Contents
• Safety
Safety, Site Planning and
Shielding
g
–
–
–
–
Patients
Personnel
Public
Equipment
• Site Planning
– Source flows
– Work flow
– Adjacencies
• Shielding
Richard E. Wendt III,
Nancy Swanston and William D. Erwin
Department of Imaging Physics
UT M. D. Anderson Cancer Center
– Localized
– Structural
Common PET Radionuclides
Nuclide
Δ(β ++
γ±)/
Δ(total)
Δ(total)/Abundance(γ±) ×10-13
Mean Life
(min)
Avg. Life/
Scan time
F-18
Dose Rate
Constant
C-11
1.003
1.123
29.42
0.98
0.148
N-13
0.999
1.212
14.38
0.48
0.148
O-15
0.996
1.049
2.94
0.10
0.148
F-18
1.000
1.049
158.40
5.28
0.143
Cu 62
Cu-62
0 993
0.993
1 886
1.886
14 05
14.05
0 47
0.47
Cu-64
0.742
1.404
1099.65
36.66
0.029
Ga-68
0.983
1.511
98.21
3.27
0.134
Rb-82
0.952
2.097
1.88
0.06
0.159
I-124
0.332
4.416
8685.71
289.52
0.185
Δ(β++ γ±)/Δ(total) : Energy released by “useful” positrons and annihilation photons over total energy released. Data from
MIRD Decay Schemes (Δ in Gy-kg/Bq-s).
Abundance of annihilation photons from Lund NuDat database: http://nucleardata.nuclear.lu.se/Database/Nudat/.
External effective dose equivalent dose rate constants from TG108 (μSv-m2/MBq-hr).
A scanning time of 30 minutes is assumed.
K.F. Eckerman & A. Endo, MIRD Radionuclide Data and Decay Schemes, 2nd Ed., Reston:
Society of Nuclear Medicine, 2008.
1
I-124
Useful Energy/Total Energy
Useful Energy/T
Total Energy
1.2
1.0
0.8
0.6
0.4
0.2
0.0
C-11
N-13
O-15
F-18
Cu-62
Cu-64
Ga-68
Rb-82
I-124
Radionuclide
K.F. Eckerman & A. Endo, MIRD Radionuclide Data and Decay Schemes, 2nd Ed., Reston:
Society of Nuclear Medicine, 2008.
Dose Rate Constants
Energy per Annihilation Photon
0.2
5.00
0.18
Dose Rate Constant (uS
Sv-m^2/MBq-hr)
Energy/Annihilation Ph
hoton (100 fJ)
4.50
4.00
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
0.00
C-11
N-13
O-15
F-18
Cu-62
Radionuclide
Cu-64
Ga-68
Rb-82
I-124
C-11
N-13
O-15
F-18
Cu-64
Ga-68
Rb-82
I-124
Radionuclide
2
Patient Absorbed Doses
Average Lifetime
Organ Absorbed Doses (mGy)
4.00
Dosage
MBq
EDE
mSv
F-18 FDG
370
11.1
GB Wall
F-18 NaF
185
5.0
LLI Wall
Rb-82
4440
5.34
30
195
Tc-99m MDP
1110
6.77
Tc-99m MIBI
1110
16.6
15
1.78
Dx AC CT
WB
13.6
Res. AC CT
WB
5.9
0
20
40
60
80
Radiopharmaceutical
100
Adrenals
3.50
Brain
SI
I-124 NaI
Stomach
2.50
ULI Wall
Heart Wall
2.00
MIRD Target Organ
Log Average Lifettime (min)
Breasts
3.00
1.50
1.00
Kidneys
Liver
F-18 FDG
Lungs
I-123
F-18 NaF
Muscle
Rb-82
I-124 NaI
Ovaries
Pancreas
Red Marrow
Bone Surf
0.50
Skin
Spleen
Testes
0.00
C-11
N-13
O-15
F-18
Cu-62
Cu-64
Ga-68
Rb-82
I-124
Radionuclide
Thymus
I-124 Thyroid
630 mGy
Thyroid
UB Wall
CT data from Donna Stevens, M.S.
and Tinsu Pan, Ph.D.
Uterus
Controlling Personnel Doses
• Time
– Plan workflow to administer activity after other
things are taken care of
– Be efficient and share high dose duties
• Distance
– Use remote monitoring
• Shielding
– Syringe shields and injection systems
– Structural shielding
Radiopharmaceutical data from tables
in M.G. Stabin, et al., Radiation Dose
Estimates for Radiopharmaceuticals,
Oak Ridge Institute for Science and
Education, 30 April 1996,
NUREG/CR-6345, and from typical
administered activities.
