Part No...., Module No....Lesson No

Part No...., Module No....Lesson No
Module title Optimization of Protection in Computed Tomography (CT) Part …: (Add part number and title) Module…: (Add module number and title) Lesson …: (Add session number and title) Learning objectives: Upon completion of this lesson, the students will be able to: … . (Add a list of what the students are expected to learn or be able to do upon completion of the session) Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.) Duration: (Add presentation time or duration of the session – hrs) Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate) References: (List the references for the session) IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Introduction The subject matter: CT scanner and related image quality considerations The importance of the technological improvement made in this field The quality criteria system developed to optimize the CT procedure Background: medical doctor, medical physicist Explanation or/and additional information Instructions for the lecturer/trainer IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Topics CT equipment and technology Radiation protection rules and operational consideration Quality criteria for CT images Explanation or/and additional information Instructions for the lecturer/trainer IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Overview To understand the principles and the technology of CT To be able to apply the principle of radiation protection to CT scanner including design, Quality Control and dosimetry. Lecture notes: ( about 100 words) Instructions for the lecturer/trainer IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Optimization of protection in CT scanner
Part No...., Module No....Lesson No Module title Optimization of protection in CT scanner Topic 1: CT equipment and technology Part …: (Add part number and title) Module…: (Add module number and title) Lesson …: (Add session number and title) Learning objectives: Upon completion of this lesson, the students will be able to: … . (Add a list of what the students are expected to learn or be able to do upon completion of the session) Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.) Duration: (Add presentation time or duration of the session – hrs) Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate) References: (List the references for the session) IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Introduction Computed Tomography (CT) was introduced into clinical practice in 1972 and revolutionized X Ray imaging by providing high quality images which reproduced transverse cross sections of the body. Tissues are not superimposed on the image as they are in conventional projections The CT provides improved low contrast resolution for better visualization of soft tissue, but with relatively high radiation dose, i.e. CT is a high dose procedure

Computed Tomography CT uses a rotating X Ray tube, with the beam in the form of a thin slice (about mm) The “image” is a simple array of X Ray intensities, and many hundreds of these are used to make the CT image, which is a “slice” through the patient

The CT Scanner

A look inside a rotate/rotate CT
Part No...., Module No....Lesson No Module title A look inside a rotate/rotate CT Detector Array and Collimator X Ray Tube IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Helical (spiral) CT If the X Ray tube can rotate constantly, the patient can then be moved continuously through the beam, making the examination much faster

Helical Scan Principle
Part No...., Module No....Lesson No Module title Helical Scan Principle Scanning Geometry Continuous Data Acquisition and Table Feed X Ray beam Direction of patient movement IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Helical CT Scanners For helical scanners, the X Ray tube rotates continuously This is obviously not possible with a cable combining all electrical sources and signals A “slip ring” is used to supply power and to collect the signals

A Look Inside a Slip Ring CT
Part No...., Module No....Lesson No Module title A Look Inside a Slip Ring CT Note: how most of the electronics are placed on the rotating gantry X Ray Tube Detector Array Slip Ring IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

New CT Features The new helical scanning CT units allow a range of new features, such as: CT fluoroscopy, where the patient is stationary, but the tube continues to rotate multislice CT, where up to 128 slices can be collected simultaneously 3-dimensional CT and CT endoscopy

Module title CT Fluoroscopy Real Time Guidance (up to 8 fps) Great Image Quality High Dose Rate Faster Procedures (up to 66% faster than non-fluoroscopic procedures) Approx. 80 kVp, 30 mA IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Multi slice CT collimation
Part No...., Module No....Lesson No Module title Multi slice CT collimation 5mm 2,5mm 1mm 0,5mm IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title 3D Stereo Imaging IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title CT Endoscopy IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

CT Scanner Generator X Ray tube Gantry High frequency, 30 - 70 kW
Rotating anode, high thermal capacity: 3-7 MHU Dual focal spot sizes: about 0.8 and 1.4 Gantry Aperture: > 70 cm of diameter Detectors: gas or solid state; > 600 detectors Scanning time: <1 s, s Slice thickness: mm Spiral scanning: up to 1400 mm

