Sandra Hopkins Final Report.pdf - University of Surrey

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Further combined orientations were trialled in order to assess how closely the Model recreated theactual distribution.It was also possible to manipulate patient dose records to amend the tube angle in order to simulateparticular orientations in order to carry out further analysis of the image display for the Matlabprogramme.3.5 Analysis of Skin dose data using in house dose distribution softwareThe adapted programme was used to calculate the peak skin dose for a number of routine diagnosticexams in order to determine whether deterministic effects are of concern for this type of exam andwhat would be a typical maximum skin dose value based on the indicated Dose Area Product value.Additionally the programme was trialled on a therapeutic exam to ascertain how it might be used inpractise in a clinical environment to determine when a patient requires monitoring for skin effects.19
4. Results4.1.1 Verification of Dose Area Product CalibrationTable 3 shows the results of measurements carried out to determine the accuracy of the Dose AreaProduct meter in the new lab. The field area was measured to be (0.013 +/- 0.002)m 2 . This wasmeasured at the same distance as the ionisation chamber.Set kV DisplayedmA+/- 2%Measured dosemGyCalculated DoseArea ProductµGy.m 2Displayed DoseArea ProductµGy.m 2Difference betweenindicated andactual %50 762.1 18.3 +/- 0.7 342 +/- 7 336.2 -1.5%66 329.9 12.6 +/- 0.5 235 +/- 5 234.8 +0.1%81 74.5 6.5 +/- 0.3 121 +/- 2 122.6 +1.1%81 74.5 6.5 +/- 0.3 121 +/- 2 122.4 +1.0%96 39.4 3.9 +/- 0.2 74 +/- 1 78.2 +6.1%109 44.3 5.5 +/-0.2 103 +/- 2 107.1 +3.8%Table 3 : Measurements to determine the accuracy of the Dose Area product meterThus, for the entire kilovoltage range the indicated Dose Area Product was within 7% of the actualvalue. This is considered to be good accuracy. For the old lab the Dose Area Product was measuredto be within 10%4.1.2 Verification of Skin Dose Indicator CalibrationMethod 1 - Ion chamber free in airDisplayedkVDisplayedmA+/- 2%IndicatedmGy/min+/-5%MeasuredmGy/min+/- 4%Differencebetween indicatedand actual70 187 72 63.5 +13.4%60 138 35 31.4 +11.5%50 752 165 152.4 +8.3%81 166 82 73.8 +11.1%90 312 221 196.1 +12.7%90 555 450 404 +11.4%70 181 68 61.7 +10.5%20
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 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 33 and 34: 4.3.2 Simulated patient Skin Absorb
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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