Exposure in PET Clinic
Operations
• Radiopharmaceuticals
– Receipt
– Disposal
– Storage
• Patient Contact
–
–
–
–
–
–
–
Consultation
Injections
Positioning
Foley Catheters
Care for the Claustrophobic Patient
Pediatric Population
Evaluation of Sedation
3
Syringe Shields
Gaard Lock
88% atten
Z-PET
UT MDACC based on
Cardinal Health’s
→100% atten
97% atten
Manual Injector (Biodex)
Angel Shield Injector
(Pinestar)
Infusion System
(MEDRAD)
PET Dose Assay Station
2” Pb
Delivery of Unit Doses
Exposure Rate (20 mCi 18F)
4” Pb glass
~ 6 cm
~ 1.25 cm
2” Pb L-block
~ 73 R/h
~ 3.2 R/h
~ 18 cm
6 cm Pb rings
~ 0.35 R/h
4
1-Year PET Exposure Study
• PET Technologist
PET Technologist: Source of Exposure
• average daily volume = 12 patients
<1
Positioning 3 patients
• data was collected over gestation period
• duties were modified to decrease amount of time
spent with radioactive sources (limiting injections of
18FDG, patient positioning, survey/wipe of
radiopharmaceutical shipments)
• Injection Personnel (Nurses)
• data collection was recorded for two months
• 275 injections with and without tungsten syringe
shields
1-Year PET Exposure Study
534
mrem
Technologist daily
2
mrem
Pregnant technologist gestation
43
mrem
Pregnant technologist daily
0.2 - 0.3
mrem
Injection personnel annual
1040 - 2600
mrem
Injecting personnel
mrem
Wipe & delivery of PET isotopes
• Pregnant PET Technologist
Technologist annual
1-Year PET Exposure Study
4 - 10
mrem/day
™ with tungsten syringe shield
0.02 - 0.035
mrem/mCi
™ without tungsten syringe shield
0.036 - 0.06
mrem/mCi
1
Manipulation of urinary catheter
<3
Assistance with sedated patients
<7
Consultation with injected patients (time spent < 10 min.)
™ 0 – 90 min. post injection
1
™ 90 – 180 min. post injection
<1
Note: 15 – 20 mCi 18FDG as injected dose
Fiscal Year 2006 Evaluation
Dose Monitoring
Daily Exposure Averages FY06
PETCT Trainee
PET Technologist
PET Pharmacy Technologist
PET Supervisor
Pregnant PETCT Technologist
mR
3.9
2.8
1.5
1.1
0.33
Gestation
to Date
(mR)
Weeks
na
na
na
na
na
na
22
16
32
32
5
Patient Positioning Personnel
Exposure Study
Patient Positioning Personnel
Exposure Study
Measurement Method
• Average measured exposure = 2.33 mR (0.023 mSv)
• Calculation = 2.24 mR (0.022 mSv)
• Exposure not strongly correlated w/ patient BMI
Exposure vs. Body Mass Index
1000
900
800
To tal exp osu re (m R )
• Calibrated Inovision 451B Ion Chamber Survey
Meter
• 5 minute
i t exposure reading
di
• 20 cm from the abdomen
• 40 patients post-void
• Average 18FDG dose = 17.82 mCi (660 MBq)
• Average uptake time = 86.7 minutes
700
600
500
y = -10.041x + 994.12
R 2 = 0.1697
400
300
200
100
0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
BMI (kg/m 2)
PET Nurse Finger Badge Readings*
Skin Limit (mrem): 12500/quarter
Extremity Limit (mrem): 12500/quarter
Site Planning
50000 Annual
50000 Annual
Nurse
A
B
C
D
E
F
G
H
mrem
Apr-Jun Jul-Sep Oct-Dec Apr-Dec Max.
2480
1920
1720
6120
2480
1340
790
360
2490
1340
3900
730
1480
6110
3900
1630
1620
1370
4620
1630
2490
1650
560
4700
2490
1750
2620
1760
6130
2620
210
94
1280
1584
1280
1000
2180
3180
2180
Overall Max.:
3900/quarter
Nurse
A
B
C
D
E
F
G
H
mrem per patient
Apr-Jun Jul-Sep Oct-Dec Apr-Dec
4.81
6.47
6.99
5.69
7.05
3.24
2.78
4.33
12.18
3.17
4.38
6.75
10.76
7.45
4.80
6.74
8.29
6.17
2.37
5.23
7.92
12.38
6.73
8.56
2.44
0.97
6.51
2.51
13.51
6.71
5.74
Overall:
Min.
4.81
2.78
3.17
4.80
2.37
6.73
0.97
6.71
0.97
Max.
