Designing for Radiation Protection

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Designing for Radiation Protection
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Design Standards for Radiation Protection
Leakage Radiation
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LEAKAGE RADIATIONmay not EXCEED

• TUBE HOUSING 100mR / hr or 1 mGy/hr
• _at_ 1 meter

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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

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SID Source to Image Distance

• Indicator must be accurate to within 2 of the
  desired SID

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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

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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

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Filtration

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

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Reproducibility Linearity

• Reproducibility consistent exposures
• Linearity any mA station X msec will produce
  the same mAs

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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

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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

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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

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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!

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ROOM SHIELDING
Pg. 574

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

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Bucky Slot Cover Protective Curtain

• What is the
• minimum
• Pb eq. required ?

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Image Intensifier is a primary barrier 2 mm Pb
equivalent
Bucky cover and Curtain Minimum of 0.25 mm/Pb
CUMLATIVE TIMER FOR FLUORO SIGNALS AFTER 5
MINUTES OF FLUORO TO MAKE SURE THE RADIOLOGIST IS
AWARE OF THE BEAM-ON TIME
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Exposure Calculations

• Exposure Exposure rate X mAs
• Exposure rate varies by kVp selection and distance

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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

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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

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Be Safe! Image gently!