The Design of Diagnostic Medical Facilities where ... - ResearchGate

5.3.2 Nuclear medicine shielding calculation examples
Example 5: Shielding required for gamma camera room
A gamma camera room is adjacent to the reception area. 60 patients per week are scanned using a 99m Tc
bone scanning agent with an administered activity of 600 MBq. Patients are scanned two hours post
administration and scanning time per patient is 30 minutes. The distance from the patient to a person in the
adjoining office is 3 m.
What shielding is required for the wall between the camera room and the reception
The dose from a single patient at the point of interest is given by equation 5.7:
F
D(t) = D(0)
.
× t × R
t
×
d
where Ḋ(0) is the product of the dose rate constant for the patient, having been administered 99m Tc and
the activity administered (MBq), t is the scanning time, and F u
and R t
are the decay factor prior to
scanning and the dose reduction factor during scanning respectively.
u
2
For a workload of N w
patients per week, the annual dose at a distance d from the patient is:
.
F
D(t
a)
= N
w
× 52×
D(0) × t × R
t
×
d
Values for the dose rate constant for the patient administered 99m Tc , R t
and F u
are given in Section 5.2.8
as 0.0075 μSv m 2 /MBqh, 0.97 and 0.79.
u
2
Thus:
D(t a
) = 60 x 52 x 0.0075 μSv m 2 /MBqh x 600 MBq x 0.5 h x 0.97 x
= 598 μSv = 0.598 mSv
0.79
9
For an occupancy factor of 1.0, and a dose constraint of 0.3 mSv, the transmission is
0.3 mSv
B =
= 0.50
0.598 mSv × 1
To reduce the transmission to 50%, one half value layer of shielding is required. From Appendix D,
0.3 mm of lead will provide adequate shielding.
The Design of Diagnostic Medical Facilities where Ionising Radiation is used 71