Shielding and layout

1. Planning of Nuclear Medicine Facilities
Shantanu Mishra
Medical Physicist (RSO)
Dept. of Radiation Oncology
Dr. B Borooah Cancer Institute

2. What is Nuclear Medicine?
Nuclear medicine is a medical specialty involving the
application of radioactive sources in open form for the
diagnosis and treatment of disease.
• uses relatively small amounts of suitable radioactive materials for
diagnosis (e.g.~5-80 mCi of Tc-99m) and treatment (e.g.~60- 300 mCi
of I-131)
• Radiopharmaceutical is the pharmaceutical labeled with radioisotope
• Radiopharmaceuticals substances are localized in specific organs,
bones, or tissues
• Gamma photons emitted from the patient can be detected externally
by special types of scanners e.g. Gamma or PET cameras.
• Cameras work in conjunction with computers to form images that
provide data and information about the area of body being imaged

3. Applications of Nuclear Medicine
Common Nuclear Medicine applications which include:
diagnosis and treatment of hyperthyroidism
cardiac stress tests to analyze heart function
bone scans for metastatic growths
lung scans for blood clots
kidney, liver and gall bladder procedures to diagnose abnormal
function or blockages.

4. Radiopharmaceuticals Most Commonly Used
• The main radionuclide used for diagnostic Nuclear Medicine
procedures is technetium-99m (99mTc). Others are I-131 &Tl-
201
• The main radionuclide used for therapeutic Nuclear Medicine
procedures is Iodine-131 (131I). Others are P-32, Sr-89, Sm-153
and Rh-186.

5. Technetium-99m
• Tc-99m radionuclide is daughter product of Mo-99 radionuclide
99Mo T1/2 (67 hrs) 99mTc T1/2 (6 hrs) 99Tc + 140 keV Gamma
• ß –decay Isomeric decay

6. PET isotope
PET-Radioisotope:
PET radioisotopes are proton rich nuclides positron
annihilates with electron resulting two photons of energy
511 keV each emitted in opposite directions
i.e. Positron + electron = two gamma photons of energy
511 keV each

7. Physical characteristics of PET radioisotopes
Radioisotope Half life Gamma Energy
F-18 110 min 511 keV
O-15 20 min 511 keV
N-13 10 min 511 keV
C-11 2 min 511 keV

8. Therapeutic Applications in Nuclear Medicine
• High Dose Therapy in Nuclear Medicine:
Beta emitting radioisotopes ( I-131 and P-32 etc.) of activity ranging from 60
to 300 mCi is administered into patient body with suitable pharmaceutical
(Radiopharmaceuticals). Patient is admitted into isolated wards
I-131 is used for treatment of thyroid diseases whereas P-32 is used for
palliative treatment of bone.
o Low Dose Therapy in Nuclear Medicine: Activity range is 10-30 mCi
oPatient is discharged only after activity reduces to acceptable limit as
prescribed by the regulatory body (5 mR/h at 1 m from the patient).

9. Radioimmunoassay (RIA)in Nuclear Medicine
•
Radio-immuno Assay RIA) procedures:
RIA is a In - vitro Procedures where no radioactivity is injected
into patient’s body.
o RIA is a very sensitive method to evaluate the hormone levels in
blood serum.
oI-125 (half life 60 days, 35 keV gamma photon/EC energy is
mostly used for RIA application

10. Physical characteristics of commonly used
radioisotopes in Nuclear Medicine
Radioisotope Half life Gamma Energy Beta Energy (Max.)
Tc-99m 6 hrs 140 keV --
I-131 8.4 days 364 keV 610 keV
I-125 60 days 35 keV --
P-32 14.6 days -- 3.2 MeV

11. Equipments used in Nuclear Medicine for
Imaging
Most commonly equipment used for imaging in NM are:
• Gamma Camera
• SPECT
• PET

12. Equipments used in Nuclear Medicine for
Imaging
Most commonly equipment used for imaging in NM are:
• Gamma Camera
• SPECT
• PET or PET-CT

13. Typical Layout of NM facility with Gamma
Camera/SPECT

14. Typical Layout of NM facility with PET/CT

15. Typical Layout Plan of NM facilities having both
SPECT and PET-CT
Fig: Typical Layout Plan of NM facilities having Gamma Camera and PET facilities

16. Typical Layout Plan High Dose Therapy

17. Delay tank

18. Shielding Calculations of NM Facilities
Shielding calculation of following facilities
1. Gamma Camera/SPECT
2. High Dose Therapy
3. PET Installation
4. Hot Lab
5. Uptake room

