Radiation Safety Issues for Radiologic Technologists Radiation

Radiation Safety Issues for
Radiologic Technologists
Greg Sackett, M.S., CHP
Medical Physicist
Radiation Worker Risks?
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Patient Risks?
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Acute Effects?
Delayed Effects?
Patient Questions?
Radiation Dose Limits
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Dose limits are used to provide a basis for
radiation worker safety
Whole body limits are designed to reduce
stochastic risk (i.e. cancer) to less than 1 in
10,000/yr (10-4 yr-1)
Risk Equivalent to “Safe” Occupations
Additional limits are designed to reduce
deterministic effects (i.e. cataracts)
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NCRP Dose Limits
Category
mrem/yr
Effective dose (whole body)
5000
Lifetime Effective dose
1000 x age
Lens of eye
15,000
Organs, skin, extremities
50,000
Public (frequent exposure)
2% of rad worker (100
mrem)
Public (infrequent exposure)
10% of rad worker (500
mrem)
Embryo/Fetus Total
500
Embryo/Fetus monthly
50
Regulatory Dose Limits
Body Part
Whole Body
NRC/KS Limit
(mrem/yr)
5000
MO Limit
(mrem/yr)
5000
Lens of Eye
15000
5000
Extremities
50000
75000
Pregnant Worker
500
500
Public
100
100
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Typical Occupational Exposures
Category
Uranium miners
Avg. Annual Dose
(mrem)
1200
Nuclear power operations
600
Airline crews
170
Rad and NM Techs
100
Radiologists (NonInterventionalist)
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Scatter - The Source of Operator
Exposure
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Staff do not receive exposure from the
primary x-ray beam
Exposure comes from scattered radiation as
soon as the beam strikes an object (usually
the patient or table)
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Larger patients = more scatter
Higher kVp/mAs = more scatter
Larger field of view = more scatter
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Cardinal Principles of Radiation
Protection*
Time
Distance
Shielding
*External
Exposure Hazards Only
Time
The amount of
exposure an individual
receives is directly
proportional to the
time of exposure.
Therefore, minimize
the amount of time
spent with a radiation
source.
Exposure = Exposure Rate x Time
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Time
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Time of fluoro procedures should be kept to
a minimum
Fluoro should alternate on-off, rather than
constant on
“Pulsed Progressive” fluoro can reduce
patient and caregiver dose by 90% or more
Fluoroscopes have 5 minute reset timers to
remind users of time elapsed
Distance
(Doubling the distance from the source
will decrease the exposure by four)
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Distance
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X-ray, CT, LINAC – staff should be outside
the room (or behind shielding) when machine
is on
Fluoro – remain as far away from patient as
possible when fluoro is on
Just two steps back can greatly reduce
exposure
Immobilization
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If a patient moves
during an exposure, the
image will be blurred
Repeat exam often
necessary, resulting in
increased patient dose
Tech must have patient
cooperation or
immobilize area
Variety of restraining
devices can be used
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Patient Holding
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Mechanical devices should
be used
If mechanical device
impractical, then relative or
friend of patient should hold
Non-radiology workers could
be used as last resort
Protective apparel should
always be worn by holder
In some states, techs holding
patients is illegal or log books
are required
Shielding
Any object between you and a source of
radiation will provide some shielding. In
general, the more dense an object or material,
the better the shield.
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Protective Apparel
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Must be worn during fluoro and
possibly mobile imaging
Lead aprons do not stop 100% of xrays
Recommended to contain at least
0.5mm lead equivalent
CV and Interventionals should use
wrap-around aprons
Aprons must be inspected annually
for leaks and stored appropriately
Correction factors may be applied
for personnel dose calculations
Apron Effectiveness
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Additional Shielding
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Drapes and
equipment aprons
Ceiling mounted face
shields (can reduce
exposure by up to 40
times!)
Mobile shields for
stationary staff like
anesthesia techs
(can virtually
eliminate exposure)
Radiation Safety by Modality
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Fluoroscopy
Interventional
Mammography
CT
Surgery
Mobile
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Fluoroscopy
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Personnel exposure
directly related to
“beam on” time
Tube should be
below patient
Techs should use
ALARA principles to
reduce dose
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Time
Distance
Shielding
Interventional Radiology and
Cardiology
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Exposures higher
due to longer “beam
on” time for
procedures and
cineradiography
Extremity exposures
often significant
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Risk to Patients
Patient Skin Effects
Effect
Fluoro
Cine
Threshold
(rad)
On-time (hr) On-time (hr)
Delay
Transient
Erythema
200
0.7
0.1
Hours
Epilation
300
1.0
0.2
3 weeks
Erythema
600
2.0
0.3
10 days
Moist
Desquamation
1500
5.0
0.8
4 weeks
Dermal
Necrosis
1800
6.0
1.0
> 10 weeks
Secondary
Ulceration
2000
6.7
1.1
> 6 weeks
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Typical Patient Dose
Procedure
Patient Dose
TIPS
217 rad
Nephrostomy
25.8 rad
Neuroembolization—Head
198 rad
Neuroembolization—Spine
374 rad
IVC Filter Placement
19.3 rad
Biliary Drainage
78.1 rad
Hepatic Embolization
196 rad
Percutaneous Coronary
Intervention
200 rad
PTCA & CA
141 rad
Projections
Vertical PA
30° from Vertical
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Projections
Horizontal
Vertical AP
(not recommended)
Proximity of C-Arm to Patient
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Place detector as close
to patient as possible
– Will reduce patient
dose and scatter
Place tube as far from
patient as possible
– Do not remove
spacer cones
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Collimation
• Collimate tightly to
the area of interest.