Image processing Reconstruction time:
s/slice Reconstruction matrix: 256x256 – 1024x1024 Reconstruction algorithms: Bone, Standard, High resolution, etc Special image processing software: 3D reconstruction Angio CT with MIP Virtual endoscopy CT fluoroscopy

Spiral (helical) CT Spiral CT and Spiral multislice CT:
Volume acquisition may be preferred to serial CT Advantages: dose reduction: reduction of single scan repetition (shorter examination times) replacement of overlapped thin slices (high quality 3D display) by the reconstruction of one helical scan volume data use of pitch > 1 no data missing as in the case of inter-slice interval shorter examination time to acquire data during a single breath-holding period avoiding respiratory disturbances disturbances due to involuntary movements such as peristalsis and cardiovascular action are reduced

Spiral (helical) CT Drawbacks Increasing of dose:
equipment performance may tempt the operator to extend the examination area Use of a pitch > 1.5 and an image reconstruction at intervals equal to the slice width results in lower diagnostic image quality due to reduced low contrast resolution Loss of spatial resolution in the z-axes unless special interpolation is performed Technique inherent artifact

Part No...., Module No....Lesson No Module title Optimization of protection in CT scanner Topic 2: Radiation protection rules and operational consideration Part …: (Add part number and title) Module…: (Add module number and title) Lesson …: (Add session number and title) Learning objectives: Upon completion of this lesson, the students will be able to: … . (Add a list of what the students are expected to learn or be able to do upon completion of the session) Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.) Duration: (Add presentation time or duration of the session – hrs) Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate) References: (List the references for the session) IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Contribution to collective dose (I)
As a result of such technological improvements, the number of examinations have markedly increased Today CT procedures contribute for up to 40% of the collective dose from diagnostic radiology in all developed countries Special protection measures are therefore required

Contribution to collective dose (II)
100 200 300 400 500 70 75 80 85 90 95 Years CT scanners in clinical use in UK 3.3 Lumbar spine 7.1 Pelvis 7.2 Liver 7.6 Abdomen 7.8 Chest 2.6 Cervical spine 0.6 Orbits 0.7 Posterior fossa 1.8 Routine head Mean effective dose (mSv) Examination

Justification of CT practice
Justification in CT is of particular importance for RP CT examination is a “high dose” procedure A series of clinical factors play a special part Adequate clinical information, including the records of previous imaging investigations, must be available In certain applications prior investigation of the patient by alternative imaging techniques might be required Additional training in radiation protection is required for radiologists and radiographers Guidelines of EU are available

Optimization of CT practice
Once a CT examination has been clinically justified, the subsequent imaging process must be optimized There is dosimetric evidence that procedures are not optimized from the patient radiation protection point of view Examination CTDIw (mGy) Sample size Mean SD Min 25% Median 75% Max Head 102 50.0 14.6 21.0 41.9 49.6 57.8 130 Chest 88 20.3 7.6 4.0 15.2 18.6 26.8 46.4 Abdomen 91 25.6 8.4 6.8 18.8 24.8 32.8 Pelvis 82 26.4 9.6 18.5 26.0 33.1 55.2

Optimal use of ionizing radiation involves the interplay of the imaging process: Diagnostic quality of the CT image Radiation dose to the patient Choice of radiological technique

CT examinations should be performed under the responsibility of a radiologist according to the national regulations Standard examination protocols should be available. Effective supervision may aid radiation protection by terminating the examination when the clinical requirement has been satisfied Quality Criteria can be adopted by radiologists, radiographers, and medical physicists as a check on the routine performance of the entire imaging process

