Designing for Radiation Protection

Design Standards for Radiation Protection – Leakage Radiation

LEAKAGE RADIATION may not EXCEED TUBE HOUSING 100mR / hr or 1 1 meter

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

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

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

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

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

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

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

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

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

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!

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 – 1.5 mm LEAD EQ Pg. 574

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

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 Bucky cover and Curtain: Minimum of 0.25 mm/Pb

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

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

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

Be Safe! Image gently!