19. Shielding Calculations of NM Facilities contd..
FACTORS AFFECTING SHIEDLING REQUIREMENTS:
• Radionuclide –Half life, emissions
• Procedure protocol –Administered activity, uptake time, scan time
• Dose rate from the patient –Dose constants, patient attenuation, decay, number of
patients per week.
• Facility layout –Controlled vs uncontrolled areas, occupancy factors, detection
instrumentation
• Regulatory Limits

20. Factors affecting dose rate from patients:
• Dose rate - The appropriate dose rate constant for F-18 for shielding purposes is
0.143 μSv m2 /MBq h, and the dose rate associated with 37 MBq (1 mCi) of F-18 is
5.3 μ Sv/ h at 1 m from an unshielded point source. For Tc-99m : 0.033 μSv m2 /MBq
h
Shielding Calculations of NM Facilities
contd..

21. • Because PET tracers have short half-lives, the Total radiation dose received over a time
period t, D(t), is less than the product of the initial dose rate and time [Ḋ(0) × t ].
The reduction factor, Rt, is calculated as:
Rt = D(t) [Ḋ(0) × t ]
=
Where, D(t) is Total dose for time t (μSv)
Ḋ(0) is Initial dose rate (μSv/ h)
For F-18, this corresponds to Rt factors of 0.91, 0.83, and 0.76 for t= 30, 60, and 90 min,
respectively.
For Tc-99m, Rt factor for 60 min is 0.97 .
Uptake time
Patients undergoing PET/SPECT scans need to be kept in a quiet resting state prior to imaging
to reduce uptake in the skeletal muscles. This uptake time varies from clinic to clinic, but is
usually in the range of 30– 90 min.
1.44 x (T1/2 t) x [1 - 𝑒
(0.693𝑡 T1/2
)
]

22. Shielding Calculations of NM Facilities contd..
1.Gamma Camera/SPECT:
Room size normally ~5mx6m
In Gamma camera, normally Tc-99m is used for imaging purpose (dose rate constant= 0.12 R/hr-Ci at 1m)
a) Uptake room:
Workload (W):
The dose D(t) from a single patient at 1 m = D (0) × tu × Rt
D (0) is product of dose rate constant and activity administered initially, tu is uptake time; and Rt is dose reduction
factor {=D(t)/[Ḋ(0) × t] = 1.44 × (T1/2/tu) × [1-exp(0.693 t/T1/2)]
W= No. of patient imaged per week (120) × D(t) mR/wk at 1m = 120 × Ḋ(0) × tu × Rt mR/wk at 1m
= 120 × 10 mCi × 0.12 R/hr-Ci × 0.5 hr × 0.97 = 69.8 mR/wk at 1m
RF= WUT/Pd2= 69.8 × 1 × 1/ 2 ×(2.5+.23)2 =4.683 (P= 1mSv/yr for general public)
Thickness=Log RF x TVT value= 0.671 x 4.45 cm of concrete=2.984 cm concrete
Note: In general 9” brick or 6” concrete is adequate shielding for all imaging modalities except PET
facility.

23. Shielding Calculations of NM Facilities
contd..
b) Shielding for Gamma Camera/SPECT imaging room:
Because of the delay required by the uptake phase between the administration of
the radiopharmaceutical and the actual imaging, the activity in the patient is
decreased by FU
Fu is decay factor of administered activity[= exp (-0.693 × tu/T1/2]
where tU is the Uptake time
In most cases the patient will void prior to imaging, removing approximately 15%
of the administered activity and thereby decreasing the dose rate by 0.85.

24. Shielding Calculations of NM Facilities
contd..
b) Shielding for Gamma Camera/SPECT imaging room:
Total workload (W);
The dose D(t) from a single patient at 1 m = D(0) x tu x Rt x Fu x .85
D (0) is product of exposure rate constant and activity administered initially, t is uptake time; and
Rt is dose reduction factor
Fu is decay factor of administered activity
W= No. of patient imaged per week (120) × D(t) mR/wk at 1m
= 120 × D(0) × tU x Rt × .85 mR/wk at 1m
= 120 × 10 mCi × 0.12 R/hr-Ci × 0.5 hr × 0.97 (dose reduction factor) × 0.85 (void corr.)
= 59.3 mR/wk at 1m
RF= WUT/Pd2= (59.3 × 1 × 1)/2 × (2.5+.23)2 =3.98
Thickness=Log RF x TVT value= 0.60 × 4.45 cm of concrete=2.67 cm concrete
Note: In general 9” brick or 6” concrete is adequate shielding for all imaging modalities except PET
facility.