Part No...., Module No....Lesson No Module title Optimization of protection in CT scanner Topic 3: Quality criteria for CT images Part …: (Add part number and title) Module…: (Add module number and title) Lesson …: (Add session number and title) Learning objectives: Upon completion of this lesson, the students will be able to: … . (Add a list of what the students are expected to learn or be able to do upon completion of the session) Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.) Duration: (Add presentation time or duration of the session – hrs) Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate) References: (List the references for the session) IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Quality criteria for CT images: Example of good imaging technique (brain general examination)
Patient position Supine Volume of investigation From foramen magnum to the skull vertex Nominal slice thickness 2 - 5 mm in posterior fossa; 5-10 mm in hemispheres Inter-slice distance/pitch Contiguous or a pitch = 1 FOV Head dimension (about 24 cm) Gantry tilt 10-12 ° above the orbito-meatal (OM) line to reduce exposure of the eye lenses X Ray tube voltage (kV) Standard Tube current and exposure time product (mAs) As low as consistent with required image quality Reconstruction algorithm Soft Window width HU (supratentorial brain) HU (brain in posterior fossa) HU (bones) Window level HU (supratentorial brain) HU (brain in posterior fossa) HU (bones)

Quality criteria for CT images: brain, general examination
Image criteria Visualization of Whole cerebrum, cerebellum, skull base and osseous basis Vessels after intravenous contrast media Critical reproduction Visually sharp reproduction of the border between white and grey matter basal ganglia ventricular system cerebrospinal fluid space around the mesencephalon cerebrospinal fluid space over the brain great vessels and the choroid plexuses after i.v. contrast Criteria for radiation dose to the patient CTDIW 60 mGy DLP mGy cm

Image criteria for CT images: brain, general examination (visualization of)
Whole cerebrum, cerebellum, skull base and osseous basis Vessels after intravenous contrast media

Image criteria for CT images: brain, general examination (critical reproduction)
Visually sharp reproduction of the: border between white and grey matter basal ganglia ventricular system cerebrospinal fluid space around the mesencephalon cerebrospinal fluid space over the brain great vessels and the choroid plexuses after i.v. contrast

Quality criteria for CT images
A preliminary list of reference dose for the patient are given for some examinations expressed in term of: CTDIw for the single slice DLP for the whole examination Examination Reference doses CTDIw (mGy) DLP (mGy cm) Routine head 60 1050 Routine chest 30 650 Routine abdomen 35 800 Routine pelvis 600

Viewing conditions and film processing
It is recommended to read CT images on video display Brightness and contrast control on the viewing monitor should give a uniform progression of the grey scale Choice of window width dictates the visible contrast between tissues Film Processing Optimal processing of the film has important implications for the diagnostic quality Film processors should be maintained at their optimum operating conditions by frequent (i.e., daily) quality control

Module title Summary The CT scanner technology and the related radiation protection aspects The ways of implementing the quality criteria system related to the image quality and to dosimetry The importance of Quality Control Let’s summarize the main subjects we did cover in this session. (List the main subjects covered and stress again the important features of the session) IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Where to Get More Information (II)
Part No...., Module No....Lesson No Module title Where to Get More Information (II) Quality criteria for computed tomography, EUR report, (Luxembourg, EC), Radiation exposure in Computed Tomography; 4th revised Edition, December 2002, H.D.Nagel, CTB Publications, D Hamburg IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

CT Dose Reduction Techniques
A Practical Approach

Outline CT Dose Units Effective Dose Dose Reference Levels
CT Dose Optimisation Techniques CT Dose Modulation Bismuth Shielding Breast Shields in Practice Summary

CT Dose Units CT Dose Index - measures Absorbed Dose in a CT phantom (mGy) CTDIw = CTDI . tissue weighted factors CTDIvol - weighted average of CTDI from within a phantom and corrected for pitch or table increment DLP = CTDIvol (mGy) . L (mGy.cm) Where L = Scan Length Allows us to calculate Dose Effective dose – Estimate of Stochastic Radiation Risk Effective Dose (mSv) = DLP . CF Where CF is the conversion factor from IRCP table Takes Organ Sensitivity weighting factors into account Some CT dose units you need to be familiar with - CT dose index measures absorbed dose in a phantom (mGy) and was originally used for CT QA – it is not the patients dose - CTDI w – CTDI multiplied by organ weighted factor –available from icrp table - CTDIvolume is the tissue weighted average of CTDI from within a phantom and corrected for pitch or table increment - DLP is simply CTDIvol times Length of scan in cm - Effective dose is an estimate of stochastic radiation risk and allows us to compare CT with other modalities in mSv Effective dose is DLP multiplied by a conversion factor which take into account multiple organ sensitivity for specific body areas