6.99
7.05
12.18
10.76
8.29
12.38
6.51
13.51
13.51
• Layout
– Flow of Patients
– Flow of Other Sources
– Flow of Personnel
• Proximity of Other Instruments
• Proximity of Uncontrolled Space
• Future Proofing
* Apr-Dec ’05 Courtesy Shannon Worchesik, PET Nursing Supervisor, UTMDACC
6
Uptake Rooms
Adjacencies
• For F-18 FDG imaging, two or three uptake
rooms are needed to support a single scanner.
• As scanners become more efficient, this number
will increase since the uptake time for FDG will
g
not change.
• Uptake rooms should be quiet and dark.
• Remote monitoring via CCTV, intercoms or
mirrors is desirable.
• Uptake rooms should be shielded to protect
personnel working with a patient prior to
injection.
• Nuclear medicine equipment including
gamma cameras and well counters should
be protected from PET by shielding or
distance.
• PET patients should have a dedicated
toilet that does not require their walking
near sensitive instruments.
• Assume the worst for adjacent areas not
under the licensee’s control.
Future Proofing
Unshielded Dose Rates
• We have seen a steady growth in FDG
PET/CT which justifies our having shielded
to worst case workloads.
• Envisioning
g future g
growth as well as
possible changes in the use of adjacent
space can avoid costly retrofitting.
• It is desirable to have a physics lab,
shielded if necessary, where phantoms
may be prepared and later stored for
decay.
• 20 μSv/hr (2 mrem/hr) is the dose rate from an
unshielded point source of F-18 at
–
–
–
–
1 cm from 14 kBq (378 μCi)
10 cm from 1.4 MBq (37.8 μCi)
1 m from 140 Mbq (3.78 mCi)
2 m from 559 Mbq (15.1 mCi)
• Since PET sources are relatively steady, the “2
mrem in any one hour” rule is usually covered by
the weekly limits.
• CT could be an issue if PET protection is
afforded mainly by distance, rather than
shielding.
7
Weekly Limits
• We shield public areas to 2 mrem/wk (20
μSv/wk) and controlled areas to 10
mrem/wk (100 μSv/wk).
• The actual public exposure is practically
much lower because most public areas
are well below 20 μSv/wk when the worst
spots are at 20 μSv/wk.
Shielding
• Structural shielding is typically necessary
for clinical PET facilities.
• AAPM Task Group 108 Report and
several talks from the AAPM Summer
School 2007 address shielding in greater
detail than we can here.
• A neglected area is the shielding offered
by the PET/CT instrument itself.
Occupancy Factors
• NCRP 147 gives modern occupancy factor
recommendations.
• Fractional occupancy factors make sense
for p
public areas.
• NCRP 49 clearly states that unity
occupancy factors should be used in
controlled areas.
• The example in TG108 has T=0.25 for a
controlled corridor.
F-18 Shielding by the Patient
• TG108 recommends assuming 36% absorption
by the patient based upon an analysis of
published external measurements of patients.
• TG108 sanity checks this with the MIRD whole
body absorbed fraction (MIRD Pamphlet 5
5,
revised – 34% for 500 keV photons).
• Using the penetrating and non-penetrating
energies in the MIRD decay scheme and the 70
kg WB S-value from the Olinda software for F-18
gives 30% absorption of photons.
8
Estimated Shielding by the Patient
TG108 Shielding - Lead
Penetrating Radiation WB Absorption Fractions
0.35
0.32
0.31
0.33
0.30
0.30
0.30
0.30
0.5
0.30
0.27
0.27
0.25
0.20
0.15
0.10
0.05
0.00
C-11
N-13
O-15
F-18
Cu-62
Cu-64
Ga-68
Rb-82
I-124
Mean: 0.30, Maximum: 0.33, Minimum: 0.27. Note that this approach is more
conservative than TG108 for F-18.
M.T. Madsen, et al., “Task Group 108: PET and PET/CT Shielding Requirements,” Medical Physics, 33(1):4-15, 2006, Fig. 1
TG108 Shielding - Concrete
TG108 Shielding - Iron
0.5
M.T. Madsen, et al., “Task Group 108: PET and PET/CT Shielding Requirements,” Medical Physics, 33(1):4-15, 2006, Fig. 2
M.T. Madsen, et al., “Task Group 108: PET and PET/CT Shielding Requirements,” Medical Physics, 33(1):4-15, 2006, Fig. 3
9
TG 108 Shielding Approach
TG 108 Shielding Approach
• Calculate a “reduction factor,” Rt, that
converts the initial activity or dose rate at
the start of a interval to the average
quantity during that interval
interval.
• Calculate the weekly dose using the
patient-shielded initial activity, the duration
of the event, the number of events a week,
and the dose reduction factor.
• Calculate the required transmission factor
of a barrier by incorporating the occupancy
factor and the weekly dose limit.
