Designing for Radiation Protection. Design Standards for Radiation Protection – Leakage Radiation.

Designing for Radiation Protection

Design Standards for Radiation Protection – Leakage Radiation

LEAKAGE RADIATIONmay not EXCEED

TUBE HOUSING 100mR / hr or 1 mGy/hr

@ 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 FLUOROSIGNALS AFTER 5 MINUTES OF FLUOROTO MAKE SURE THE RADIOLOGISTIS 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!