103 ICRP Tissue Weighting Factors
Tissue Weighting ICRP 2007 Gonads 0.08 Bone Marrow (Red) 0.12 Colon Lung Stomach Breast Remainder Bladder 0.04 Liver Oesophagus Thyroid Skin 0.01 Bone surface Brain Salivary Glands Total 1 Adapted from an adult anthromorphic phantom Used to calculate effective dose to patients From the annals of the icrp publications 2008 These are the weighting factor used by the physicist to work out accurate effective dose ICRRP 103, 2008

Effective Dose Conversion Table
Effective Dose = DLP . CF Body Region Conversion Factor (mSv mGy-1 cm-1) Head 0.0023 Neck 0.0054 Chest 0.017 Abdomen 0.015 Pelvis 0.019 Normalised values of effective dose per dose length product over various body areas – an assessment for effective dose - able to be used for all vendors From the European guidelines on quality criteria for computed tomography 1999 Ref. European Guidelines on Quality Criteria for Computed Tomography EUR 16262, May 1999

CT Radiation Sources US Radiation sources to Population From NCRP Report No. 93 CT is 13% of medical x-ray exams, but accounts for 70% of medical dose (Lee, 04) In Australia CT accounts for 50% of all medical radiation dose (06-07) ARPNSA looking at establishing national DRLs - In the US CT accounts for 13% of medical x-ray exams but is responsible for 70% of all medical dose - What about Australia? In a study conducted by the Australian Radiation Laboratory CT had become the major if not the main contributor to doses in diagnostic radiology, they also Estimated that CT accounted for 50% of total medical radiation dose in -At the moment Australia doesn’t have any regulations on CT dose even though UK and US have had DRLs since 2000 - However the Aust Radiation protection and nuclear safety agency are Planning a new survey for MDCT doses in 2010 With the intention of developing national DRLs

DRL’s Dose Reference Level DRLs allow us to:
A reference level of dose likely to be appropriate for average sized patient undergoing medical diagnosis and treatment DRLs allow us to: Compare CT dose in mSv with other Modalities Compare our practice with other centers Realise if we have a certain margin for Optimisation Detect abnormal situations with high radiological risk to the patient -What are they and what advantage do they have? - Australian Radiation Protection and Nuclear safety agency defines DRL as a reference level of dose likley to be appropriate for average sized patients undergoing medical diagnosis and treatment - DRLs allow us to: - Compare CT dose in mSv with other Modalities -Compare our practice with other centers -Realise if we have a certain margin for Optimisation -Detect abnormal situations with high radiological risk to the patient -DRLs encourage changes in work procedures by showing what is possible in other departments

Establishing DRLs How Published DRLs Reference
Audit dose reports for range of body sizes of each scan type Record DLP and CTDIvol Employ your in house Physicist or Radiation Safety Officer to develop DRLs - third quartile values of CTDIvol and DLP Published DRLs Reference NRPB data survey 1990 ACR Recommendations European Guidelines 16262 ICRP From a study done in Malaysia 2007 on trends in DRL and weight relation

Ref. European Guidelines on Quality Criteria for Computed Tomography
UK DRL Guide Examination Diagnostic Reference Level CTDI (mGy) DLP (mGy . Cm) Routine Head 60 1060 Face/Sinuses 35 360 Vertebral Trauma 70 460 Routine chest 30 650 HRCT 280 Routine Abdomen 780 Liver/Spleen 900 Routine Pelvis 570 Osseous Pelvis 25 520 This Is the national European guide to DRLs If we use the conversion factor of for heads it converts to approximately 1.8mSv - Ref. European Guidelines on Quality Criteria for Computed Tomography EUR 16262, May 1999

