Sandra Hopkins Final Report.pdf - University of Surrey

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The most commonly used field size for fluoroscopy during routine coronary angiography is thenormal (25cm) field. From Table 9 it can be seen that a larger field size factor is required for thenew lab. Since the nominal specification doses are similar this will mean that the detector dose forthe new lab will be higher. Table 10 gives the values of the detector dose determined at the defaultpulse rate of 7.5 pulses per second.25cm field kV mA Added Measured Specification % differenceCopper nGy/pulse nGy/pulseOld Lab 61.5 146.9 0.6 mm 18.8 +/- 0.8 17.3 + 8.7 %New Lab 65 107.6 0.6 mm 27.6 +/- 1.1 24.1 + 14.5%20cm fieldOld Lab 63.1 155.2 0.6mm 28.2+/- 1.1 27.2 + 3.7%New Lab 65 141.3 0.6mm 34.5 +/- 1.4 31.9 + 8.2%Table 10 : Detector dose rates for fluoroscopyMeasurements are also made on acquisition. Typically the Mag 1 (20cm) field size is used whendigital acquisition is being used. Table 11 gives the measured values for both the 25cm and 20cmfield. Typically the pulse rate used for aquiring images during coronary angiography is 15 pulsesper second. The measurements below were made using this pulse rate and a default specificationdose of 0.17 µGy/pulse.25cm field kV mA Added Measured Specification % difference+/- 2% Copper µGy/pulse µGy/pulseOld Lab 64.5 383 0.3 mm 0.09 0.098 - 8.2%New Lab 81 70 0 0.14 0.16 - 12.5%20cm fieldOld Lab 64.5 485 0.3 mm 0.145 0.146 - 0.7%New Lab 81 94 0 0.20 0.19 +5.3%Table 11 : Detector dose rates for aquisitionThere are obvious differences which will be discussed in more detail later. For fluoroscopy thedetector dose for the new lab is higher than for the old lab due to the fact that the field size factor ishigher. Apart from this the exposure factors are fairly similar. For the acquisition dose, the new labdoses are higher than the old lab. Additionally, there are some significant differences in exposurefactors. These differences will have an effect on patient dose and will again be discussed later.27
4.3.2 Simulated patient Skin Absorbed Dose Rates (SADRs)Table 12 and 13 gives the measured SADRs for each lab for fluoroscopy and acquisition. Thedifferences in exposure factors between the two labs are again particularly noticeable onacquisition.25cm field kV mA+/-2%AddedCopperMeasuredmGy/minOld Lab 64.7 145 0.6 mm 4.1 +/- 0.2New Lab 68.4 102 0.3mm 4.0 +/- 0.220cm fieldOld Lab 66 164 0.6 mm 5.9 +/- 0.2New Lab 68.4 102 0.3 mm 5.3 +/- 0.2Table 12 : Patient SADRs for 19cm Perspex for fluoroscopy (7.5 pps)25cm field kV mA+/-2%AddedCopperMeasureduGy/exposureMeasuredmGy/minOld Lab 64.5 561 0.3 mm 34 +/- 1 31 +/- 1New Lab 81 171 0 78 +/- 2 70 +/- 220cm fieldOld Lab 66 615 0.2mm 59 +/- 1 52 +/- 1New Lab 81 225 0 98 +/- 3 88 +/- 2Table 13 : Patient SADRs for 19cm Perspex for aquisition (15 pps)SADRs for fluoroscopy in each lab are broadly similar with the new lab having slightly lower dosesthan the old lab. However, for acquisition doses the SADRs in the new lab are noticeably higher.The reasons for this will be discussed later.4.4 Practical verification and adaptation of skin dose distribution softwareMeasured field sizes are given in table 14:Field size X (cm) Y (cm)25cm 17 +/- 0.5 17 +/- 0.520cm (Mag 1) 13.5 +/- 0.5 13.5 +/- 0.516cm (Mag 2) 11 +/- 0.5 11 +/- 0.5Table 14 : Image field size at detector.28
Page 1 and 2: Calculation, verification and monit
Page 3 and 4: AcknowledgementsI would like to exp
Page 5 and 6: 4.3.2 Simulated Patient Skin Absorb
Page 7: These types of interventional proce
Page 12 and 13: 2.3.3 Equipment configurationFigure
Page 14 and 15: Skin injuries can occur when skin d
Page 16 and 17: couch height position when the cent
Page 18 and 19: This formula provides the idealised
Page 20 and 21: 3. Method3.1 Verification of Patien
Page 22 and 23: The field size was set to Mag 1 (20
Page 24 and 25: Further combined orientations were
Page 26 and 27: 70 183 67 60.7 +10.3%102 205 175 15
Page 28 and 29: Method 3 - Thermo Luminescent Dosim
Page 30: 13172125293337414549535761656973778
Page 35 and 36: However, a second set of orientatio
Page 37 and 38: further analysis work. An excerpt o
Page 39 and 40: Figure 29 : Intervention coronary e
Page 41 and 42: maximum skin dose to average dose 3
Page 43 and 44: of 29% 42 . Image quality assessmen
Page 45 and 46: always resulted in a reduction in d
Page 47 and 48: References1. NRPB W4 - Radiation ex
Page 49 and 50: 30. Theodorakou C and Horrocks J A,

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