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  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  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  2.5 kVp  1.5 mm between kVp .5 mm below 50 kVp (mammo)  See question on page 569 (refer to chart 31-3 on page 461)

 Reproducibility  Linearity  Operator shield

MOBILE RADIOGRAPHY  Lead apron assigned to portable  Exposure switch should allow operator to be 2 meter from tube (6+)feet

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

FLUOROSCOPY  Dead man type exposure switch  Bucky opening covered automatically by.25 mm lead  Protective curtain mm Pb equivalent  Timer (audible) when fluoro time has exceeded 5 minutes

FLUOROSCOPY  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

PROTECTIVE BARRIERS

DESIGN CRITERIA  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  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 radiation (scatter, leakage)  Patient is source of scatter  Barrier does not have to be leaded  gypsum board 4 thicknesses of 5/8 th 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  Distance  Occupancy-levels  Control vs uncontrolled  workload  Use factor

USE FACTOR  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  Barriers are designed with 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 1/10 th of the recommended DL

Exposure switch  Mounted of fixed to control panel  No long cords

TLD, OSL