Designing for radiation protection
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DESIGNING FOR RADIATION PROTECTION. TUBE HOUSING. REDUCES LEAKAGE TO LESS THAN 100 mR PER HOUR AT A DISTANCE OF ONE METER FROM HOUSING One meter is 3.3 feet Body parts should not rest on tube housing. Control panel should indicate. Condition of exposure When x-ray tube is being energized

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Tube housing
TUBE HOUSING

  • REDUCES LEAKAGE TO LESS THAN 100 mR PER HOUR AT A DISTANCE OF ONE METER FROM HOUSING

  • One meter is 3.3 feet

  • Body parts should not rest on tube housing


Control panel should indicate
Control panel should indicate

  • Condition of exposure

  • When x-ray tube is being energized

  • kVp, mA or mAs

  • Visible or audible signal of exposure


SID

  • Tape measure or laser lights indicate the distance

  • Must be accurate with 2% of the indicated SID


Collimation pbl beam alignment
COLLIMATIONPBLBEAM ALIGNMENT

  • X-ray beam and light should be within 2% of SID

  • PBL not required anymore

  • Beam should line up with image receptor

  • Proper alignment of beam to film (indicator light)


Filtration
FILTRATION

  • 2.5 mm @70 kVp

  • 1.5 mm between 50-70 kVp

  • .5 mm below 50 kVp (mammo)

  • See question on page 569 (refer to chart 31-3 on page 461)



Mobile radiography
MOBILE RADIOGRAPHY

  • Lead apron assigned to portable

  • Exposure switch should allow operator to be 2 meter from tube (6+)feet


Fluoroscopy
FLUOROSCOPY

  • Source to skin distance – 38 cm

  • Mobile SSD – 30 cm

  • When intensifier is in parked position—no fluoro

  • Intensifier serves as a primary protective barrier and must be 2 mm Pb equivalent.

  • Filtration should be at least 2.5 mm Al equivalent—Tabletop, patient cradle or other material factored in for total filtration

  • Collimation—unexposed border should be visible on TV monitor


Fluoroscopy1
FLUOROSCOPY

  • Dead man type exposure switch

  • Bucky opening covered automatically by .25 mm lead

  • Protective curtain -- .25 mm Pb equivalent

  • Timer (audible) when fluoro time has exceeded 5 minutes


Fluoroscopy2

Intensity (R ) should not exceed 2.1 R per minute for each mA at 80 kVp

DAP

DOSE RESPONSE PRODUCT

DOSE AND VOLUME OF TISSUE IRRADIATED

DAP INCREASES WITH INCREASING FIELD SIZE

FLUOROSCOPY


Protective barriers
PROTECTIVE BARRIERS mA at 80 kVp


Design criteria
DESIGN CRITERIA mA at 80 kVp

  • Location of x-ray table

  • Where is the primary beam directed?

  • Surrounding environment (controlled area vs. uncontrolled area)

  • RF room

  • Dedicated room

  • Use factor

  • # of exams in a room


Primary protective barrier
Primary Protective Barrier mA at 80 kVp

  • Anywhere the primary beam is directed ( dedicated chest rooms)

  • Lead bonded to sheet rock of wood paneling

  • Concrete, concrete block, brick

  • 4 inches of masonry = 1/16 inch of lead

  • Image intensifier considered a primary protective barrier


Secondary barriers
SECONDARY BARRIERS mA at 80 kVp

  • Secondary radiation (scatter, leakage)

  • Patient is source of scatter

  • Barrier does not have to be leaded

  • gypsum board 4 thicknesses of 5/8th inch drywall

  • glass ½ to 1 inch thickness

  • lead acrylic

  • Control booth

  • Lead aprons (5mm of lead attenuates____%_at _____kVp


Factors that affect thickness of barrier
Factors that affect thickness of barrier mA at 80 kVp

  • Distance

  • Occupancy-levels

  • Control vs uncontrolled

  • workload

  • Use factor


Use factor
USE FACTOR mA at 80 kVp

  • Amount of time x-ray beam is directed at wall/floor

  • Wall given a use factor of ¼

  • Floor given a factor of 1

  • Secondary barrier use factor of 1

  • Dedicated chest room-use factor of 1


Finally
FINALLY mA at 80 kVp

  • Barriers are designed with 75-100 kVp usage in mind so most barriers are thicker than needed

  • Exposure to outside of room is calculated to result in a DL of 100mrem per week but do not factor in patient and image receptor interception. DL is actually 1/10th of the recommended DL


Exposure switch
Exposure switch mA at 80 kVp

  • Mounted of fixed to control panel

  • No long cords


Tld osl
TLD, OSL mA at 80 kVp


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