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1、RADIATION PROTECTION INDIAGNOSTIC ANDINTERVENTIONAL RADIOLOGY,Part 12.1:Shielding and X-ray room designPractical exercise,IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology,12.1:Shielding and X-ray room design,2,Overview and Objectives,Subject matter:design and
2、 shielding calculation of a diagnostic radiology department Step by step procedure to be followedInterpretation of results,Part 12.1:Shielding and X-ray room design,Design and shielding calculation of a diagnostic radiology departmentPractical exercise,IAEA Training Material on Radiation Protection
3、in Diagnostic and Interventional Radiology,12.1:Shielding and X-ray room design,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 typicalComputer software is available,giving shi
4、elding in thickness of various materials,12.1:Shielding and X-ray room design,5,Radiation Shielding Calculation,NCRP 147Provides methods to calculate the thickness of shielding needed to decrease the kerma in a shielded area to P/TP=the weekly permitted kerma in the occupied areaT=the occupancy fact
5、or,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,6,Radiation Shielding Calculation,NCRP 147 provides K1,the average kerma expected for a patient procedure1 m from the x-ray tube in the primary beam(Table
6、 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,7,Radiation Shielding Calculation,Then the acceptable thickness,x,of a shielding barrier w
7、ill be that which provides transmission,B,not in excess of,12.1:Shielding and X-ray room design,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-1From NCRP 147,Table 4.7,for a cardiac cath lab:K1=2.7 mGy patient-1Tota
8、l unshielded weekly kerma is then,12.1:Shielding and X-ray room design,9,Radiation Shielding Cardiac Cath,Required transmission isLook 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,10,Shielding Calculatio
9、n 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 beamsNCRP 147 4.5
10、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,12,Radiation Shielding R-F Room,Consider the floor in a general
11、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.,Fully occupied uncontrolled area,3.8 m,12.1:Shielding and X-ray room design,13,Shielding Ca
12、lculation 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,14,Radiation Shielding CT Scanner,Computed tomography(CT)scanners will generate scatter and leakage radiation to the environs of the room.F
13、or 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:=910-5Body scans:=310-4,12.1:Shielding and X-ray room design,15,Radiation Shielding CT Scanner,Since the product of the CTDI used for each patient and the thickness
14、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 headsDLP=550 mGy cm for bodies,12.1:Shielding and X-ray room design,16,Radiation Shielding C
15、T 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,17,Radiation Shielding CT Scanner,The unshielded kerma per head pa
16、tient 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,18,Radiation Shielding CT Scanner,The unshielded weekly kerma at 3 m isThe transmission required in this barrier iswhich,from NCRP 147 Figs.A2 and A3,at 140
17、 kVp,is achieved by 1.52 mm Pb,or,150 mm standard density concrete,12.1:Shielding and X-ray room design,19,Shielding Calculation CT Scanner,12.1:Shielding and X-ray room design,20,Shielding Calculation CT Scanner,12.1:Shielding and X-ray room design,21,Radiation Shielding CT Scanner,Note that,should
18、 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.,CT Scanner,Additional Pb required on ceiling,ADD Pb to wall above 2.1 m,12.1:Shielding and X-ray room design,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,