25. Shielding Calculations of High Dose Therapy facility
2. High Dose Therapy:
 I1-31 is used for high dose therapy ( Thyroid ablation) and activity range varies
from 50-300 mCi.
 Patient administered with activity is admitted in an isolation ward in the hospital
 Patient is discharged from the hospital only after radiation level comes down
below the regulatory limit (5mR/h at 1 m from the patient)
 There is an active toilet in the isolation ward whose outlet is connected to the delay
tank
 Activity is discharged into the sewage system once activity concentration comes
down below the regulatory discharge limit (22 MBq/m3).
Therefore, radiation shielding calculation of Isolation ward is necessary

26. Shielding Calculations of High Dose Therapy
facility contd.
Shielding calculation of High Dose Therapy (300 mCi of I-131 per isolation
ward):
Workload (W) = г (R/h-Ci) × A (Ci) at 1 m = ____R/h at 1 m
W = 0.22 × 0.3=66 mR/week at 1m
U=1, T=1, P=2 mR/wk, d=2.5+0.23 =2.73 m (room dimension ~5x6 m2)
RF=WUT/Pd2 = 66 × 1 × 1/ (2 × 2.73)2 = 4.43
No. of TVLs (n)= Log[RF]=0.646
Thickness= n x TVL value of concrete for I-131=0.646 x 9.9 cm=6.395 cm of concrete
Note: In general thickness is given 6” concrete or 9’ brick

27. Shielding Calculations of PET
facility
Patient Dose rate Constant
• Unshielded 18F source constant is 0.143μSv-m2/MBq-h
• Body absorbs some of the annihilation radiation, the dose rate from the
patient is reduced by a significant factor.
• TaskGroup-108 recommends using 0.092μSv-m2/MBq-h immediately
after administration.
• D(0)=0.092 × 10-6 × 100 / (0.027 × 10-3 ) R/Ci-h = 0.34 R/Ci-h

28. Shielding Calculations of PET
facility
Radioactive decay
• Because PET tracers have short half-lives, the total radiation dose received
over a time period t, Dt˂Ḋ(0)× t. The reduction factor of dose, Rt, is
calculated as Rt= Dt/ Ḋ(0)× t = 1.443 (T1/2/t) × [1 − exp− 0.693 × t/T1/2]
For F-18, this corresponds to Rt factors of 0.91, 0.83and 0.76 for t=30, 60,
and 90 min, respectively

29. Shielding Calculations of NM Facilities contd..
PET facility:
Room size normally ~5mx6m;In PET facility normally F-18 PET radioisotope is used for imaging purpose
a)Uptake room: Workload (W)
The dose D(t)from a single patient at 1 m = D(0) x tu x Rt,U
D(0) is product of dose rate constant and activity administered initially, tu is uptake time; and Rt,u is dose
reduction factor {=D(t)/[D(0) x t]=1.44 x(T1/2/tu)x [1-exp(0.693 tu/T1/2]},
W= No. of patient imaged per week (120) x D(t) mR/wk at 1m= 120x D(0) x tu x Rt,U mR/wk at 1m
= 120x 10 mCi x 0.34 R/hr-Ci x 0.5 hr x 0.91 (for 30 min) = 185.6 mR/wk at 1m
RF= WUT/Pd2= 185.6x1x1/2x(2.5+.23)2 =12.452
Thickness=Log RF x TVT value= 1.095 x 15 cm of concrete=16.428 cm concrete
=Note: In general 9” concrete is in PET facility.

30. Shielding Calculations of NM Facilities contd..
b) Shielding for PET imaging room:
Total workload (W);
The dose D(t)from a single patient at 1 m = D(0) x t x Rt xFu x .85
D(0) is product of exposure rate constant and activity administered initially, t is uptake time; and
Rt is dose reduction factor=D(t)/[D(0) x t]=1.44 x(T1/2 /t) x [1-exp(0.693 t/T1/2]
Fu is decay correction factor=exp-(0.693 x tu/T1/2)= exp-0.693 x 60 /110 = 0.68 [for F-18 ; at 1h]
Factor 0.85 is to account for patient voiding before scanning;
W= No. of patient imaged per week (120) x D(t) mR/wk at 1m= 120 x D(0) x t x Rt x 0.68x 0.85 mR/wk at 1m
= 120 pt/wk x 10 mCi x 0.34 R/hr-Ci at 1m x 0.5 hr x 0.91 (dose reduction factor) x .68x0.85) = 107.3 mR/wk at 1m
RF= WUT/Pd2= 107.3x1x1/2x(2.5+.23)2 =7.199
Thickness=Log RF x TVT value= 0.857 x 15.0 cm of concrete=12.86 cm concrete
Note: In general 9” brick or 6” concrete is adequate shielding for all imaging modalities except PET
facility.

31. Calculation for above and below PET facility

32. Transmission data