1. Example Outside (Car Park and seating) Wall A 4.2m 1.3m Wall D Wall B
Waiting Area (not attended)
1.1m
Offices
3.8m
Operator Area
Wall C
Distance to ceiling from table – 2m
Offices on floor above
Corridor
not drawn to scale

2. Example – Exposure Details
Only two investigations in this room
AP Abdomen (patient supine on table)
DAP – 6.5 Gy.cm2
30 examinations per day
AP Pelvis (patient supine on table)
DAP – 5.5 Gy.cm2
20 examinations per day
All exposures at 100 kV
Room in use 5 days per week, 52 weeks per year

3. Calculation required
Thickness of lead required to shield walls adequately (specify as lead code).
Thickness of concrete required to shield ceiling adequately.
(note, this is a ground floor room with no basement)
Assuming a dose constraint (Dc ) of 0.3mSv per annum

4. X-ray transmission through lead

5. X-ray transmission through concrete

6. Coefficients for empirical formula at 100 kV
Material
Lead
2.5
15.28
0.756
Concrete
0.0395
0.0844
0.519

7. Solution Total DAP per annum for Abdomen
48750 Gy.cm2
6.25 Gy.cm2 x 30 per week x 5 days per week x 52 weeks
Total DAP per annum for Pelvis
28600 Gy.cm2 (5.5 x 20 x 5 x 52)
Scatter factor at 100 kV
[(0.031 x 100) + 2.5] = 5.6 mGy.(Gy.cm2)-1
Scatter in room at 1m
5.6 x ( ) = mGy per annum
ie mGy per annum

8. Transmission Distance (m) Annual scatter (mGy) Kinc*52 Occupancy T
(x10-3) B
Wall A
1.3
256.3
0.1
11.7
Wall B
2.1
98.2 1
3.05
Wall C
2.5
69.3
0.2
21.6
Wall D
0.05
61.1
Operator area
1.1
358.0
0.84
Ceiling
2.0
108.3
2.77
inverse square law corrected

9. ( ) ú û ù ê ë é + = a b ag 1 ln B x Shielding required - g Lead (mm)
Lead code
Concrete (mm)
Wall A
0.84 3 66
Wall B
1.32
3/4 96
Wall C
0.65 54
Wall D
0.37 35
Operator area
1.81 5
126
Ceiling
1.35 4 98 ( ) ú û ù ê ë é + = - a b ag g 1 ln B x

10. Notes on the solution
Derive the shielding requirements using the empirical formula and use graphs to check that thicknesses are reasonably accurate.
You may disagree or prefer to be more conservative with the occupancy factors.
If the wall requires lead, the minimum code easily available is Code 3 but if the amount of lead is very small it is usually worth seeing if the material and thickness of the existing wall would be sufficient.
Wall B requires exactly 1.32mm Pb (Code 3). In this case it would be prudent to advise using the higher code (Code 4).
Thicknesses of concrete should normally be rounded up to the nearest 50mm.