Transcript Radiation Protection

Radiation Protection
Review of Units of Measurements
Protection for Patient and
Personnel
Review of Radiobiology
Follows the ARRT Content
Specifications
Sources of Radiation
Exposure
Natural or background
- ground, cosmic,
naturally occurring isotopes, etc.
Artificial or man-made -
Medical and
dental largest contributor to population dose
Units of Measurement -
Know traditional and Standard International Units
 Roentgen (R) - traditional unit of exposure in air
- equipment related [x and gamma rays]
Coulomb/Kg or C/Kg
 rad (r) - traditional unit of absorbed dose [all]
•
Gray (Gy)
 rem - traditional unit of dose equivalent [x, beta,
gamma]
– Seivert (Sv)
 Curie
(Ci) -
measure of radioactivity
• Becquerel (Bq) = in Nuc Med
Detection Methods
Personnel

Film Badges - month
Field Instruments

• Cutie Pie,Geiger
Counter
• spills, more industrial
• photographic film

TLD - 3 months
• Sensitive to 5 mrem
• Expensive

Ionization chamber
• pocket dosimeter
• drifts / not accurate
• Larger one for NM or
more industrial
Ionization Counter

Scintillation detector
• more technical use
• used in CT,NM
OSL
 Aluminum Oxide
 Laser beam releases light
 Sensitive to exposures as low as 1 mrem
 3 months at a time
 Can be reanalized
Monitoring Agencies
 NCRP -National Council on Rad Protection
– dose limitations control
 DRH
- Devices for Radiological Health
– radiation control (more equipment related)
 NRC - Nuclear Regulatory Commission
- radiation protection standards
(formerly- Atomic Energy Comm)
 Maryland
State Dept. Health & Hygiene
 EPA - Environmental Protection Agency
– more industrial application related matters
Recommendations for Dose

ALARA - As Low As Reasonably Achievable for patient
and occupational worker

Cumulative Dose Limit for Occupational Worker simply your age x 1 rem
• ie. 47yo male RT, 47 rem

Embyro or fetus -- 50mrem/month or 500 mrem total

Member of public frequently, exposed 100mrem
Interactions with Matter
 Coherent ( Classicial or Thompson)
scattering: < 30kVp
 Photoelectric Effect 30-150 kVp
 Compton’s Scatter: 30-150 kVp
• ie. 70kVp 40% PE and 60% Compton
• vs 100kVp 10% PE and 90 % Compton
 Pair Production and Photodisintegration :
MeV as in Rad Therapy
Estimated Patient Doses
 Skin
- TLD 15, 000mrem and
extremities 30,000 mrem
 Gonad -- genetic responses at 20rads/yr
 Bone Marrow (mean) - rad induced
leukemia 100 rad/yr
 Gonadal
and bone doses are estimates!
Estimated Doses
 Fluoroscopic
are harder to measure
• 2rad/mA/minute
• remember patient becomes the hazard since the
scatter is what gets the radiographer
 Exams
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•
•
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with higher patient doses are:
Fluoro
Angio
Portables
General - around pelvic region, hip femur,
lumbar, coccyx, sacrum
Cardinal Principles
 Time
:  time,  dose OR  time,  dose
 Distance:  distance,  dose
conversely  distance,  dose
OR if you
(don’t forget the inverse
square law or direct square law)
 Shielding: reduces dose as much as 95% in
male patients
Patient Protection

Cardinal Principles
• time, distance, shielding

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Exposure Factors
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kVp, mA, time, distance
directly related
 kVp -  interactions
time -  dose
– fluoro time -keep it short
• mA and  (fast) time

Film Screen Combo
 Beam limitation

Filtration - inherent
• 0.5mm al <50kVp
• 1.5mm al 50-70kVp
PBL - automatic collimation
Cones
Cylinders
aperture diaphragms
•  field, scatter, dose

Avoid Repeats
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techniques charts
good communication
restraining devices
good QA program
Patient Protection continued

Shielding -
not < 0.25mm Pb
• long bones in peds
• all eyes
• gonadal - 5cm primary
–
–
–
–
flat rubber lead strips
shadow shield
shaped or cup
eye shields
• If patient holds
cassette, Pb glove
needs to be 0.5 mm to
protect hand


Air Gap technique
High Dose to
Gonads
•
•
•
•
•
•
•
hip
upper femur
pelvis
lumbar
lumbo-scaral
abdomen
sacrum
coccyx
S-I Joints
BE, IVP, Cysto,
Hystero
Personnel Protection

Cardinal Principles

• Time, Distance,
Shielding

•
•
•
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Protective wear
• Pb aprons 0.5mm =
• Pb gloves 0.25mm =
• thyroid -  dose 10%
& 6mrad per exam
• Pb glasses 0.75mm
–  dose 98%
• Pb sterile gloves
Barriers - 7” high

primary 1/16th inch
secondary 1/32 inch
Pb glass port
mobile in OR
Mobile exposure
cord length - no less 6’
Personnel Protection
Continued

