Sandra Hopkins Final Report.pdf - University of Surrey

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1. IntroductionThe use of ionising radiation for clinical diagnosis is a long established method for the examinationof a variety of medical conditions. Different imaging modalities and complexities of examinationsmean that some procedures contribute more to patient dose than others. Figure 1 shows thecontribution of the collective dose from the 15 diagnostic examinations which provided the largestcontribution to the collective dose. It can be seen that, with the exception of Computed Tomography(CT), routine diagnostic coronary angiography provides the largest contribution to the collectivedose in the UK. Although the frequency of the examination is low (0.4%), the dose for eachexamination can be high. UK estimates calculate that this exam produces 5.6% of the totalcollective dose 1 . A more recent study for the European population estimates that this contributionhas increased 2 and this is attributed to the fact that this procedure can be performed on an outpatient basis and causes less trauma than surgical procedures. There have also been technicaldevelopments which have led to an increase in frequency such as the introduction of digitaldetectors and the evolution of stents. Coronary angiography is the standard technique for imagingthe left ventricle and coronary arteries. It is a routine diagnostic procedure with a clearly establishedmethod for performing it. Although patient doses are considered to be relatively high for adiagnostic procedure, using current imaging techniques it is unlikely to ever reach a level wheredeterministic effects could be considered a possibility. However, the results of a diagnosticexamination may indicate that treatment is required. This treatment could involve a more complexinterventional procedure such as a graft or insertion of a stent.Figure 1. Contribution to UK collective dose and frequency from the 15 exams making the biggest contribution to thecollective dose 1 .181614Collective DoseFrequency% contribution121086420CT abdomenBa EnemaCT chestCT pelvisCT HeadCoronary AngiographyAbdomenLumbar SpinePelvisMammographyIVUPTCAArteriographyHipCT Spine1
These types of interventional procedures can be very complex and there is the potential to achieveskin entrance doses that could potentially lead to deterministic effects such as skin damage.The FDA (Food and Drug Adminstration) publication gives advice on precautions to be taken toreduce skin dose 3 . The biological effects of ionising radiation on the skin have been analysed by theInternational Commission on Radiological Protection (ICRP) who have published advice andguidance 4,5,6 .With increased user awareness and developments in imaging techniques there have been far lessincidence of skin damage. However, it is still possible that skin damage could occur in complexcases and some imaging equipment designers have included a skin dose indicator on theirequipment. This indicator provides the total accumulated skin dose for a single examination.However, this value assumes that the x-ray beam orientation has been continually focussed in onedirection so that the same area of skin has been irradiated throughout the entire procedure. Inreality, this is rarely the case and the x-ray beam will be oriented in a variety of ways to improvevisualisation of particular coronary vessels. This will mean that the accumulated skin dose is anover estimate of the actual maximum skin entrance dose to the patient and can be misleading andthis has been acknowledged in other studies 7 . Although, the indicator is a good warning device tolet users know that the total patient skin dose is high it does not give them a true indication of thedistribution of the dose on the patient’s skin. Users would benefit from knowing when it is likelythat the skin damage threshold has been reached so that in this case the patient can be followed upand appropriate treatment and consultation be provided as required. Some manufacturers havepreviously developed computer packages to monitor skin dose distribution but these are no longercommercially available. Attempts have since been made to develop dose distribution software 8,9 .This current project includes adaptation of existing software to provide skin dose distributioninformation for local equipment.2. Theory2.1 Cardiac AngiographyThis is one of the most commonly performed imaging tests for evaluating the heart and its majorvessels. Coronary angiography can show the exact site and severity of the narrowing of arteries.After the introduction of a catheter into a peripheral vessel, usually the femoral or axilliary vein orartery, the cardiologist, under direct fluoroscopic visualisation, guides the catheter intravascularly tothe region of interest, injects contrast media to confirm the location of the catheter then injects2
Page 1 and 2: Calculation, verification and monit
Page 3 and 4: AcknowledgementsI would like to exp
Page 5: 4.3.2 Simulated Patient Skin Absorb
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
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