2014 version 21/04/2017

First FRCR Examination in Clinical Radiology General Radiation Protection (3h) John Saunderson Radiation Protection Adviser 21/04/2017

General Radiation Protection 21/04/2017

Medical and Dental Guidance Notes A good practice guide on all aspects of ionising radiation protection in the clinical environment “an essential reference book for all those working with ionising radiation in medical or dental practice, including medical and dental staff, radiographers, scientific and technical staff, and their employers.” 240 pages, £20 (discount for bulk purchase!) Buy from http://www.ipem.ac.uk 21/04/2017

Medical and Dental Guidance Notes 1. General measures for radiation protection 2. Radiation protection of persons undergoing medical exposures 3 - 4. Diagnostic & interventional radiology 5 - 6. Dental radiology 7- 9. Radiotherapy 10-18. Nuclear medicine and other uses of radioactive materials (+ Appendices 1 - 21) 21/04/2017

Radiation protection of the patient Justification -  Optimisation -  Limitation - X 21/04/2017

Ways to Optimising Patient Doses in Radiology minimise exposure time minimise radiation field size maximise tube voltage (kV) maximise beam filtration maximise tube to patient distance (FSD) minimise pulses per second minimise acquisition images minimise use of CT have a good quality assurance programme

OPTIMISATION Field Size Don’t irradiate more tissue than necessary Larger fields = larger doses to patient larger doses to staff (from scattered radiation) more scatter, resulting in more blurred images Some examples of poorly collimated paediatric chest radiographs

OPTIMISATION Exposure Time Don’t use X-rays at all if other non-radiation techniques can reasonably be used Don’t irradiate for longer than necessary If you are not looking at the monitor stop screening Use the freeze frame facility whenever appropriate

OPTIMISATION X-Ray Tube Voltage (kV) (more detail in lecture 4) On some sets kV can be selected by the operator. On fluoroscopy sets it is normally selected automatically, but different user selectable settings will affect how the automatic kV works. Higher kV radiation is more penetrating, so lower intensity beam into patient required to give same intensity out of patient to imager

From NIST Physical Reference Data (http://physics. nist 21/04/2017

Photoelectric Absorption   m x Z3 / E3  = linear attenuation coefficient for PE effect m = mass density (kg/m3) Z = atomic number E = photon energy 21/04/2017

Compton Scattering   m x e / E  = linear attenuation coefficient for PE effect m = mass density (kg/m3) e = electron density (e- per kg) [Z/A] E = photon energy 21/04/2017

21/04/2017 From NIST Physical Reference Data (http://physics.nist.gov/PhysRefData/XrayMassCoef/cover.html)

OPTIMISATION X-Ray Tube Voltage (kV) (continued) Higher kV radiation is more penetrating, so lower intensity beam into patient required to give same intensity out of patient to imager Therefore, higher kV = lower patient dose e.g. changing up from 90 to 110 kV may lead to a 26% reduction in skin dose changing down from 90 to 70 kV may lead to a 62 % increase in skin dose So at lower kV values the threshold for erythema can be reached in a shorter screening time On some sets “low dose mode” forces the X-ray set to use higher kV settings, and “high contrast mode” forces it to use lower kV settings.

OPTIMISATION X-Ray Tube Voltage (kV) (continued) But, because a higher kV beam is more penetrating then it will also less contrast between different materials Therefore, higher kV = less contrast Example – a 1 mm wire in the trunk, comparing 90kV to 110kV beam Skin dose 26% lower for 110 kV Effective dose 10% lower for 110 kV Contrast 15% higher for 90 kV You must have sufficient contrast to see what you need to in order to perform the clinical procedure, but a higher than necessary contrast can result in a higher risk of patient skin reactions, a higher risk of cancer induction in patients and staff, and a higher risk of exceeding your eye or other dose limit which could prevent you working with X-rays until the following year.

