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Table 5.2: Suggested minimum distances to the vital organs of an occupant in an adjoining area Boundary Walls Ceilings Floors Minimum distance to occupant in adjoining area 0.3 m 0.5 m from floor above 1.7 m from floor below Based on NCRP, 2004. Figure 5.1: Suggested minimum distances to the vital organs of an occupant in adjoining area 0.5m Room above X-ray tube (source of primary radiation) Patient (source of scattered radiation) 0.3m Patient table Room below 1.7m Adapted from NCRP, 2004 5.2.2 Workload in radiology An essential factor in a shielding calculation is realistic knowledge of the workload for the X‐ray room in question. The BIR recommend that the workload should be based on Entrance Surface Doses (ESD) and Dose-Area Product (DAP) values (BIR, 2000). Most modern X‐ray systems are now fitted with DAP meters, making it relatively easy to obtain DAP values for the clinical workload in a particular X‐ray room. For new examinations, or where no local workload data is available, published values should be consulted for guidance. However, much of the published guidance is from UK studies and caution should be exercised as it may not always be representative of doses in Irish hospitals. In addition, published values will not necessarily reflect the current or new technology being installed. Local values should be used where possible. The workload in many rooms is increasing for reasons that include increased working hours, faster patient throughput with some digital imaging systems, and the increases in the number and complexity of procedures. The most satisfactory workload data used for shielding design is based on a realistic audit of current practice, projected for any envisaged increases in the future. It is better to generously provide for this at the beginning of the project, as retrofitting additional shielding at a later stage will be expensive. Consideration should also 52 The Design of Diagnostic Medical Facilities where Ionising Radiation is used
e given to exposures made during quality assurance (QA) testing as this may add significantly to the workload (BIR, 2000). Many studies which are helpful in determining workload are available, and a few are cited here. For example, ESD values are available from NRPB reports and the European Guidelines on Quality Criteria for Diagnostic Radiographic Images. Ranges of dental DAP and ESD values have been published and doses from CT examinations are also available (EC, 1996b, BIR, 2000, NRPB, 2002, NRPB, 2005). Little data is available from Irish hospitals although limited ESD values for some common projections have been published (Johnson & Brennan, 2000). DAP values for some common examinations from UK data are reproduced below in Table 5.3 (NRPB, 2002). The DAP values published in BIR (2000) have now been superseded by these. Table 5.3: DAP values for common X‐ray examinations (based on NRPB 2002) Examination DAP (Gy cm 2 ) Mean Max. Lumbar Spine AP 1.4 3.7 Lumbar Spine Lat 2.3 5.8 Lumbar Spine LSJ 2.4 6.7 Chest PA 0.10 0.24 Abdomen AP 2.5 8.2 Pelvis AP 2.2 7.3 An alternative approach to workload determination is used by the NCRP and is based on tube current and “beam-on” time. It is the amount of time that the X‐ray beam is producing radiation multiplied by the current, in units of milliampere minutes (mA.min), or mA.min per week (NCRP, 2004). A patient may have multiple exposures during an examination and the average workload per patient is given by W norm . The total weekly workload, W tot , is calculated by multiplying W norm by the average number of patients per week (N). W norm values were determined (for several types of X‐ray installation) from a survey of American institutions and are reproduced in Table 5.4. For a general radiography room, the workload in the case of “all barriers”, “chest bucky” only and “floor or other barriers” is presented as is the workload for a room containing both a general radiographic tube and a fluoroscopy tube (R&F room) (NCRP, 2004). The Design of Diagnostic Medical Facilities where Ionising Radiation is used 53
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RPII 09/01 The Design of Diagnostic
Page 4 and 5: Foreword The original Code of Pract
Page 6 and 7: 4. Nuclear medicine 35 4.1 Introduc
Page 8 and 9: 1. Legal and administrative framewo
Page 10 and 11: e made as soon as possible. It shou
Page 12 and 13: It should be noted that it is the u
Page 14 and 15: Records should be kept as they will
Page 16 and 17: 2. Identify the persons (staff and
Page 18 and 19: 3.1.3 Computed Tomography (CT) CT a
Page 20 and 21: Photo 3.2: Interventional X‐ray r
Page 22 and 23: 3.3 Radiography rooms 3.3.1 General
Page 24 and 25: X Figure 3.2: Dedicated chest room
Page 26 and 27: Figure 3.4: DXA room Operator’s c
Page 28 and 29: Figure 3.5b: A dental radiography s
Page 30 and 31: Radiation shielding calculations fo
Page 32 and 33: There are large variations in the s
Page 34 and 35: e assessed by the RPA as part of th
Page 36 and 37: The trailer must be sited in an are
Page 38 and 39: It is recognised worldwide that the
Page 40 and 41: The operator console should be loca
Page 42 and 43: Figure 4.3: A possible layout for a
Page 44 and 45: The workstation should be adequatel
Page 46 and 47: uptake probe and associated equipme
Page 48 and 49: The layout of the department should
Page 50 and 51: The control/console room should pro
Page 52 and 53: 5. Shielding calculations 5.1 Gener
Page 56 and 57: Table 5.4: Workload data from NCRP
Page 58 and 59: 5.2.4 Primary radiation A barrier i
Page 60 and 61: The primary beam will be attenuated
Page 62 and 63: 1 χ = ln αγ B −γ 1+ + β α
Page 64 and 65: . The reduction in the dose rate fr
Page 66 and 67: R D(t) = . t D(0) × t Equation 5.8
Page 68 and 69: 5.3.1 Radiology shielding calculati
Page 70 and 71: Example 2: Dedicated chest room (BI
Page 72 and 73: Example 4: Dental X‐ray room (BIR
Page 74 and 75: Example 6: Shielding required for a
Page 76 and 77: 6. Some practical considerations 6.
Page 78 and 79: 6.1.4 Brick There are many types of
Page 80 and 81: Walls are generally shielded to ful
Page 82 and 83: 6.3.3 Doors As illustrated in Chapt
Page 84 and 85: Photo 6.4 Lead blinds protecting wi
Page 86 and 87: Chapter 2). It is becoming common t
Page 88 and 89: Gaps in shielding are more likely t
Page 90 and 91: ICRP. 2007. Recommendations of the
Page 92 and 93: Appendices Appendix A: Dose limits
Page 94 and 95: Appendix C: Radiation transmission
Page 96 and 97: Figure C.1: Transmission of primary
Page 98 and 99: Figure C.5: 2 mm lead equivalent th
Page 100 and 101: Table D.3: Physical properties & ef
Page 102 and 103: Appendix E: Schematic diagrams of r
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Figure E.7: Shielding around the ed
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Figure F. 3: Sample radiation warni
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Notes 106 The Design of Diagnostic
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Notes 108 The Design of Diagnostic
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