Never hold Patients
- use immobilization

Wear monitoring
devices

apron on tower, bucky slot
cover, fluoro timer
devices

• film badge
• TLD
• Pocket dosimeter
Fluoro equipment -
Clear room when
doing portables or
provide with Pb
apron
 Stand 2 m from
table
Pregnancy

Radiographer
• self disclosure
voluntary
• fetus 50mrem per
month or 500 mrem
or 5mSv over term
• Baby badge at waist
• 0.5mm Pb aprons
are 88% effective >
70 kVp

Patient
• ask about LMP
• ALARA
• double shield or limit
exam views
• 10 day rule for high
dose exams
Rad Protection - Equipment
General Radiographic
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Control panel: light, meters and sound
SID: within  2% variance
PBL: within  2% of SID
Beam alignment
Filtration: 2.5mm Al equivalent total
Reproducibility: output = , not to exceed 5%
Linearity: intensity = across mA stations, not be
exceed 10%
• Personnel shield: short cords so exposures are
made behind 7” barriers
Rad Protection - Equipment
Fluoro and Mobile

Mobile C-Arm:
not < 12” (30cm) source to tabletop
distance

Stationary Fluoro:not < 15” (38cm) source to tabletop
distance

Primary Barrier:

Filtration:

PBL on Fluoro tower:
IA assembly 2mm Pb equivalent when
>125kVp (usually 80-120 kVp fluoro)
2.5mmAl total just in overhead tube; <100mR/Hr
leakage at 1 meter
borders on monitor when IA is
14” from tabletop

Exposure switch:
“Dead man” - intermittent  dose
Rad Protection - Equipment
Fluoro and Mobile

Bucky Slot Cover:
5cm wide at gonadal level and
0.25mm Pb thick

Protective Apron on Tower:
between patient & operator
0.15- 0.25mm Pb
Cumulative Timer for Fluoro: 5 min/audible
 X-Ray Intensity: should not >2.1R/min at tabletop per

mA at 80 kVp
Dose Rate: must not > 10R/min maximum, should not 5
 Front loaded cassette vs back load: front less dose


Spot cassette vs spot film camera -- dose to patient 3x
more for cassette over camera
RADIOBIOLOGY
In addition to the technical side, we
must understand the biological
effects!
Characteristics of Radiation
 Physical
• LET -
efficiency of radiation to produce excitation and
ionization ( energy deposit per unit path length)
• LET of dx is 3 keV/m
• RBE - Relative Biological Effectiveness
Biological Aspects
 Review
the mitosis and meiosis cycles
 The most sensitive time for DNS is G2
and rest of mitotic stages (least during G1


and Synthesis)
Keep in mind that in meiosis, DNS replicates only
once
What about other factor affecting cellular
response?
Laws of Sensitivity
 High
mitotic activity -- more sensitive
 Cell differentiation -- less, more sensitive
 Long dividing future -- more sensitive
• All these Bergonie and Tribondeau



Biological Stress
Pre/post irradiation conditions
Chemicals -- enhancers, protectors
• Ancel and Vitemberger -- more environment related
Effects-- Direct - photon strikes DNA
ladder either rungs or side rails
--breaks in
 Indirect - photon strikes water -- most
abundant so most likely to happen more frequently


Target Theory -- variations, but striking a critical DNA
area where lethality occurs immediately or may take
two hits to achieve death
Cell survival curves - curve representing the dose and
proportion of cells surviving
Mean Survival Curves
 Relationship
between the dose and
number of cells that survive
 Lethal
Dose
• human LD 50/60 -- 350 rad
– previously 50/30 - Chernobyl changed figures
Dose Response Relationships
 Linear,
non-linear
 Threshold
or
non-threshold
 (non-stochastic) (stochastic, random)
 We
practice by Linear, non-threshold
Cellular Responses
 Interphase
death
 Division Delay
 Reproductive failure
Stages of Response
Dose Dependent
 Prodromal
-- NVD
 Latent
 Manifest
• hematologic --dose between 100-1000
– 200-600/200-1000
• GI syndrome - dose between 1000-5000
– 600-1000
• CNS - dose > 5000
 Recovery
or Death
Radiation Reduced Malignancy
 Historical
populations
 Dose related
 Risks associated
 20% population USA will die of Ca
• how do you tell if rad caused?
 Children?
Leukemia is common
In Utero -- Fetal Irradiation
 neonatal
death - 2-3 week of gestation
 malformations
 growth stunting
 congenital defects - functional defects
after week 20
 cancer

induction
Week 4-11 severe abnormalities, especially CNS and
skeletal, while 11- 16 mental retardation &
microcephaly