OPTIMISATION Beam filtration (more detail in lecture 4) All X-ray sets must have a metal filter (typically around 2 mm of aluminium) to remove very low energy X-rays which would never penetrate the patient and reach the imager, but would significantly increase the dose to the patient. Most modern fluoroscopy sets also have removable copper filters of a few tenths of a millimetre built into the X-ray tube housing. On some fluoroscopy sets the added copper filtration can be selected by the operator. On others it is normally selected automatically, but different user selectable settings will affect how much filtration is automatically driven into the beam.

OPTIMISATION Beam filtration (continued) More filtration effectively means the average energy of the X-rays is higher, and so with more filtration the beam is more penetrating. In exactly the same way as higher kV beams give lower patient skin dose but also lower contrast, more filtration will do exactly the same. On some sets “low dose mode” forces the X-ray set to use extra copper filters, and “high contrast mode” forces it to use no copper filter. Example – a 1 mm wire in the trunk in a 90kV beam, comparing no copper filter with using a 0.1 mm copper filter Skin dose 29% lower with 0.1 mm copper filter Effective dose 4.3% lower with 0.1 mm copper filter Contrast is 4.5% higher for no copper Use the maximum filtration you can while still maintaining adequate image quality for the task you are undertaking.

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Transmission through 10 cm tissue 80 keV  16 % 60 keV  13 % 50 keV  10 % 40 keV  7 % 30 keV  2 % 20 keV  0.04 % 15 keV  0.000008 % 10 keV  10-21 % 21/04/2017

Minimum Filtration General tube  2.5 mm aluminium Mammography  0.03 mm molybdenum or 0.5 mm Al Dental ( 70kVp)  1.5 mm Al Dental (> 70kVp)  2.5 mm Al 21/04/2017

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Tube to Patient Distance 21/04/2017

Tube to Patient Distance Greater FSD = lower patient dose e.g.  from 50 to 70 cm   49% skin dose Greater FSD = less magnification (so fewer distortions) Tube to patient distance never < 30cm, preferably > 45cm for chests > 60 cm .

Tube to Patient Distance In fluoroscopy always have the patient as close to the imager as possible as far from X-ray tube as possible Greater FSD# = lower patient dose e.g.  from 50 to 70 cm FSD   49% skin dose Greater FSD = less magnification (so fewer distortions) (# FSD = focus to skin distance, where the focus is the source of the X-rays inside the X-ray tube)

One of the main causes of unnecessary radiation injury to patients is bad positioning, with the patient (or part of the patient such as their arm) too close to the X-ray tube Approximate screening times to reach erythema threshold dose (At 20 – 100 mGy/min, 70 cm FSD) 70 cm from focus = 20 - 100 mins 50 cm from focus = 10 -50 mins 30 cm from focus = 3 - 18 mins

Fluoroscopy Only expose when looking at monitor Keep patient close to image intensifier and far from tube (at least 30 cm from tube for mobile, 45 cm for static) Use low dose setting, unless image unacceptable (i.e. high kV, high filtration) Magnification increases dose rate to skin (although a smaller area irradiated) Cone down where practicable Special care if skin dose likely to exceed 1 Gy. 21/04/2017

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Entrance Dose Rates for Standard Phantom 21/04/2017

Time to Reach 2 Gy for Standard Phantom 21/04/2017

Skin dose rate (mGy/min) Field size HRI CP1 Siremobil Low dose High dose Cont. Low mA high mA Pulsed 38 cm 17 19 25 cm 23 40 23cm 13 10 5 17 cm 28 49 12 6 Max. 125 70 Remedial level: 50 mGy/min for largest field (standard patient) Suspension level: 100 mGy/min (standard patient) 21/04/2017

Frame rate / Pulses per second Fewer pulses per second = less dose e.g. 15 pps gives half the dose of 30 pps Fewer pulses per second = potential blurring if there is patient/organ movement Use the lowest frame rate you can while still maintaining adequate image quality for the task you are undertaking.