• Convert the transmission factor to a
thickness of a particular material using the
Monte Carlo simulation results in Table IV
or the fits of the Archer equations to them.
What is a Source?
Source Locations
• A “source” is activity at a particular location.
• The source comprises numerous different
physical entities that occupy that location during
the course of the week.
• An individual patient contributes to the source in
the uptake room, the source in the toilet, the
source in the scanner room, the source in the
dressing room, and perhaps the source in the
waiting room over the course of his or her study.
10
Uptake Room Calculation
Rt =
D (t )
D& (0) × t
= 1.443 ×
D(tU ) =
Rt = 1.443 ×
T1 2
t
× [1 − e
−
0.693t
T1 2
]
μSv - m 2
0.092
× A0 MBq × tU hr × RtU
MBq - hr
d m2
Note that D(t) is the cumulative dose from time zero to time t, not the
dose rate at time t. The dose rate constant 0.092 for F-18 includes the
self-shielding afforded by the patient (i.e., it is 64% of 0.1443).
Uptake Room Calculation
B=
Uptake Room Calculation
−
109.8
× [1 − e
60
0.092
D(60 min uptake) =
=
D(60 min, 3 m) =
0.693×60
109.8 ] =
0.832
μSv - m 2
× 370 MBq × 1.0 hr × 0.832
MBq - hr
d m2
28.3 μSv - m 2
d m2
28.3 μSv - m 2
9 m2
= 3.14 μSv
Multiple Sources
P
T × N w × D(tU )
20 μSv/wk
at 3 m
1 0 × 33 pts/wk × 3.14 μSv/pt
1.0
= 0.193 at 3 m
=
Look up B = 0.193 in Table IV of TG108 to determine that
this degree of attenuation requires about 10 mm of lead,
15 cm of concrete or 4.5 cm of iron.
A point is irradiated by multiple sources at different distance through
various amounts of shielding.
11
Color Coding
50.7
1.9 0.98 mrem/wk
5.4
11.7
Unshielded Exposure
3
1.3
Exposure (or EDE) =
Γ × Activity
r2
μ Sv - m 2
R − cm 2
Γ→
or
mCi − hr
MBq - hr
Exposure Control Zones
PET/CT Installation
Not shown: Public area in next building 50 feet to the north.
Equipment
10 mrem/wk
T=0.025
MR Offices
2 mrem/wk
T=1
St i
Stairs
2 mrem/wk
T=0.025
Tech
6 mrem/wk
T=1
Technical Corridor
10 mrem/wk
T=1
Nursing
8 mrem/wk
T=1
Future Office?
2 mrem/wk
T=1
Public Corridor
2 mrem/wk
T=0.125
Offices and Labs
2 mrem/wk
T=1
12
Exposure Control Zones
Barriers
Unzoned
Zoned
10 mrem/wk, T=1
10 mrem/wk
2 mrem/wk
2”
1”
3/4”
1/2”
1/4”
2 mrem/wk, T=1
1/8”
100 mrem/wk, T=1
Zoned Exposure
Testing
The collimating effect of holes in thick lead
makes radionuclide leak testing difficult (and
largely impractical for general surveys) but does
help to ensure that small, undetected leaks
have minimal effect. We like to perform a leak
test with visible light prior during construction.
13
Wall Systems
Uptake Rooms Floor
Scan Room Floor
Scan Room Ceiling
14
Scan Room Wall
Scan Room Wall
Uptake Rooms Walls
Penetrations
15
Penetrations
Resources
• M.T. Madsen, et al., “AAPM Task Group 108: PET and PET/CT
Shielding Requirements,” Medical Physics, 33(1):4-15, 2006,
http://www.aapm.org/pubs/reports/RPT_108.pdf
• W.S. Snyder, et al., MIRD Pamplet 5, Revised, 1978,
http://interactive.snm.org/docs/MIRD%20Pamphlet%205.pdf
• M.G. Stabin, et al., Radiation Dose Estimates for
Radiopharmaceuticals, Oak Ridge Institute for Science and
p 1996,, NUREG/CR-6345,,
Education,, 30 April
http://www.nrc.gov/reading-rm/doccollections/nuregs/contract/cr6345/
• AAPM Summer School 2007, various shielding talks,
http://www.aapm.org/meetings/07SS/
• R.L Metzger, “Shielding Design for PET Clinics,” HPS Midyear
Symposium, 2006,
http://www.radsafe.com/documents/PETshieldHPS.ppt, accessed
June 2008.
• K.F. Eckerman & A. Endo, MIRD Radionuclide Data and Decay
Schemes, 2nd Ed., Reston: Society of Nuclear Medicine, 2008
16