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

Example 3: X‐ray room window (BIR method)
The general radiographic room is located on the first floor. There is a window in the external wall, which is
at a height much greater than 2 m from the outside ground. The distance from the patient table to the
window is 2 m. An occupant works at the window of an office across the courtyard at a distance of 8 m from
the window of the X-ray room.
The weekly workload for the room has been obtained from the Radiology Information System (RIS) and
found to be 1000 Gy cm 2 for 300 examinations, with an average X‐ray beam energy of 100 kVp.
What shielding is required for this window
There is no vertical bucky in the room and lateral exposures will not be directed towards the window in this
instance, so only scattered radiation needs to be considered.
The annual dose constraint, D c
= 0.3 mSv
Occupancy in office across courtyard, T = 100%
Distance from patient on table to
occupant in the office, d
= 10 m
Average weekly DAP = 1000 Gy cm 2
Scatter factor at 1 m, S max
= [(0.031 x kVp) + 2.5] μGy (Gy cm 2 ) -1 (Equation 5.3)
= 5.6 μGy (Gy cm 2 ) -1
The incident kerma,
S
max
× DAP
K
inc
=
d
2
(Equation 5.4)
5.6×
1000
= 56μGy = 0.056 mGy ≡ 0.056 mSv
10
K
inc
=
2
Max. transmission,
B
=
K
inc
D
c
× T × 52
= 0.3 mSv
0.056 mSv × 1×
52
= 0.1030
From equation 5.6 for the transmission through lead and concrete, 0.3 mm lead or 26 mm concrete is
needed to shield the window (see also Appendix C) (neglecting any attenuation in the glass
window).
Window shielding is therefore required in this room even though the window is located at a height of
greater than 2 m from the outside ground. Shielding may be provided as outlined in Section 6.3.4.
Should there be a requirement to direct lateral exposures towards the window then the shielding
requirement will be increased.
If there are two adjacent X‐ray rooms with external windows facing into the courtyard then the
combined effect of both rooms on the office will have to be considered.
The Design of Diagnostic Medical Facilities where Ionising Radiation is used 69