Fluoroscopy Dose Modes “Low dose” higher kV (lower mA) more copper filtration therefore, lower contrast “High contrast” lower kV (higher mA), less copper filtration therefore higher dose 21/04/2017

Screening and Acquisition Screening uses a low dose rate, allowing movement to be observed. Acquisition/spot images use a higher radiation dose for a short time to reduce noise in the image and take a high quality snapshot. Only use acquisition when you really need the extra image quality, and then use sparingly.

Screening dose vs Acquisition dose e. g. HRI CP1, 20 cm field size, 18 Screening dose vs Acquisition dose e.g. HRI CP1, 20 cm field size, 18.5 cm Perspex phantom Screening 77 kV, 2.2 mA Skin dose rate  19 mGy/min (Erythema threshold  105 min) Digital acquisition 80 kV, 475 mA, 32 ms Skin dose  2.5 mGy/image (Erythema threshold  800 images) So in this example, in terms of patient skin dose 1 spot image  8 seconds of screening

General Good Practice in Fluoroscopy Only expose when looking at monitor (if you are not then the radiation dose to the patient and staff has no benefit) Keep patient close to image intensifier and far from tube (at least 30 cm from tube for mobile, 45 cm for static) Use low dose setting, unless image unacceptable Magnification increases dose rate to skin (although a smaller area irradiated, effectively more dose is squeezed into a smaller area to get a bright enough image) Cone down where practicable Take special care if skin dose is likely to exceed 1 Gy, as erythema may be caused#.                                       Note, higher patient dose also means higher dose to you and other staff in the X-ray room (# some sets display “skin dose”, but this assumes an average size patient in a standard set up. So “1 Gy” displayed could be above the 2 Gy erythema threshold for a real patient.)

Here on 25/11/2014

Computed Tomography (CT) (Covered in more detail in Craig Moore’s lectures) High dose, so justification important Lowest mA practicable Minimum number of slices necessary Angulation of gantry can substantially reduce eye dose. 21/04/2017 .

Individual procedure doses

Individual procedure doses (UK averages) Conventional radiography CT Head 0.068 mSv C spine 0.03 Shoulder 0.011 Chest 0.014 T spine 0.38 L spine 0.6 Abdomen 0.43 Pelvis 0.28 Singel hip 0.087 Both hips 0.19 Femur 0.012 Knee 0.0002 Foot IVU 2.1 CT head 1.4 mSv CT chest 6.6 CT chest hi-res 1.2 CT abdomen 5.6 CT abdo-pelvis 6.7 CT chest-abdo-pelvis 10 Fluoroscopy Ba swallow 1.5 Ba follow 1.3 Ba enema 2.2 Coronary angiography 3.9 Femoral angiography 2.3 HPA-CRCE-012 - http://webarchive.nationalarchives.gov.uk/20140629102627/http://www.hpa.org.uk/webc/HPAwebFile/HPAweb_C/1287148001641

Comparing CT with general radiology

Computed Tomography (CT) (Covered in more detail in Craig Moore’s lectures) High dose, so justification important Optimise protocols (e.g. lowest mA practicable) Minimum number of slices necessary Angulation of gantry can substantially reduce eye dose. 21/04/2017 .

Chest ‘only’

Dose quantities in CT Computed Tomography Dose Index (CTDI, in Gy) Average dose inside the beam 21/04/2017

CTDIw = 1/3CTDI100(centre) + 2/3CTDI100(peripheral) Weighted CTDI100 CTDIw = 1/3CTDI100(centre) + 2/3CTDI100(peripheral) 21/04/2017

Dose quantities in CT Dose length Product (DLP, in Gy.mm) 21/04/2017

NRPB - W67 Doses from Computed Tomography (CT) Examinations in the UK - 2003 Review 21/04/2017

