Nuclear Medicine Physics
Radiation Protection
in Nuclear Medicine
Jerry Allison, Ph.D.
Department of Radiology
Medical College of Georgia
A note of thanks to
Z. J. Cao, Ph.D.
Medical College of Georgia
And
Sameer Tipnis, Ph.D.
G. Donald Frey, Ph.D.
Medical University of South Carolina
for
Sharing nuclear medicine presentation content
Federal Register/Vol. 80, No. 220/ November 16, 2015/Notices
NUCLEAR REGULATORY COMMISSION
[NRC–2015–0020]
Sodium Iodide–131 Patient Release Information Collection
AGENCY: Nuclear Regulatory Commission.
ACTION: Request for information.
SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is requesting
information from the general public on a number of issues associated
with medical treatment of patients with sodium iodide I–131 (hereafter
referred to as I–131). Specifically, the NRC would like input on patient
concerns about medical treatment involving the use of I–131, information
that physicians use to make decisions on when it is safe to release I–131
patients based on radiation exposure concerns, radiation safety
information used by I– 131 patients after their release, and the availability
of a radiation safety informational guidance brochure for I– 131 patients
that can be distributed nationwide. The information collected will be used
to develop a Web site to provide patients with clear and consistent
information about radioactive iodine treatments and to revise NRC patient
release guidance.
UCSD Imaging Research
4
UCSD Imaging Rersearch
5
Radiation exposure of the public
6
Sources of low-dose radiation
1982 data of NCRP: 4.6 mSv/person/yr
• Natural background: 4 mSv/person/yr (88%)
 Radon at home: 2.57 mSv/person/yr (56%)
 Other sources: 1 mSv/person/yr (22%)
e.g. U-238 and Th-232 in soil, cosmic rays
from the sky, and internal radiation from 40K,
14C and 3H
 Fallout from nuclear power stations and
consumer products: 0.46 mSv/person/yr
(10%)
7
• Medical: 0.54 mSv/person/yr (12%)
Sources of low-dose radiation
2006 data of NCRP: 6.7 mSv/person/yr
• Natural background: 3.5 mSv/person/yr (52%)
• Dramatic increase of medical dose from
0.54 to 3.2 mSv/person/yr (12%  48%)
 CT dose: ~ 1.6 mSv/person/yr (50% of
medical)
 NM dose: ~ 0.8 mSv/person/yr (25% of
medical)
• Dramatic increase of NM and CT studies:
1984
2006
NM
6M
18 M (3% of all)
CT
3M
67 M (12% of all)
8
Radiation dose effects
9
Stochastic and non-stochastic
effects
• Stochastic: The frequency of effects in a
population depends on dose without
threshold (e.g. cancer).
• Non-stochastic: The severity of effects varies
with dose above threshold (e.g. cataracts).
• Aim of radiation protection: to prevent nonstochastic effects by limiting the radiation dose
received as well as to reduce the probability of
stochastic effects through ALARA practice.
10
Models of low-dose response
• Lack of certainty for low dose effects
(< 1 Sv/yr)
• Linear no threshold (LNT) model: a line
connecting the bottom end of high-dose
response curve to the zero dose
• Linear-quadric model: linear for the lowest dose
and quadric for the remainder
• Hormesis model: ‘J’ shape  dangerous at high
dose but beneficial at low dose, low dose
sterilizing cancer cells and stimulating cell
activities
11
Models of low-dose response
damage
linear+quadric
1 Sv/yr
hormesis
dose
benefit
12
Internal dosimetry
• Factors determining internal dose
• Medical internal radiation
dosimetry (MIRD) calculation
schema
13
Factors determining
internal dose
• Administered activity
• Initial activity in the source organ and the length
of stay in the organ, depending on
biodistribution and physical decay
• Energy emitted per decay
• Absorbed fraction by the target organ,
depending on distance, attenuation, and target
organ volume and composition
14
Factors determining internal
dose
• Source and target organs
15
MIRD calculation schema

Mean absorbed dose
D = ÃS orD/A0 = tS
Where t = Ã /A0
• A0: administered activity. It is known.
• Ã is activity accumulated in the source organ
and t is the residence time. Ã or t depends on
initial biodistribution, physical decay (lp), and
biologic behavior (lb). It can be estimated by
imaging at multiple times.
16
MIRD calculation schema
• S: dose to the target organ from unit cumulated
activity in the source organ
• S has been tabulated for many organs and also for
many radiopharmaceuticals.
• S depends on radiation energy per decay and
absorbed fraction by the target organ f.
