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R D(t) = . t D(0) × t Equation 5.8 T = 1.443× t ½ × 1− exp − 0.693t T ½ where D(t) = Total dose (μSv) over a time t at 1 m from the patient Ḋ(0) = Dose rate (μSv/h) at 1 m at the time of administration, given by the product of the dose rate constant for the patient (0.092 μSvm 2 /MBqh for 18 F) and the administered activity A 0 (MBq) t = Time (min) of interest T ½ = Half life (min) of the radionuclide For 18 F, this corresponds to R t factors of 0.91, 0.83, and 0.76 for t = 30, 60, and 90 min, respectively. Decay before Imaging Because of the decay since the administration of the radionuclide (uptake phase), the activity in the patient at the commencement of imaging is decreased by F = exp u -0.693t T ½ u Equation 5.9 where t u is the uptake time (min) and T ½ is the half life (min) Physiological decay In most cases the patient will void prior to imaging, removing approximately 15% of the administered activity and thereby decreasing the dose rate by 0.85. Calculation of exposure at a boundary Equation 5.7 may be used for the calculation of total exposure at a boundary, a distance d metres, from the patient. Uptake room The total dose (μSv), at a distance d (m), from a patient during the uptake time, t u (min), will be given by R D(t u ) = D(0) . × tu × d tu 2 Equation 5.10 64 The Design of Diagnostic Medical Facilities where Ionising Radiation is used
where Ḋ (0) is the product of the dose rate constant for the patient (0.092 μSvm 2 /MBqh for 18 F) and the administered activity A 0 (MBq) and R tU is the reduction factor for the uptake time. Imaging room To calculate the dose from a patient during imaging, the decay during the uptake phase must be taken into account. In addition the reduction factor of 0.85 as a result of patient voiding should also be taken into account. The total dose (μSv) at a distance d (m) from the patient is given by F D(t i ) = D(0) . × ti × Rti × 0.85 × d u 2 Equation 5.11 where Ḋ (0) is the product of the dose rate constant for the patient (0.092 μSv m 2 /MBqh) for 18 F and the administered activity A 0 (MBq), R ti is the reduction factor for the imaging time t i and F u is the decay in the radionuclide activity since administration. To calculate the annual dose at a boundary, the calculated dose should be multiplied by the annual workload. The maximum allowable transmission can then be calculated using the dose constraint and occupancy factors in a similar manner to that employed in X‐ray. Shielding factors A variety of attenuation coefficients has been used to estimate transmission requirements for PET facilities. In some cases narrow-beam, good geometry attenuation coefficients for lead and concrete have been used. However, calculations based on these values will not provide sufficient shielding since they neglect scatter buildup factors. The AAPM recommends using values of broad beam transmission factors for lead, concrete, and iron that are based on consistent Monte Carlo calculations. Plots of the broad beam transmission at 511 keV are given in Appendix D for lead and concrete. The transmission factors for 18 F through lead and concrete are also given. 5.3 Examples of shielding calculations Examples of shielding calculations for radiology, nuclear medicine and PET facilities are presented in Sections 5.3.1 and 5.3.2. The aim of the radiology examples is to show how the BIR and NCRP methodologies may be applied in particular cases using the dose constraints in Table 2.1 and other local data. In practice it may be prudent in marginal cases to calculate the shielding requirements using both methodologies. The examples are provided for illustrative purposes only and are not intended to substitute for the RPA’s assessment. The Design of Diagnostic Medical Facilities where Ionising Radiation is used 65
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RPII 09/01 The Design of Diagnostic
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Foreword The original Code of Pract
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4. Nuclear medicine 35 4.1 Introduc
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1. Legal and administrative framewo
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e made as soon as possible. It shou
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It should be noted that it is the u
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Records should be kept as they will
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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
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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
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Page 48 and 49: The layout of the department should
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Page 52 and 53: 5. Shielding calculations 5.1 Gener
Page 54 and 55: Table 5.2: Suggested minimum distan
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
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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
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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
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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
Page 104 and 105: Figure E.7: Shielding around the ed
Page 106 and 107: Figure F. 3: Sample radiation warni
Page 108 and 109: Notes 106 The Design of Diagnostic
Page 110: Notes 108 The Design of Diagnostic
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