RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY

1. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology RADIATION PROTECTION INDIAGNOSTIC ANDINTERVENTIONAL RADIOLOGY Part 12.1 : Shielding and X-ray room design Practical exercise

2. Overview and Objectives • Subject matter: design and shielding calculation of a diagnostic radiology department • Step by step procedure to be followed • Interpretation of results 12.1 : Shielding and X-ray room design

3. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology Part 12.1 : Shielding and X-ray room design Design and shielding calculation of a diagnostic radiology department Practical exercise

4. Radiation Shielding— Calculation • Based on NCRP 147, Structural Shielding Design for Medical X-Ray Imaging Facilities. • Assumptions used are conservative, so over-shielding is typical • Computer software is available, giving shielding in thickness of various materials 12.1 : Shielding and X-ray room design

5. Radiation Shielding– Calculation NCRP 147 Provides methods to calculate the thickness of shielding needed to decrease the kerma in a shielded area to P/T P = the weekly permitted kerma in the occupied area T = the occupancy factor, the average fraction of time that the maximally exposed individual is present while the x-ray beam is on. 12.1 : Shielding and X-ray room design 5

6. Radiation Shielding– Calculation NCRP 147 provides K1, the average kerma expected for a patient procedure 1 m from the x-ray tube in the primary beam (Table 4.5), and, 1 m from the patient from secondary (scatter and leakage) radiation (Table 4.7) Then, the unshielded weekly kerma, K0 at distance d for N patient procedures per week is 12.1 : Shielding and X-ray room design 6

7. Radiation Shielding– Calculation Then the acceptable thickness, x, of a shielding barrier will be that which provides transmission, B, not in excess of 12.1 : Shielding and X-ray room design 7

8. Radiation Shielding– Cardiac Cath Consider a wall in a cardiac cath lab, with d=4 m, P = 0.02 mGy wk-1, T=1, 90° scatter, N=25 patients wk-1 From NCRP 147, Table 4.7, for a cardiac cath lab: K1 = 2.7 mGy patient-1 Total unshielded weekly kerma is then 12.1 : Shielding and X-ray room design 8

9. Radiation Shielding– Cardiac Cath Required transmission is Look at transmission curve for secondary radiation from Cardiac Cath Lab (NCRP 147, Fig. C.2) Requires 1.2 mm Pb. 12.1 : Shielding and X-ray room design 9

10. Shielding Calculation– Cardiac Cath B=0.0047 x =1.2 mm Pb 12.1 : Shielding and X-ray room design

11. Radiation Shielding– R-F Room For general radiographic or fluoroscopic rooms, the x-ray tube(s) may generate primary beams directed at a number of barriers, as well as scatter and leakage radiations from these beams NCRP 147 § 4.5 specifies thicknesses required for primary and secondary barriers in these rooms as a function of NT/(Pd2) Note that NCRP 147 § 4.5 accounts for all primary and secondary radiation sources in the room. 12.1 : Shielding and X-ray room design 11

12. Radiation Shielding– R-F Room Consider the floor in a general radiographic room. Let N = 125 patients wk-1, d = 3.8 m, P = 0.02 mGy wk-1, T = 1. Then NT/Pd2 = 432 mGy-1 m-2 , which, from Fig. 4.6a, requires 110 mm of concrete. This ignores attenuation in the image receptor and its supports. 3.8 m Fully occupied uncontrolled area 12.1 : Shielding and X-ray room design 12

13. Shielding Calculation– R-F Room NCRP 147 Fig 4.6a NT/(Pd2) = 432 mGy-1 m-2, requiring a floor thickness of 110 mm standard density concrete 12.1 : Shielding and X-ray room design 13

14. Radiation Shielding– CT Scanner Computed tomography (CT) scanners will generate scatter and leakage radiation to the environs of the room. For every 10 mm of x-ray beam width, the intensity of this secondary radiation at 1 m is a fraction, , of the peripheral CTDI100. Head scans:  = 910-5 Body scans:  = 310-4 12.1 : Shielding and X-ray room design 14

15. Radiation Shielding– CT Scanner Since the product of the CTDI used for each patient and the thickness of the patient imaged is the Dose Length Product, DLP, the unshielded kerma at 1 m from each patient is: The DLP values can be read off of the scanner, or from European Commission Guidelines: DLP = 1,200 mGy cm for heads DLP = 550 mGy cm for bodies 12.1 : Shielding and X-ray room design 15

16. Radiation Shielding– CT Scanner Consider a barrier in a CT scanner room, with P = 0.02 mGy wk-1, T = 1, d=3 m, 200 patients wk-1 (125 bodies + 75 heads), with 40% of patients having scans both pre- and post-contrast medium injection 12.1 : Shielding and X-ray room design 16

17. Radiation Shielding– CT Scanner The unshielded kerma per head patient at 1 m is: The unshielded kerma per body patient at 1 m is: So total unshielded weekly kerma at 1 m is 12.1 : Shielding and X-ray room design 17

18. Radiation Shielding– CT Scanner The unshielded weekly kerma at 3 m is The transmission required in this barrier is which, from NCRP 147 Figs. A2 and A3, at 140 kVp, is achieved by 1.52 mm Pb, or, 150 mm standard density concrete 12.1 : Shielding and X-ray room design 18

19. Shielding Calculation– CT Scanner 12.1 : Shielding and X-ray room design 19

20. Shielding Calculation– CT Scanner 12.1 : Shielding and X-ray room design 20

21. Radiation Shielding– CT Scanner Note that, should the ceiling require added shielding, wall shielding should be extended up to the ceiling in order to cover the gap above the normal shielding height. Additional Pb required on ceiling ADD Pb to wall above 2.1 m CT Scanner 12.1 : Shielding and X-ray room design 21

22. Where to Get More Information • National Council on Radiation Protection and Measurements, Report 147, Structural Shielding Design for Medical X-Ray Imaging Facilities, NCRP, Bethesda, MD. 2004 12.1 : Shielding and X-ray room design