3JustificationNo practice involving exposures to radiation should be adopted unless it produces sufficient benefit to the exposed individuals or to society to offset the radiation detriment it causes.Justification of exposures is primarily the responsibility of the medical professional i.e. the Radiologist.The expected clinical benefit associated with each type of procedure should have been demonstrated to be sufficient to offset the radiation detriment.
4Benefit of the radiation exposure must outweigh the risk of exposure JustificationBenefit of the radiation exposure must outweigh the risk of exposurevs
5Optimisation ALARP All exposures and radiation doses must be kept AsLowReasonablyPracticableWith economic and social factors taken into accountALARP
6OPTIMISATIONFor every exposure, operators must ensure that doses arising from the exposure are kept as low as reasonably practicable and consistent with the intended diagnostic purpose.THIS IS OPTIMISATION
7OPTIMISATION You are defined as an IRMER Operator Your ‘optimisation’ is ensuring you leave the X-ray unit/LINAC in a safe condition fit for clinical useHandover procedure
9Dose Investigation Level Once you start work with ionising radiation, you are subject to legal dose limits – 6 mSv per year for non-classified workersHowever, we have to define a Dose Investigation Level1.2 mSv per yearOr 0.1 mSv per monthThis is a level of dose that should trigger an investigation in conjunction with your RPA, and ensures that you do not receive anywhere close to the legal limit.
10LimitationIn the UK, legislation stipulates annual limits for the amount of radiation that may be received by staff and members of the publicLimits are set such that deterministic effects never happenLimits are set such that chances of stochastic effects are minimised
11Legal Dose Limits - Patients For examinations directly associated with illness – there are no dose limits
12Legal Dose Limits – Radiation Workers Radiation workers are those exposed to radiation as part of their occupationNo benefit – only riskTwo subgroups depending on level of exposure:Classified radiation workerNon-classified radiation worker
13Legal Dose Limits – Classified Workers Receive high levels of radiation exposureVery unlikely for dentalRequire annual health checkCompulsory dose monitoringFor classified workerWhole body 20 mSv per year effective dose (18 years old and above)Lens of eye 150 mSv per year equivalent doseSkin 500 mSv per year equivalent doseExtremities (hands and feet etc) 500 mSv per year equivalent dose
14Legal Dose limits for non-classified workers (all radiation workers in this Trust) Very unlikely you will need to be classifiedYou only need to be classified if you are considered to approach 3/10ths of any dose limitRelevant dose limit for you is 6 mSv whole body effective doseVery unlikely to exceed this per yearWe use a dose constraint of 0.1 mSv per month for RT and X-ray engineersRisk assessment usually show it is very unlikely this will be exceededWe monitor routinely with dose badges
15Legal Dose Limitation - Public The annual dose limit for a member of the public (e.g. office worker in room next door to x-ray)1 mSv/yrBut we use a dose constraint of 0.3mSv/yr
16Radiation Dose Absorbed Dose (Jkg-1) Amount of energy deposited per kilogramDose to an organ or tissueUnit is the Gray (Gy)DOSE TO A CERTAIN PLACE IN THE BODYEffective Dose (Jkg-1)This is the average dose to whole bodyUnit is the Sievert (Sv)This gives us the risk of contracting cancer of the x ray exposureTHIS IS THE OVERALL DOSE TO THE WHOLE BODYRADIATIONTISSUE
17Tissue Weighting Factors Breast0.12Red Bone MarrowColonLungStomachGonads0.08Bladder0.04LiverOesophagusThyroidSkin0.01Bone surfaceBrainKidneysSalivary glandsRemainder
18Risks Associated with X rays Adult Exposure (per 1 mSv)Fatal cancer (all types) 1 in 20,000Fatal leukaemia 1 in 200,000Non fatal cancer 1 in 100,000Heritable effects 1 in 80,000Childhood exposureFatal cancer 1 in 10,000Foetal exposureFatal cancer to 15 years 1 in 10,000All cancers to 15 years 1 in 17,000Heritable effects 1 in 42,000
19Small Risks, So why worry?... Average effective dose for radiography ~0.5 mSvRisk of fatal cancer only 1 in 40,000But, large number of patientsprocedures.Therefore, 700 patients ‘killed’ each year due to x-rays.So:All exposures must be JUSTIFIED.Doses to patients, and staff, must be As Low As Reasonably Achievable (ALARA principle).
22Doses in PerspectiveEffective dose from natural background radiation in the UK is approximately 2.7 mSvThis is 2000 times greater than a dental exposureThis natural radiation comes fromcosmic rays,rocks and soil,food,radon.Artificial radiation comes from:Fallout from nuclear explosionsRadioactive waste discharged from nuclear power plantsMedical and dental exposuresOccupational exposures
23Practical methods to restrict YOUR radiation exposure TimeDistanceShielding
27DistanceOperator B receives only a quarter of the radiation received by Operator A if he is standing twice the distance from the sourceOperator B receives only one ninth of the radiation received by Operator A is he is standing 3 times the distance from the source
31Dose monitoring Film badges Thermoluminescent dosemeters (TLD) ExtremitiesIonisation chambers
32Film badges Plastic frame Worn outside of clothes for 1 to 3 months Advantages:Provide a permanent record of doseMeasure type and energy of radiationSimple and robustDisadvantagesNo immediate indication of exposureProcessing can lead to errorsProne to filter loss
33TLD Similar use as for film badges They absorb radiation and release this as light when heatedAdvantages:Re-usableEasy to read outDisadvantages:Read out is destructiveLimited info on type of radiation
34Ionization chambers Used by scientific personnel to measure beam dose Radiation ionises air inside chamber which produces a current of electricityAdvantagesVery accurateImmediate read outDisadvantagesNo permanent recordNo indication of type of radiationFragile and easliy damaged
35Patient Doses in Radiography - Patient Dose Limitation & Practical Principles of Radiation Protection
36What are patient doses? Absorbed dose in mGy Effective dose in mSv Dose to a certain place in the body (eg skin dose)Effective dose in mSvTakes into account the tissues that have been exposed
37How do we measure these in practice? Dose Area Product meters (DAP)Skin dose:kV, mAs, focus to skin distanceScreening timeDose Length Product (CT Scanning)
38Dose Area Product Stochastic risks approx. proportional to DAP Skin dose is DAP / area irradiated1 Gy.cm2 3 mGy skin dose1 Gy.cm2 0.2 mSv effective dose .