CT Dose Optimisation Don’t CT unless sufficient benefit Don’t use very thin inefficient slices if unnecessary Lowest mAs/slice for acceptable noise level Understand Dose Modulation systems and use where appropriate Largest pitch Shortest scan length 21/04/2017

Pregnancy (link from http://www.hullrad.org.uk) - can be downloaded from http://www.hpa.org.uk/webw/HPAweb&HPAwebStandard/HPAweb_C/1238230848780?p=1199451989432 (link from http://www.hullrad.org.uk) 21/04/2017

Radiation risks to the Embryo or Foetus Deterministic effects The radiation dose to the embryo or foetus that is likely to result from any diagnostic or interventional procedure in current use should present no risk of causing death, malformation, growth retardation or impairment of mental ability. Stochastic effects There is a increased risk of childhood cancer associated with irradiation in the womb

Pregnancy – Deterministic effects 21/04/2017

Radiation induced childhood cancer The risk is around 1 in 10,000 for a 1 milligray dose to the foetus The natural incidence of childhood cancer is around 1 in 500 The following slides give the range of foetal doses from common radiological procedures and the associated risks taken from the Health Protection Agency’s 2009 guidance. A few of particular interest in cardiology from these tables are Examination Typical foetal dose range Risk of childhood cancer per examination X-ray chest <0.01 mGy < 1 in 1,000,000 CT Pulmonary Angiogram 0.01 to 0.1 mGy 1 in 1,000,000 to 1 in 100,000 Nuclear medicine cardiac scans 1 to 10 mGy 1 in 10,000 to 1 in 1,000

Foetal doses and risk (1)

Foetal doses and risk (2)

Flow chart showing general principles Is pregnancy possible? No Proceed with examination Yes Flow chart showing general principles see HPA guidance for more detailed (but straighforward) advice on application (http://www.hpa.org.uk/webw/HPAweb&HPAwebStandard/HPAweb_C/1238230848780?p=1199451989432 ) Is the patient definitely or probably pregnant? Yes, possibly pregnant No Would it be reasonable to delayed the procedure until after delivery, or confirmed not pregnant? Yes Delay If pregnancy cannot be excluded, is this a low dose procedure? (i.e. < 10 mGy foetal dose) No Yes No, high dose Yes No Proceed with examination, taking any practical steps to minimise foetal dose consistent with the clinical purpose. Is the patient’s menstrual period overdue? Will procedure be within first 10 days of menstrual cycle? No Yes Proceed with examination Proceed with examination

e.g. CT pelvis CT pelvis & abdomen CT Pelvis, abdomen & chest Myocardial Tc-99m scan Whole body PET/CT scan . 21/04/2017

Inadvertent Foetal Exposure If this happens, either due to staff or patient “error” An investigation should be carried out in consultation with a Medical Physics Expert in accordance with Trust IRMER procedures The MPE can provide a dose and risk estimate The MPE can advice on whether the incident needs to be reported to the authorities under IRMER Risk from a diagnostic X-ray is small enough never to be grounds for invasive foetal diagnostic procedures for termination

Infants and Children Gonad shields should be used where relevant and practical Restrict field to essential area 21/04/2017

21/04/2017 From www.info.gov.hk/dh/diseases/CD/photoweb/RSVacutebronchiolitis-1.jpg

Infants and Children Gonad shields should be used where relevant and practical Restrict field to essential area Greater level of justification 21/04/2017

Infants and children Higher risk of inducing cancer than adults .