• 0 < f < 1, determined by photon energy and
distance, attenuation, volume and composition of the
target organ
17
Absorbed dose to individual
organs
F18FDG(10 mCi)
Tc99mECD(30 mCi)
Tl (3 mCi)
brain
17 mSv
0.4
6.6
kidneys
7.8
5.8
51
heart
25
1.3
3
ovaries
4.1
5.8
11
testes
4.1
2.6
22
Spleen
5.6
1.5
2
bladder
27
54
5.7
______________________________________________
EDE
8.6 mSv
8.4 mSv
18 mSv
18
Effective dose of NM procedures
19
ACOB/GYN’s statement
and regulations
• “Women should be counseled that x-ray
exposure from a single diagnostic procedure
does not result in harmful fetal effects.
Specifically, exposure to less than 50 mGy
has not been associated with an increase in
fetal anomalies or pregnancy loss.”
• Regulatory dose limit for the fetus of a
declared pregnant worker is 5 mSv during
the pregnancy.
20
Absorbed dose to fetus
early 1st
end of 1st
trimester
trimester
_______________________________________
bone scan
(20 mCi 99mTc-MDP)
5 mSv
4 mSv
WB PET scan
(15 mCi 18F-FDG)
15 mSv
10 mSv
thyroid scan
(0.2 mCi 123I)
0.2 mSv
0.1 mSv
all dose << 50 mSv
21
Absorbed dose to fetus
• Iodine can cross the placenta but fetal thyroid
does not cumulate iodine before 12 wk of
gestation.
• Mental retardation from radiation occurs
primarily at 8 to 15 weeks of gestational
period.
• A large portion of radiation comes from
mother’s bladder so hydration and frequent
voiding may reduce the radiation.
22
Radiation protection
• U.S. Federal regulations (10CFR 19, 20,
and 35)
• ALARA: philosophy of radiation use
whereby radiation dose is “as low as
reasonably achievable”
23
Regulatory agencies
• Nuclear Regulatory Commission (NRC)
To regulate the nation's civilian use of byproduct, source,
and special nuclear materials to ensure adequate
protection of public health and safety, to promote the
common defense and security, and to protect the
environment. The NRC's regulatory mission covers three
main areas: reactor safety, radioactive materials used in
medicine, industry and research, and nuclear waste
management
• FDA
To regulate radio-pharmaceuticals and NM devices
24
Regulatory agencies
• EPA
To regulate the radiation released to environment
• DOT
To regulate the transportation of radioactive
material
• Agreement States
To enter an effective regulatory discontinuance
agreement with the NRC to regulate most types of
radioactive material in accordance with the compatibility
requirements of the NRC
25
Agreement States
37 states have signed an agreement with the
Nuclear Regulatory Commission stipulating
that they will be the sole regulators, but will
follow Federal guidelines. They may be more
restrictive than these guidelines, but not less
restrictive.
In August, 2013, the NRC put the state of Georgia on
probation due to multiple failures. The next review was set to
be in January, 2014. The State passed the review.
26
Agreement States (2015)
https://scp.nrc.gov/rulemaking.html
27
Advisory bodies
• International Commission on Radiological
Protection (ICRP)
• U.S. National Council on Radiation
Protection and Measurements (NCRP)
• International Atomic Energy Agency
(IAEA)
• Conference of Radiation Control Program
Directors (CRCPD)
28
“Radiation badges”
• Anybody that may receive 1/10 of the annual
occupational dose limit of 50 mSv needs to
wear a radiation badge.
• Minor likely to receive:
 Annual external dose (DDE) > 1 mSv
 LDE for eyes > 1.5 mSv
 SDE for skin > 5 mSv
• If the waiting area for injected patients is close
to the secretary, she/he should wear a radiation
badge.
How to wear a radiation
badge?
• For uniform radiation exposure, wear the
badge on front of upper torso.
• If particular body part is more exposed,
wear the badge as close to this part as
possible.
• Wear the badge behind a lead apron (or at
the collar outside the apron, GRU policy)
• A person handling radionuclides must wear
30
both whole body and ring badges.
How often are badges exchanged?
• Every month @ GRU
 OSL = Optically Stimulated luminescent
Dosimeter
• Monitoring is only required for external
exposure. There is NO requirement to
monitor the internal exposure.
Posting of badge reports
Film badge readings are routinely posted
on bulletin board on a monthly basis.
Employer is responsible for informing
each employee on an annual basis of
his cumulative radiation dose.
Occupational dose limits
• Occupational dose limits:
For an adult worker < 50 mSv/yr
For an individual organ < 500 mSv/yr
For the eye lens < 150 mSv/yr
For fetus of a pregnant worker < 5 mSv/pregnancy
General public limits:
Dose < 1 mSv/yr
Exposure rate < 2 mR in any given hour
33
Declared pregnant radiation workers
• A declared pregnancy is when an employee
voluntarily informs the radiation safety office in
writing of her pregnancy and estimated date of
conception.
• It is entirely the choice of the worker.
