvis = 200 mA X 0.20 sec

  19. Exposure Calculations • 2.6 mR X 25mAs = 65 mR/mAs • LPO L-spine = 32 mAs • PA Caldwell = 200 mA X 0.10 sec • AP Pelvis = 200 mA X 0.20 sec

  20. Be Safe! Image gently!

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