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

Example 4: Dental X‐ray room (BIR method)
An intra-oral dental X‐ray facility may require shielding from both primary and secondary radiation. The
primary beam should be intercepted by the patient, resulting in a transmission no greater than 2 μGy per film
(BIR, 2000). In this facility the distance from the wall to the nearest occupant in the adjoining surgery is 0.3
m, and the distance from the patient’s head/X‐ray tube head to the wall is 0.7 m. The weekly workload for
the X‐ray room is 100 intra-oral exposures.
Assuming 100% occupancy in the adjoining surgery what shielding is required in the common partition
wall
BIR advise that for intra-oral exposures the weighted average of primary plus scattered radiation dose at 1 m
is 1 μGy per film (BIR, 2000).
The annual dose constraint, D c
= 0.3 mSv
Occupancy, T, in adjoining surgery = 100%
Distance, d, from patient to occupant = 1.0 m
Average scatter dose per film at 1 m = 1 μGy
Weekly scatter based on 100 films = 100 μGy at 1 m
The incident kerma, K inc
= 100 μGy/week
= 0.1 mGy/week ≡ 0.1 mSv/week
Max. transmission, B =
K
inc
D
c
0.3 mSv
=
× T × 52 0.1 mSv × 1×
52
= 0.0577
From equation 5.6 for the transmission through lead, 0.2 mm lead will provide the shielding needed
at 70 kVp (see also Appendix C). In practice, Code 3 (1.32 mm) lead would provide adequate protection
and allow for increases in workload.
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The Design of Diagnostic Medical Facilities where Ionising Radiation is used