chapter 13 EXAM 6 FINAL Flashcards
for monitored xray personnel the risk may be compared with the occupational risk for persons employed in other industries considered reasonably safe. These jobs have a risk of fatal accidents generally estimated to be about
1x10^-4 per year
1 in 10,000 a year
at a 90 degree angle to the primary xray beam at a distance of 1m the scattered xray intensity is generally about how much of the primary xray beam
about 1/1000 of the intensity of the primary xray beam
what poses the greates occupational hazard in diagnostic radiology
scattered radiation
what reduces the number of scattered radiation produced in a pt. and therefore reduces the radiographers dose
beam limitation devices
for regular diagnostic xrays, your protective lead apron should be how much lead
0,25
for fluoro your protective lead apron should be how much lead
0.5
all aprons should be inspected for cracks or other defects every
year
as the average energy of the beam increases, the percentage of radiation that is forward scattered does what and therefore…
increases
and therefore less side scattered radiation is available to strike imaging personnel
use of high speed image receptors does what to the personnel exposure
decreases personnel exposure
after the voluntary declaration of pregnancy, the RSO must
provide essential counseling
furnish an appropriate additional dosimeter
in pregnant personnel, the monthly EqD to the embryo fetus must not exceed
0.5mSv
in pregnant personnel, the EqD for the entier pregnancy must not exceed
5 mSv (0.5rem)
attenuation by the maternal tissues ovelying the fetus reduces the dose to the fetus to aprox.
30 % of the abdominal dose
t or f
when normal protective measures are taken it is nearly impossible for a radiographer to approach the fetal dose limit of 5mSv
true
specially designed maternity protective aprons consist of what lead equivalent over the entire length and width
0.5 mm lead equivalent
specially designed maternity protective aprons also have an extra what equivalent of lead protective panel that runs transversely across the width of the apron
1mm lead equivalent
3 basic principles of radiation protection
time
distance
shielding
the amt of radiation a worker receives is directly or indirectly proportional to the length of time the individual is in the path of ionizing radiation
directly proportional
exposure =
exposure rate * expsoure time
what is the most effective means of protection
distance
inverse square law
expresses the relationship between distance and intensity
I1/I2=D2^2/D1^2
the intensity of radiation is inversely or directly proportional to the square of the distance from the source
inversely
if you double the distance, the dose reduces by
4
if you triple the distance the dose reduces by
9
2 types of protective shielding
- structural protective barriers
2. accessory protective devices
structural protective barriers include
lead
concrete
accessory protective devices include
aprons
gloves
thyroid shields
protective glasses
protective structural shielding includes
walls and doors in xray room to shield form personnel and general public
whose responsibility is it for determining the exact protection requirements for a particular imaging facility
the medical physicist
primary protective barrier
barrier designed to shield an area from primary radiation
what is the purpose of a primary protective barrier
to prevent direct or unscattered radiation form reaching personnel or general public located on the other side of the barrier
if the peak energy is 130 kVp the primary protective barrier in a typical installation consists of
1.6 mm lead
when the xray tube is 1.5-2.1m from the wall in question, the primary protective barrier must extend upward
2.1m
secondary protective barrier
barrier designed to shield an area from secondary radiation
what is the purpose of a secondary protective barrier
to protect against leakage and scatter radiation
a secondary barrier should overlap the primary protective barrier by aprox
1.27cm
in a typical installation the secondary barrier consists of how much lead
0.8mm lead
control booth barrier must extend how high upward and be permanently secured to the floor
extend 2.1m up from the floor
the lead glass window consist of how much lead
1.5mm lead equivalent
appropriate lead equivalent in the control booth ensures the radiographer will not exceed a max allowance of what per week
1mSv per week
in a well designed facility exposure to personnel should not exceed what per week
0.02mSv per week
modular xray barriers are available in what lead equivalent
0.3-2mm
clear lead acrylic overhead protective barrier
used as overhead xray barriers to provide open view during special procedures and heart catheterizations
when lead equivalent thickness increases…
attenuation increases when kVp stays the same
a what mm lead apron would be appropriate for mamo
a 0.25mm lead apron
the neck and thyroid shield should be a minimum of what lead equivalent
0.5mm lead
in protective eyewear, the lenses contain a minimal lead equivalent of
0.35mm lead
the methods and devices that reduce exposure to personnel during fluro are
adequate beam collimation adequate filtration gonadal shielding control of exposure factors use of high speed image receptors appropriate Source to skin distance
the bucky slot shielding device must be at least what lead equivalent
0.25 lead eq
without the bucky slot cover and the protective curtain in place the exposure rate for fluoroscopists would exceed what at a distance of what
1mGya/hr at a distance of 0.6m (2ft)
where should the radiographer stand during mobile radiographic procedures
at a right angle to the xray beam
in routine fluoro the max allowed entrance exposure rate dose to a pt. is
10 cGy/minute
in HLC fluoro the max allowed entrance dexposure rate dose to a pt. can range upward to
20-40 cGy/minute
NCRP currently recommends an annual EqD limit to the localized area of the skin and hands of
500 mSv
most facilities room doors have attenuation for diagnostic energy xrays equivalent to that provided by
0.8mm of lead
what are the 3 categories of radiation that can be generated in an xray room
primary radiation
scatter radiation
leakage radiation
what part of the xray room requires the most protective shielding for safety purposes
the wall in the path of the direct radiation
in a typical xray room the most important primary barrier is
behind the wall bucky unit
if the xray tube housing is designed properly the leakage radiation will never exceed the regulatory limit of
1mGya/hr
a busy general purposed xray room may have a workload of
500mA-min/week
rooms in private offices may have workloads of less than
100mA-,in/week
workload definition
product of the max mAs and the number of xray examinations performed each week
use factor (U)
the percentage of time during which the xray beam is on and directed toward a primary protective barrier
the use factor is also called
the beam factor
occupancy factor (T)
a factor used to modify the shielding requirements for a particular barrier by taking into account the fraction of the work week during which the space beyond the barrier is occupied
controlled area
a region adjacent to a wall of an xray room that is occupied by only occupationally exposed workers
uncontrolled area
a region adjacent to a wall of an xray room such as a corridor or hall that is frequented by the general public
for uncontrolled areas the weekly max permitted equivalent dose is equal to
20 microsieverts which is .02 mSv
for controlled areas the weekly max permitted equivalent dose is equal to
1000 microsievert or 1 mSv
