Sandra Hopkins Final Report.pdf - University of Surrey

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AbstractRoutine Coronary Angiography is a relatively high dose diagnostic procedure. The results from adiagnostic procedure may indicate the need for an interventional examination, which has thepotential for even higher patient dose. Doses for these procedures are monitored via an integrateddose area product meter (DAP). Calibrated dose area product meters were used to measure DAP fora group of standard sized patients and compared against recommended reference levels. This wascarried out on two virtually identical systems that were installed approximately 5 years apart.Results indicated that patient doses were higher on the new lab despite cardiologist techniqueappearing to have improved (25.1Gy.cm 2 for the old lab and 32.2Gy.cm 2 for the new lab). The mainreason for this increase was due to dose saving filters not being automatically inserted by the systemduring acquisition runs in the new lab. Medical Physics are working with applications specialistsand users with the aim of reducing doses in the new cath lab below the 29Gy.cm 2 reference level.The equipment also has a skin dose indicator, which can be used to monitor skin dose to warn usersif dose levels might reach the deterministic 2Gy threshold. This skin dose value assumes allradiation is directed at the same region of the skin. However, the change in x-ray tube orientationthroughout a procedure means that the dose is distributed around the patient’s back. A Matlabprogram was previously developed for a different piece of imaging equipment to replicate the dosedistribution and determine the region of maximum dose on the patient’s back. This was adapted forthe local equipment. Gafchromic film was used to produce a visual indication of how the dosewould be distributed in order to compare with the local Matlab programme. An exact match was notfound but the programme was felt to be sufficient to warn users whether skin effects were apossibility. Measurements using TLDs highlighted the fact that skin dose values are an underestimate as they do not include any contribution from scattered radiation from nearby acquisitionruns. The programme was used on a sample of routine diagnostic coronary examinations. Thisdemonstrated that there should not be any risk of skin effects for this standard procedure. Theprogramme was also used to demonstrate skin dose distribution in a more complex interventionalcase. These complex procedures need to be analysed on a case by case basis as it is difficult togeneralise on the dose distribution and the possibility of skin effects. However, it is possible for the2Gy limit to be reached during a complex interventional examination and the local programmewould be able to determine which regions of the patient’s back would be of most concern. It isexpected that doses should be lower with digital flat plate detectors but evidence demonstrates thatthis is not always the case. Optimisation work must be carried out on new equipment to ensure thatdoses are always as low as reasonably practical in line with current legislative requirements.I
AcknowledgementsI would like to express my gratitude to the following people for their assistance and advice. In thecardiac catheterisation laboratories at Portsmouth Hospitals NHS Trust: Clare Smith for her supportwith the collection of patient dose data. To all my colleagues in the Radiological Sciences Groupfor covering for me and encouraging me whilst I worked on this project. A special thank you toAntonio De Stefano for working through the programming aspects of the project. Finally, manythanks to my supervisors: Anne Davis from Portsmouth Medical Physics and Professor PatrickRegan of the University of Surrey for their support and advice.II
Page 1: Calculation, verification and monit
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 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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