39Largest Exposure from man-made radiation is Medical 46 million medical & dental x-rays in UK annuallyMajor Contributors to UK collective dose from medical x-rays2008 data – HPA-CRCE-012 published Dec 2010
40RADIATION EXPOSURE OF THE UK POPULATION FROM MEDICAL AND DENTAL X-RAY EXAMINATIONS From NRPB/HPA data2008 data – HPA-CRCE-012 published Dec 2010
41RADIATION EXPOSURE OF THE UK POPULATION FROM MEDICAL AND DENTAL X-RAY EXAMINATIONS From NRPB/HPA data
43Hundreds of cancer cases blamed on dentist x-rays Independent.co.uk By Jeremy Laurence, Health Editor Friday, 30 January 2004Radiation from X-rays in dentist surgeries and hospitals causes 700 people in Britain to develop cancer each year, researchers say today.
44700 CANCER CASES CAUSED BY X-RAYS 30 January 2004700 CANCER CASES CAUSED BY X-RAYSX-RAYS used in everyday detection of diseases and broken bones are responsible for about 700 cases of cancer a year, according to the most detailed study to date.The research showed that 0.6 per cent of the 124,000 patients found to have cancer each year can attribute the disease to X-ray exposure. Diagnostic X-rays, which are used in conventional radiography and imaging techniques such as CT scans, are the largest man-made source of radiation exposure to the general population. Although such X-rays provide great benefits, it is generally accepted that their use is associated with very small increases in cancer risk.
45Researchers from Oxford University and Cancer Research UK estimated the size of the risk based on the number of X-rays carried out in Britain and in 14 other countries.According to their findings, published in the medical journal The Lancet, the results showed that X-rays accounted for 6 out of every 1,000 cases of cancer up to the age of 75, equivalent to 700 out of the 124,000 cases of cancer diagnosed each year.
46Un-necessary exposures Those exposures that are:unlikely to be helpful to patient management, orare not As Low As is Reasonably Practicable in order to meet a clinical objective.
47Practical Optimisation for Patient Protection - ALARA
48Factors affecting Patient Dose Field Size (Collimation)Tube voltage (kV)Beam filtrationTube to patient distanceFilm/Sensor speed – (Direct Digital or CR)
49Collimation, Collimation, Collimation Small fields give lower dose (and less scatter, therefore better image)Avoid more radiosensitive areas - e.g. gonads, female breastPosition carefully.Cover only the area needed
50Collimation, Collimation, Collimation Optimal collimation will result in :Lower patient doseLower occupational doseImproved image quality
51Tube Voltage (kV) – Intra-oral Higher kV (Quality) = lower skin dosetrade off = less contrast
52Low energy radiation = patient skin dose for no diagnostic value. FiltrationLow energy radiation = patient skin dose for no diagnostic value.Added filtration = lower patient skin doseIncreases beam qualitytrade off = less contrast
53Minimum Filtration 70kVp 1.5 mm Al> 70kVp 2.5 mm Al<1.5 mm Al – Filtration must be increasedAlso possible to have too much filtration.
54Tube to Patient Distance or Focus to Skin Distance (FSD) Greater FSD = lower patient doseGreater FSD = less magnification (so fewer distortions).
55Digital SensorsHigher doses = clearer imagesLower doses = noisier imagesEasy to not optimise doses as it is not so obvious when overexposure occurs.But underexposure results in grainy images.In our experience CR is slightly higher dose than filmDR is lower dose than film and CR
57There are no patient dose limits!!! Whilst there are no dose limits set for patient exposures, various surveys conducted over the past 25 years indicate a wide variation in doses for the same examination.It is therefore considered that there is significant scope for improvement in the optimisation of patient protection.
59Conclusion Justify – Optimise – Limit Time – Distance - Shielding CollimateChoose Correct Voltage & DoseUse the handover procedureRemember to Consult your RPA, they will give you Relevant Protection Advice – if in doubt ASK.
60Management of Radiation Protection in this Trust
61In This TrustRadiation Safety Policy is embedded into the general Health & Safety Policy CP137Radiation Physics website contains additional guidance:Staff & Patient PregnancyDiagnostic Reference LevelsDose Investigation LevelsDuties of the RPSPersonal Dose MonitoringLocal Rules
62Help … Radiation Protection Advisers Rad’n Prot’n Team X-Ray engineers John Saunderson – xCraig Moore – xRad’n Prot’n TeamAndrew Davis, Dave Strain, Tim Wood – extX-Ray engineersAndy Patchett & team – Medical Physics - HRI ext. 5756Oncology Physics TeamSean McManus and Co. xRadiation Protection websiteTrust Policy CP137