DESIGNING FOR RADIATION PROTECTION - Montgomery College

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26 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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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


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 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)





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
--

.25 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 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 1/10
th

of the recommended DL

Exposure switch


Mounted of fixed to control panel


No long cords



TLD, OSL