Probability of fatal cancer (Atom bomb “survivors”) From ICRP60 table B-12 0-19 y  24% per Sv (1 in 4,000 per mSv) 20-64 y  8% per Sv (1 in 12,000 per mSv) 0-90 y  10% per Sv (1 in 10,000 per mSv) i.e. children risk  3 x adult risk 21/04/2017

Also Use AECs Properly calibrated CR Low attenuation table tops, etc. (e.g. c-fibre) Quality assurance Good processing and viewing conditions DRLs 21/04/2017

End of part 1 21/04/2017

First FRCR Examination in Clinical Radiology General Radiation Protection Part II John Saunderson Radiation Protection Adviser 21/04/2017

General Radiation Protection Radiation protection of the patient including pregnancy, infants and children Medical and biomedical research Health screening Radiation protection of staff and members of the public Use of radiation protection devices. 21/04/2017

Medical & biomedical research Must be LREC approved If no benefit to individual - DOSE CONSTRAINTS If benefit to patient - INDIVIDUAL TARGET LEVELS of DOSE Risks must be communicated to volunteer Avoid pregnant women or children unless specific to study. Only one study a year for healthy volunteers. 21/04/2017

Health screening Medical Physics Expert must be consulted Special attention to dose Dose constraints 21/04/2017

e.g. is mammography screening of 40-49 year olds justified? Currently 50-64’s screened 300+ lives saved per year (UK) Between 0 and 2 in 1000 will have life extended if 40-49 screened For 50-64, 1 in 10 missed For 40-49, 1 in 4 missed 1 in 10,000 risk of inducing cancer (40-49) other “risks” 21/04/2017

Radiation protection of staff Controlled areas Time, distance, shielding lead aprons 21/04/2017

Leakage 21/04/2017

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Scatter Dose e.g. Lat. Lumbar spine No lead apron: 0.6 mGy @ 30 cm With 0.35 mm apron: 0.06 mGy @ 30 cm (Primary skin dose: 16 mGy) Public dose limit = 1 mSv  17 patients C&C constraint = 5 mSv  83 patients Staff limit = 6 mSv  100 patients. Films rather than patients? 21/04/2017

Scatter dose from typical coronary angiography at 1 m Higher scatter dose tube side, as scatter towards imager is partially absorbed by the patient

Doses Relative to Lum. Sp. Chest: x 0.02 Skull: x 0.04 Thoracic spine, pelvis: x 0.5 Abdomen: x 0.8 IVU: x 1.5 Ba. Enema: x 4.1 CT abdomen: x 5.9. 21/04/2017

Radiology Staff Protection Only essential staff in radiation area Protective clothing if not behind screen Close doors Minimum beam size (min. scatter) Never point primary beam at screen Use mechanical devices to support patients (unless …) Record where staff hold, rotate staff. 21/04/2017

Staff pregnancy IRR99 – dose limit to foetus of employee is 1 mSv during declared term of pregnancy For diagnostic radiology 2 mSv to abdomen  1 mSv to foetus 98% of imaging department staff in UK < 1 mSv/y effective dose (2005) Diagnostic & interventional X-Ray staff monitored > 1mSv/y (n=10,336) 1 in 150 radiographers 1 in 40 diagnostic radiologists 1 in 16 interventional radiologists 1 in 61 other clinicians monitored 1 in 100 nurses monitored 1 in 200 others monitored https://www.rcr.ac.uk/docs/radiology/pdf/Pregn ancy_Work_Diagnostic_Imaging_2nd.pdfhttps:// www.rcr.ac.uk/docs/radiology/pdf/Pregnancy_W ork_Diagnostic_Imaging_2nd.pdf 21/04/2017

Annual whole body occupational doses (UK 2005) Nuclear medicine (non-PET) staff monitored > 1mSv/y (n=677) 1 in 6 pharmacists monitored 1 in 2-3 nuclear medicine technologists or radiographers 1 in 17 scientists 1 in 10 clinicians 1 in 3-4 nurses 1 in 73 others monitored 2007 survey of PET staff (n=58) nearly 70% of staff > 1mSv/y mean dose of 1.9 mSv i.e. most pregnant PET staff will need to significantly alter work practice 21/04/2017

Radiation Protection of members of the public Walls, doors, etc. controlled areas . . . comforters and carers. 21/04/2017

Comforters and Carers 21/04/2017 "individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure” c.f. doses to patients in red book Highly unlikely for a single exposure. 21/04/2017

