3Radiation Horrors No Color, no Smell Deterministic effects Threshold doseRedness of skinStochastic effectsYounger affect mostExposure to 1 Sievert of radiation is estimated to increase the lifetime risk of fatal cancer by around 5% (Atomic Bomb Study)007
4Radiation Horrors No Color, no Smell Deterministic effects Threshold doseRedness of skinStochastic effectsYounger affect mostExposure to 1 Sievert of radiation is estimated to increase the lifetime risk of fatal cancer by around 5% (Atomic Bomb Study)CT perfusion Prolonged fluoroscopy sensitivity is proportional to dividing cells 50mSv starting
5Radiation Horrors No Color, no Smell Deterministic effects Threshold doseRedness of skinStochastic effectsYounger affect mostExposure to 1 Sievert of radiation is estimated to increase the lifetime risk of fatal cancer by around 5% (Atomic Bomb Study)
62 months Background Radiation in Hong Kong Public AwarenessCXR (0.1mSv)2 months Background Radiation in Hong Kong
8Educational Pamphlet Accuracy of dose information ? Royal observatoryWhat is the examination dose level of your institute ?
9Dose Measurement Quantity Unit Determination Exposure Absorbed Dose Coulombs (C) /KgMeasure the amount of ionization produced in airAbsorbed DoseGray (Gy) or J/KgMeasure the radiation energy absorbed by the patientEquivalent DoseSievert (Sv)Multiply Absorbed Dose by a quality factor (QF) to show harmful effects, e.g.X-ray & Gamma: QF=1; Alpha particle: QF=20Effective DoseSvMultiply Equivalent Dose by a tissue weighting (TW) factor, i.e. Colon: TW=0.12; Skin: TW=0.01; Whole Body: TW=1 (ICRP 2007)Example: 100mSv to skin = Effective dose of 1mSvRecap memory different radiation has different detrimental effects
10Device for measurement Film badge TLDDAP and printerDAP is mandatory perspexVarious detectors and PhantomsTLD-100 chips (Harshaw)
11Dose Area Product Meter Reading includes SID variationReading includes Collimation factorsDAP do not measure backscatterDAP do not measure wedge or added filtersmGy/cm2
12Monte Carlo simulations The assessment of conversion factors began more than 30 years agoUse tissue-equivalent plastic body phantoms containing organs into which dosimeters are inserted and Monte Carlo simulations are appliedCommon available standard includes an adult with a body mass of 70 kg; children aged 15, 10, 5, 1 year and newbornsEffective dose: can’t measure routinelyEntrance Skin Dose is commonly usedToo hard to be accurate, too many factors
13Effective Dose Calculation The geometry of patient exposure is less predictable and varies during the procedureThe fundamental radiation dose parameter in CT is the CT dose index (CTDI & CTDIvol). To assess patient dose exposure after scanning a certain distance use dose-length product (CTDIvol × scan length)X-rayFluoroCTVerdun F R et al. Radiographics 2008;28:
14Use ESD & DAP to calculate the Effective Dose HartD, Jones DG, Wall BF. Estimation of effective dose in diagnostic radiology from entrance dose and dose-area product measurement (NRPB-R262). Chilton, England: NRPB, 1994.
15Dose Reference Levels (DRL) Introduced by ICRPDose level for typical exams for group of standard-sized patientsDRL are typically set atthe 3rd quartile of dosedistribution from asurvey
16DRL for monitoring ESD = (DAP*BSF/FieldSize)*(SID/FSD)^2 Calculation of Entrance Skin Dose (ESD) for Supine and Erect Abdomen in Digital Radiography for HA hospitalsESD = (DAP*BSF/FieldSize)*(SID/FSD)^2FSD, focus-to-skin distance = SID - 25 cmBSF, backscatter factor estimated fromNRPB SR262 (e.g. 80kVp = 1.458)
17Information from DICOM Header kVp = 110Protocol = ChestSID = 1800mmFSD = 1750mmFOV (collimation) =35.1cm x 37.1cmmAs = 3.376DAP = mGy/cm2Position = PAMapping to PACS database is required
19Usage of DRLComplied by ACR for Appropriateness Criteria
20CR vs DR CR: no kVp and mAs data Vendors have their own calculation of Exposure Index (EI) which give feedback about detector dose levelAAPM try to standardize the EIComplicated by collimation detection and post processing
26Reports and AlertsLA Law: 5 Gy collective dose over 18 months or 4 Gy single examination !!!
27IAEA Smart Card Project 2009 Tracking life time dose record for patienteHR for recording or Radiation PassportAccess anywhere by digital signatureData for monitoring public radiation levelRefine existing standard on dosimetryEnhancement in DICOM & IHE-REM for dose report and dose information communication