• NRC dose limit is 5 mSv (10% of the annual
occupational dose limit) to the fetus for the entire
pregnancy.
• An additional dosimeter badge should be worn at
the level of the fetus.
• If a worker chooses not to declare her
pregnancy, the pregnancy dose limit does not
apply.
Radiation dose to the hands
• Typical dose received by hands without
syringe shields is 5 to 10 mSv/hr/mCi
when handling radionuclides.
• For a radiation worker to reach the 500
mSv per year limit, she/he could spend
5-10 hours handling a 10 mCi
syringe per year.
• Syringe shields reduce the
dose by a factor of 3.
Radiation exposure rate
around patient
Typical exposure rate at 1 m from the
patient soon after injection:
• Most radiopharmaceuticals:
1 mR/hr (maximum dose to public 1
mSv/yr)
•
18F-FDG:
•
131I:
5 - 30 mR/hr
5 or 30 mR/hr for Graves or
cancer dose respectively
Surveys for contamination
• Survey with a GM meter must be performed at the end
of each day in all areas where radioactive materials
are prepared or administered.
• The GM meter must be able to detect an exposure
rate as low as 0.1 mR/h.
• Wipe tests must be performed once a week where
radioactive materials are prepared, administered or
stored.
• A record of the results should be kept.
Area surveys – daily
• Using a GM meter, survey each room in
which radioisotopes are used.
• Record Model # & Serial # of the GM
meter
• Record actual reading; specify units (cpm
or mR/hr)
• Record background reading
• Specify "action level" (criterion for
immediate action if necessary)
Area wipe tests – weekly
• An accurate area map must be drawn
and, on a weekly basis, a dry wipes
(filter paper or swab) are taken in each
area where radionuclides are used.
• The wipes are counted in a well counter
that uses open energy window. Also
background counts are obtained.
• Results of the counting procedure are
correlated with the area map. If greater
than 6600 dpm/cm2, notify the RSO
Leak test of sealed sources
 All sealed sources with half-life longer than
30 days (dose calibrator standards, well
counter calibration sources, spot markers,
etc.) must be wipe-tested before initial use
and then every 6 months.
 The results must be recorded in an
appropriate logbook.
 The test must be sensitive to 0.005 µCi.
Labeling and storage
of radionuclides
All containers, vials, syringes containing
radioactive material should be
• labeled properly
 With radiation symbols and words such as
CAUTION (or DANGER), RADIOACTIVE
MATERIALS
 Radionuclide
 Quantity of radioactivity and time/date measured
• Stored and shielded in secure area
• Constantly monitored when not secured
Labeling and storage of
radionuclides
• A syringe shield needs to be labeled if it
contains a syringe with radiopharmaceutical.
• Alternatively, it may have a transparent portion
to see the label.
Acceptable methods of waste
disposal
 Transfer to licensed person/company
 Decay in storage
 Release as effluents within authorized
limits (generally unnecessary)
Radioactive sharps disposal
• Use separate containers (e.g. sharps)
• Seal when full and label date and longest halflife
• 3 S’s: Sealed, Shielded, Secure location
• Before disposing, survey surfaces of container
to make sure not higher than the background
• Dispose of waste in appropriate containers
(e.g. biohazard but no radiation symbol)
Radioactive package receipt
• Must be inspected within 3 hours of
receiving or, if after hours, within 3 hours
of start of the next day
• Visually inspect the package for the DOT
radioactive material label, breakage, and
leakage
DOT package labeling
Surface exposure rate
(mR/hr)
Transportation index
White I
Yellow II
Yellow III
< 0.5
0.5-50
50-200
0
<1
1-10
Transportation index (TI) is the exposure rate
(mR/hr) measured at 1 meter from package.
DOT package labeling:
Radioactive I
0 at 1 meter
< 0.5 mR/h at surface
DOT package labeling:
Radioactive II
< 1 mR/h at 1 meter
< 50 mR/h at surface
DOT package labeling:
Radioactive III
< 10 mR/h at 1 meter
< 200 mR/h at surface
DOT radioactive placard for
the vehicle
Vehicles carrying packages bearing
Yellow III labels are required to post the
placard shown below on the outside of
the vehicle.
7
Radioactive package receipt
• Measure
exposure rates 1 meter from
package and at the surface
•If normal, proceed to wipe test
51
Exposure rate at 1 meter
Exposure rate at surface
Radioactive package receipt
• Wipe test
 Wipe area is about 300 cm2 on all sides.
 The counts should be less than 6600/min (22
dpm/cm2).
• If normal, remove the packing slip and open
the package.