Comforters and Carers "individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure" "individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure” c.f. doses to patients in red book Highly unlikely for a single exposure. 21/04/2017

Comforters and Carers "individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure" "individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure” c.f. doses to patients in red book Highly unlikely for a single exposure. 21/04/2017

Comforters and Carers "individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure" "individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure” c.f. doses to patients in red book Highly unlikely for a single exposure. 21/04/2017

Comforters and Carers "individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure" Dose constraint required. 21/04/2017

Comforters and Carers e.g. parent holding a child being X-rayed not a nurse, care assistant, etc. if < 1 mSv public dose limit, not “C&C” 5 mSv dose constraint if pregnant 1 mSv dose constraint must be aware of the risk. "individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure” c.f. doses to patients in red book Highly unlikely for a single exposure. 21/04/2017

Radiation protection devices 21/04/2017

Guidance Notes Gloves, aprons eyewear Protect from scatter or transmitted radiation, NOT primary Must be marked with lead (Pb) equivalence & CE Body aprons Not less than 0.25mm Pb for up to 100kV Not less than 0.35mm Pb for over 100kV HSE assumes dose under apron is effective dose Gloves no less than 0.25mm @ 150kV Do not use half body aprons Hang carefully, never fold, Check at least annually by fluoroscopy. 21/04/2017

Transmission through Lead Aprons 0.25 mm Pb 60 kV, T = 1.5 % 90 kV, T = 9.5 % 120 kV, T = 17.5% 0.35 mm Pb 60 kV, T = 0.5 % 90 kV, T = 4.9 % 120 kV, T = 11.3 % 2 x 0.35 mm 90 kV, T  1.1 %

Light weight aprons Use materials with different Z and density than lead (e.g. tungsten, barium) Note kV of Pb equivalence! Sometimes just smaller & shorter! 21/04/2017

Thyroid shields Usually 0.5mm Pb Transmission = 2.5% @ 90kV Tissue or organ wT (2007) Gonads 0.08 Red bone marrow 0.12 Colon 0.12 Lung 0.12 Stomach 0.12 Bladder 0.04 Breast 0.12 Liver 0.04 Oesophagus 0.04 Thyroid 0.04 Skin 0.01 Bone surfaces 0.01 Brain 0.01 Salivary glands 0.01 Remainder 0.12 Usually 0.5mm Pb Transmission = 2.5% @ 90kV 21/04/2017

Eye Protection (1) Threshold for detectable opacities = 500 mGy to lens ICRP dose limit for lens of eye = 150mSv a year 20 mSv/y (averaged over 5 years) Glasses 0.75mm Pb Direct transmission 0.9% @ 90kV, but But in reality 13%-33% because of scatter around edges etc. Mask 0.1mm Pb Direct transmission 25% @ 90kV 21/04/2017

Eye Protection (2) Lead acrylic or lead glass screens Overhead screens typically 0.5mm Pb Direct transmission = 2.5% @ 90kV) But in reality 13%-66% because of scatter around edges etc. 21/04/2017

Hand protection Threshold for transient erythema = 2,000 mGy ICRP dose limit for hands, feet, skin = 500 mSv a year Gloves 0.5mm Pb (1.2% @ 90kV) 1.4 kg each Thin gloves 0.3mm at finger tip 39% @ 90kV

Gonad Protection (patient) Solid 2mm Pb 0.01% @ 90kV Flexible 0.5mm Pb 2.5% @ 90 kV 21/04/2017

Others 21/04/2017

Transmission through Other Materials Code 3 Pb (1.3 mm) 120 kV, T = 0.7 % 9” of red brick 120 kV, T = 0.04 % 2 x 10 mm plasterboard 120 kV, T  52. % 1” wood 120 kV, T = 86 % 5 mm plate glass 120 kV, T = 63. %

Fin 21/04/2017

Here on 2/12/2014 21/04/2017