• Reduces the patient’s
total entrance skin
exposure.
• Improves image
contrast.
• Scatter radiation to
the operator will also
decrease.
Collimation
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Always collimate
as much as
possible
If the video image
is circular you
aren’t collimating
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Mammography
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Low personnel
exposures
Normal walls and
barriers adequate
Dosimetry probably
not required
Mammography Dose
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Primary impact on patient
dose is number of views
(ESE~800 mrem/view)
Therefore, for screening, no
more than 2 views per breast
recommended (4 for
implants)
Tomosynthesis doses are
higher but will likely prevent
additional views
Thyroid shields are not
required
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Computed Tomography
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Personnel exposures
low
Collimated beam
results in low scatter
Personnel can
remain in room if
necessary with lead
aprons
CT Patient Doses
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Only 5% of all exams are CT,
yet CT accounts for ~35% of
patient dose
Approximately 3000 to 5000
mrad for head scan
2000 to 4000 mrad for body
imaging
Highly collimated beam
allows for avoidance of
radiosensitive organs
Patient shielding not usually
necessary
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CT Patient Doses
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Patient doses can be
large (> 6 Gy)
Dependent upon
protocol techniques
(so they should be
reviewed)
Machine reported
CTDI is NOT the
actual patient dose
CT Patient Doses
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CT Dose
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Low noise, high
resolution images result
in high patient dose
Goal is to produce best
possible image with
reasonable dose
Key is proper review of
protocols
Surgery
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Surgery personnel often
concerned about doses
Actual doses are
generally low and staff
are often not provided
dosimetry
Pain Clinic physicians
may be the exception
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Surgery
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Who runs the
equipment?
Portable c-arm
safety techniques
are similar to
interventional rooms
If image quality
acceptable, use low
dose settings
Mobile Radiography
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Usually low personnel
doses
Exposure cord long
enough for tech to be
out of scatter area
Be aware of location of
tube/image receptor
Beware of other
staff/patients/visitors
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Mobile Radiography
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It is often not practical to stand
more than 6 feet away
Techs should wear aprons
Criteria for where to stand:
– Must be able to quickly
access patient
– Must be able to
communicate with patient
– Must be able to
communicate with x-ray
operator
Occupational Radiation Monitoring
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Required if worker expected to
exceed 10% of annual limits
(500 mrem)
Some states require all
machine users to wear
dosimeters
Dosimeters offer no protection,
just record exposure
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Dosimeter Location
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During fluoro
procedures, dosimeter
should be worn on the
collar outside the lead
apron
For non-fluoro users, the
NCRP recommends
wearing the badge at the
waist or chest
Fetal badges should be
worn at the waist, under
a lead apron
Dosimetry Reports
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Dose data must be
maintained
indefinitely
Reports deep dose,
eye dose and
shallow (skin) dose
Maintains current,
quarterly, annual
and lifetime doses
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X-Rays and Pregnancy
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Human body is most
sensitive to radiation
effects before birth
Pregnant Patients?
Effects
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Time Dependent
Dose Dependent
Pregnant Workers
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Radiation workers who become pregnant are
rarely at any significant risk of exposure
Pregnant worker WILL be concerned about
her exposure
Training should be provided to inform her of
potential risks and available options
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Declared Pregnancy
• Pregnant worker may declare
pregnancy to RSO
• Entitles worker to lower dose
limits (500 mrem, 50
mrem/month)
• Additional monitoring
(monthly)
• Possible change of duties
• Cannot be forced to declare
pregnancy
Discussing Risk with Patients
Keys:
l Tell the truth;
l Use positive or neutral terms
and no jargon;
l Use examples to help the
patient understand;
l Don’t speculate, discuss only
the procedure being performed;
l Do not attack the patient’s
beliefs or a source of
misinformation;
l Ask if you are being
understood.
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Discussing Risk with Patients
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Risk of cancer induction
is age dependent
Remember to
emphasize the
BENEFITS of the
procedure
If you can’t answer
question, refer to
Radiologist or RSO
Radiation Safety Officer
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Many institutions
have an RSO
Required by
Radioactive
Materials License
Often a Radiologist
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Radiation Safety Officer Duties
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Ensure workplace safe
for patients and staff
Ensure compliance with
state/federal regulations
Provide safety training
to staff
Counsel patients
Maintain records
Reducing Occupational Exposure
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95% of tech doses come from fluoro and
mobile radiography
Use Time, Distance and Shielding to keep
doses ALARA
Pay attention to fluoro times
Be aware of direction of primary beam
Use provided aprons and shields
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Reducing Unnecessary Patient
Dose
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Unnecessary
examinations
– Radiologist controlled
Repeat Examinations
– Tech controlled
Radiographic Technique
– High kVp/Low mAs
reduces patient dose
– May result in lower
contrast
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QUESTIONS?
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