US Typical Effective Radiation Dose Values
mSv NON CT Head CT 1-2 Hand X-ray <0.1 Pelvis CT 3-4 Chest X-ray Liver CT 5-7 Mammogram Chest CT Barium Enema 3-6 Abdopelvis CT 8-11 Coronary Angio 5-10 Cardiac CT 5-12 Sestamibi Scan 6-9 US typical effective Radiation Dose values from the mayo clinic 06 Mayo Clinic, 06

What should we be Doing? Archiving Dose Reports
Employ Dose Reduction Techniques Ask your Radiologist’s to Accept more Noise in your Images Look at developing your own site related DRL’s

Dose Optimisation Techniques
Patient Positioning Scouts kV FOV and Filters Pitch Image Noise Rotation Time Dose Modulation So with dose reduction in mind I just wanted to go over some simple best practice techniques

Patient Positioning Take the time to position the patient in isocentre
Use different tilt Positions when scanning the head Reduces scan Volume Ensure the patient is flat in the Z plane This effects optimal dose modulation - Take the time to position the patient in iso center- you will get better image quality and speed up your post processing times - Use different tilt positions when scanning the head For Sinuses and F/B tilt chin up Brains and PTB tilt chin down to avoid orbits and reduce the scan volume, directly reducing DLP and Dose - Make sure the patient is flat in the Z plane as this gives optimal dose modulation and image quality. It also reduces potential high skin doses

Positioning and Dose Modulation
Correct Alignment can reduce dose up to 56% (Banghart, 06) Centered too high = Increased Dose Centered too low = Reduced Dose and Increased breast dose - Correct patient alignment can reduce dose by up to 56% - from a paper by banghart 2006 Centered Correctly the body will be truly representative of its actual size. -Centered Too High in the gantry the body will be magnified and therefore create higher mA’s -Centered Too Low in the gantry the body will be reduced and therefore will create lower mA’s . Centering error Excessive dose Dose too low

Tube Position for Scouts
Make sure that tube position is PA when scanning scouts Reference vendor user guide to find out tube home position Kv must be the same for the scout and scan acquisitions for optimal dose modulation - For best practice Make sure that you tube position for scouts is PA as this reduces breast, thyroid and orbital dose - If you are not sure of your tube position during a scout reference your vendor user guide -Remember that kV must be the same for the scout as the scan range for optimal dose modulation

kV kV and Dose have an exponential relationship by a factor of 2
Lower kV = better image contrast resolution Generally standardised at 120 kV Try using 100kvp for smaller patients on chest scans Isolated Extremities can be scanned at kV Cardiac Scan performed at 100kV for patients <180pds Use kV for Paediatrics When kV is increased from 120 to 140kV = 39% dose increase - KV and Dose have an exponential relationship by a factor of 2 Using Lower KVs improve image contrast but there can be a noise penalty and beam hardening artifact - For Most CT scans kV is standardised at 120 KV But I suggest try using 100kvp for chest on smaller patients 80-100kv is ample for all isolated extremities with the exception of metallic implants which require high Kv a German study published in 09 demonstrated a 39% decrease in dose for cardiac by using 100kv for all patients less than 185pds (83kg) - 80 and 100kv should be used on paediatric patients depending on size – you can ask your vendor for some reference techniques -Just remember when kv is increased from kv the patient receives a 39% increase in dose

FOV and Filters Always choose the smallest FOV possible for the body part being examined Use Appropriate Filters provided by vendor Bow tie Filters can reduce skin dose by 50% Reduce noise and Artifact Use Paediatric Filters if Available Post Processing Filters Neuro Cardiac - Always choose the smallest FOV possible of the body part being examined The Largest FOV will have more scatter, therefore increased dose - Use your vendors filters they are designed to reduce patient dose Bow tie filters can reduce skin dose by up to 50% and also reduce noise and artifact - Use paediatric filters where avaliable - Post Processing filters don’t directly change the patients dose but they can be used to prompt radiologist to accept a higher noise levels in their images Centering error Excessive dose Dose too low Ref:

