Figure excerpt from NCRP Report No. 147, Structural Shielding Design for Medical X-Ray Imaging Facilities
Fig. 4.6b. The concrete (standard-weight) thickness requirements for primary barriers assuming preshielding (xpre) in the representative radiographic room as a function of NT/Pd2 (see Section 4.1.6.2 for caveats on xpre). P is in milligray per week, N is the weekly total number of patients examined in the radiographic room, and d (in meters) is chosen as the distance from the most intense radiation source to the occupied area. Image-receptor data as in Figure 4.5b. If the Wnorm values given in Table 4.5 do not match the per patient workload for the facility under consideration, then the original value of NT/Pd2 can be multiplied by Wsite /Wnorm, and the modified value can be used to obtain the required shielding from Figure 4.6b.