• Complete entry in receipt log
• Store package in appropriate shielded area
54
Retention of records
20.2102 - Licensee shall maintain
records including:
…
ALARA
Efforts to reduce the radiation dose so long as
the expenditure does not overweigh the gain





Decrease of exposure time for workers
Increase of distance (inverse square)
Shielding (e.g. lead pigs), signs and labels
Personnel protection and monitoring
ALARA levels at GRU
• ALARA 1: 1.25 mSv in any given quarter
• ALARA II: 3.75 mSv in any given quarter
56
Protection from external
sources
• Time around a radiation source
• Distance from a radiation source
• Shield for syringes, vials and dose
calibrators, but usually not for walls
57
Photon intensity: inverse
square law
• Inverse square law used for
unshielded source, particularly useful
in PET
I = I0/d2
• Exposure rate (R/hr) = GA/d2
G: exposure rate constant for a point source
(Rcm2/(mCihr))
58
10 mCi F-18 radiation dose rate
Distance
0.5 m
1.0 m
1.5 m
2.0 m
2.5 m
3.0 m
3.5 m
4.0 m
Dose rate w/o lead
22.6 mrad/hr
6.3 mrad/hr
3.0 mrad/hr
1.4 mrad/hr
0.93 mrad/hr
0.62 mrad/hr
0.48 mrad/hr
0.39 mrad/hr
w 1/8” lead
13.6 mrad/hr
3.5 mrad/hr
1.6 mrad/hr
0.90 mrad/hr
0.54 mrad/hr
0.41 mrad/hr
0.29 mrad/hr
0.23 mrad/hr
30% increase in distance better than 1/8” lead shield
59
Photon intensity: exponential
attenuation
Exponential attenuation in a medium
I = I0 exp(-md)
• Reducing radiation using lead shield
60
Prevention against
ingestion/absorption/inha
lation of radioactivity
• No eating, drinking and applying
cosmetics in restricted areas
• Wearing lab coats and gloves
• Washing hands after handling
radioactivity
• Working with radioactive gases under
a ventilated fume hood
61
What is wrong?
No gloves, no syringe shield, no label, not
on counter with lead glass and absorber
What is wrong?
No lab coat, no gloves, no ring badge, no
syringe shield, no label, no absorber under
63
the injection spot, too happy perhaps?
Reportable medical events
• Diagnostic events resulting in a dose
that is
 Greater than 50 mSv effective dose, or
 Greater than 500 mSv dose equivalent to
any organ, or
 Greater than 500 mSv shallow dose
equivalent to skin
• Therapeutic events: administered dose
exceeds 20% of prescribed dose
Reportable medical events
• Dose equivalent to an embryo/fetus is higher
than 50 mSv, unless the dose is approved in
advance by the AU.
• Dose to a nursing child is higher than 50 mSv
or permanent damage to an organ or
physiologic system of the child.
• Events of patient intervention (intentional or
unintentional action, e.g. removing treatment
device) in which the dose may cause
permanent damage
Reportable medical events
• Must notify NRC/state, referring
physician and patient in writing, giving
pertinent details and plans for preventing
recurrence
• Mainly for radiotherapy not imaging
Agent
FDG (10 mCi)
Tc-mibi (20 mCi)
Tl (2 mCi)
EDE
7.0 mSv
7.0 mSv
12 mSv
Highest organ dose
59 mSv
29 mSv
46 mSv
66
Recordable but not reportable
events
Event resulting in a dose below the
NRC limits. It may caused by
• Administered dose falls 10% outside
the prescribed dose range, or
• Wrong patient, or
• Wrong radiopharmaceutical, or
• Wrong route of administration
• Need to be recorded locally and kept
67
for 10 years
Recordable but not reportable
events
• E.g. 10 mCi of In-111 octreotide is
66.7% more than the usually
prescribed dose of 6 mCi. This is a
recordable event for the hospital and
nuclear medicine department but
does not meet the NRC definition of
medical event.
What is major spill?
• Activity released at location or on
people
 100 mCi Tc-99m or Tl-201
 10 mCi Ga-67 or In-111
 1 mCi I-131
• Radiation safety officer must be
present.
• Focus on containment, shielding, and
decontaminating individuals
What to do with a major spill?
• Notify all persons in the area of spill
• Prevent spread of contamination




 Cover spill with disposable, absorbable
paper
 Remove contaminated clothing
Shield radioactivity if possible
Room sealed off
Report incident to RSO immediately
RSO directs further response.
70
What to do with a minor spill?
• Notify all persons in the area of spill
• Prevent spread of contamination
 Cover spill with disposable, absorbable
paper
 Remove contaminated clothing
• Clean up spill with disposable, absorbable paper
• Survey the area until the exposure rate is lower
than twice background level
• Personnel monitored (hands, shoes, clothing)
• Report incident to radiation safety officer
What is wrong?
No glove, no syringe shield, no label
72
What is wrong?
The hot lab
door is wide
open.