iaea human health series publications - SEDIM

8.8. DOSIMETRY8.8.1. Mean glandular dose (D G )8.8.1.1. Scope— Objective: To estimate the MGD (D G ) for breasts represented by PMMA thicknesses of 20, 45 and 70 mm[8, 48, 60, 64, 65].— Minimum frequency: Annually and after equipment changes.8.8.1.2. Methodology(1) The MDG (D G ) is obtained from the incident kerma in air and relevant conversion coefficients using thefollowing formula 26 :D G = g t c t s K i,t (9)whereK i,tg tc tsis the entrance air kerma at the surface of the slab of PMMA (20, 45 and 75 mm thick), used to simulatethe standard breast with a thickness of t mm, measured without backscatter (see Section 8.7.2);is the factor that converts from air kerma to MGD for a breast having a 50% fibroglandular/50% fatcomposition with a thickness of t mm;is the conversion factor which allows for the glandularity of a standard breast of thickness t mm;is the s factor, which gives a correction that depends on the target–filter combination.(2) Use the product of the g and c factors, which are dependent on the HVL of the spectra utilized, as provided inTable 16.(3) The HVL value is obtained following the method described in Section 8.7.1.(4) Apply the values of the s factor for the relevant target–filter combination provided in Tables 19 and 20.(5) Record the values of g, c, s, HVL and D G on Chart 11 in Annex II.8.8.1.3. Interpretation of results and conclusionsTable 21 provides acceptable and achievable limits for the MGD (D G ).8.8.1.4. Recommendations and corrective actions(1) Observe the variation of D G over time; if the limits are exceeded, investigate the possible causes and take thenecessary corrective measures.(2) It is recommended that the MGD also be estimated from actual patient exposures periodically, and that thevalues be compared with the diagnostic reference levels that have been established at the local or nationallevel [48, 64–66, 68].26Note that this definition uses the formula used in Europe and the United Kingdom, which uses an expected average glandularcontent as shown in Table 16 instead of that given previously [66], where the glandularity was assumed to be 50%.113