Sandra Hopkins Final Report.pdf - University of Surrey

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Skin injuries can occur when skin dose levels exceed the 2Gy threshold for deterministic effects.With protracted examinations there is a risk to the patient of a deterministic effect occurring. Asummary of the potential effects from cardiac exposures on the reaction of the skin is given in table1. Skin effects have been discussed in the literature and retrospective assessments of skin dosemade 14, 15, 16, 17, 18, 19 .2.4.3 Dose reference LevelsA joint document by the Royal College of Radiologists (RCR) and the National RadiologicalProtection Board (NRPB) produced a document in 1990 suggesting the concept of a reference dosein order to indicate ‘abnormally high doses’ 20 . In 1992 a National Protocol was developedsuggesting methods on how local departments could compare their doses with these NationalReference Doses 21 . The suggestion was to take a representative sample of close to standard sizedpatients and compare the mean with the reference dose. The reference dose was the third quartilevalue derived from a national database of dose data from many contributing hospitals. If the meandose exceeded this reference dose then an investigation was required in order to take correctiveaction or to justify the high dose on clinical grounds. This same concept was adopted by theInternational Commission on Radiological Protection (ICRP) 5, 22 and the Diagnostic ReferenceLevel was introduced. In 1997 this concept was taken up as a European Medical ExposureDirective 23 and the requirements of this were implemented in the UK by the Ionising Radiation(Medical Exposure) Regulations 2000 24 . In IRMER, Diagnostic Reference levels (DRL) weredefined as ‘dose levels for typical examinations for groups of standard-sized patients or standardphantoms and for broadly defined types of equipment’. It is important to note that this relates to‘diagnostic examinations’ so will apply to routine diagnostic coronary angiography examinationsbut does not apply to therapeutic coronary exams such as angioplasties. DRLs are based on anational database which is extended and revised every five years. Recommended DRLs for thecurrent database are determined from this data 25, 26 . For Coronary Angiograms the current andpreviously recommended DRL is given in the table 2.9
NRPB W-14 25(June 02)HPA-RPD-029 26(August 07)Recommended DRL DAP per exam (Gy.cm 2 ) 36 29Number of hospitals 7 38Fluoroscopy time per examination (seconds) 294 243Mean patient range 75 – 85 kg 75 – 85 kgNumber of rooms 17 110Number of patients 8000 34236Fluoroscopy time range (seconds) 185 to 385 93 to 606Third quartile time (seconds) 337 270Mean DAP (Gy.cm 2 ) 30.4 25.7DAP range (Gy.cm 2 ) 11.8 to 60.7 11.7 to 72.5First quartile DAP (Gy.cm 2 ) 22.3 18.9Third quartile DAP (Gy.cm 2 ) 36.3 29.0Patient age (years) 60(16-97) 62 (16-99)Patient weight (kg) 78(35-172) 79(29-183)Number of images per exam Not available 737(6-2200)Table 2 : Summary of data used to derive Diagnostic Reference Levels2.4.4 Guidance for high skin dose proceduresAlthough guidance documents 25, 26 do give some data on Coronary angioplasties, strictly speakingDiagnostic Reference Levels do not apply. However there have been studies of doses frominterventional cardiac examinations where reference levels have been proposed 27, 28 . Moreemphasis is placed, however, on making interventionists more aware of the potential injury fromthese procedures and methods for decreasing their incidence by using dose control strategies 6 .2.5 Measuring Patient Dose - Dose Area Product Meter and Skin dose indicatorThe dose area product (DAP) meter is a measure of dose in Gray multiplied by the area irradiated.This gives an indication of patient dose that can be used to compare with the same parameter for thesame exam. DAP is an easily available measurement which is commonly used to monitor patientdoses for many routine diagnostic imaging procedures. Some imaging systems calculate the DAPfrom known exposure factors but it is understood that the Siemens Axiom Artis uses an integralionisation chamber to determine the DAP. In addition to this value, the system also gives a value ofskin entrance dose in mGy. This is calculated at a reference point of 60cm from the focal spot. Thisis equivalent to a distance of 15cm in front of the isocentre which is taken to be the most typical10
Page 1 and 2: Calculation, verification and monit
Page 3 and 4: AcknowledgementsI would like to exp
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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
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Page 33 and 34: 4.3.2 Simulated patient Skin Absorb
Page 35 and 36: However, a second set of orientatio
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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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