Pitch Pitch = table increment per rotation /beam collimation
Inversely Proportional to patient dose Larger Pitches Lower Radiation Dose Faster Scan times More image Noise Decreased Resolution Paediatric scans should have pitch of -We all know that pitch equals table increment per 360 rotation divided by beam collimation -Pitch is inversely proportional to patient dose By increasing the pitch from 1 to 1.5 produces a 33% reduction in dose - Larger pitches produce lower radiation dose, Achieve faster scan times but produces more image noise, decreased spatial resolution and helical artifact - Paediatric protocols should be set with pitches approximating between with the exception of PTB, extremity’s and where high detail is needed

Image Noise Noise is related to Dose Overcoming Noise
Increase MPR Thickness Use Post Processing Filters Use Appropriate Algorithms Ask Radiologists to accept more image noise Phantom B (40 mAs) Phantom A (80 mAs) A B - Noise is directly related to dose If mAs is halved then using this formula we expect to see a 40% increase in noise (images a and b) By accepting more image noise we can reduce scan dose - To overcome noisy images you can Increase your mpr thickness Use post processing filters and appropriate algorithms - Ask your radiologists to accept more image noise – especially for KUB and multiple coverage examinations

Rotation Time Rotation Time is related to dose in a linear fashion
Trade off with image noise Shorter Rotation Time Advantages Linear decrease in dose Faster scan time Less motion/breathing artifact Use Short Rotation times for Paediatrics 0.4s RT (200mAs) - Rotation time is related to dose in a linear fashion Decreasing RT from 1s per rotation to 0.5s per rotation = a 50% dose reduction - However the trade off is image noise (demonstrated in these images) - BY using short rotation times we produce a linear decrease in patient dose Faster scan times And less motion artifact - I recommend using short rotation times for paediatrics 1s RT (200mAs)

Dose Modulation Scanner adjusts the Xray tube mA automatically with changes in patient anatomy during the scan and from patient to patient Produces reduced dose scans without image quality compromise - Dose modulation is where the Scanner adjusts the X-ray tube mA automatically with changes in patient anatomy during the scan and from patient to patient - Produces reduced dose scans without loss in image quality Uses rotational current modulation based on either 1 or 2 scouts (vendor dependant) Typically mA used in the PA projections are significantly lower than the Lateral (as seen in the graph) - Dose modulation should be used for all examinations where possible with the exception of extremities as it produces a significant reduction in dose Ref. Radiographic Journal ,2006

Advantages of Dose Modulation
More consistent signal to detectors Image quality is maintained at a constant level Tube Heat capacity conserved Reduction in (photon starvation) streak artefact Dose Optimisation Dose Reductions from 10-50% Able to set Reference or noise levels Some vendors allow you to cap a max and min mA

Bismuth Shielding Shielding that can be used on in plane MDCT scanning
Has been shown to reduce radiation dose to skin and superficial organs without compromising image quality Reduces Primary beam Attenuation - Shielding that can be used on in plane MDCT scanning - Has been shown to reduce radiation dose to skin and superficial organs without compromising image quality - Reduces Primary beam Attenuation Image from a study on bismuth shielding placement on phantoms 2006 Ref. Medscape.com

Bismuth Breast Shielding
Used to Reduce unwanted radiation to the breast without degrading image quality Can reduce dose to breast from 43-73% for Thoracic scans - Bismuth Shielding is Used to Reduce unwanted radiation to the breast without degrading image quality -A paper from the journal of applied research in sept 06 found that chest wall or breast dose was reduced by 43-73% for thoracic scans based on an anthromorphic phantom A more recent study by yilmaz et al in 2007 from saw bismuth shielding reduce breast dose by % with no significant image degradation. Ref. Medscape.com

Breast Shielding In Practice
Patient Selection All Females of child bearing age ( <50yrs ) Where the anatomical Thorax is being scanned Shield Parameters Attenurad Bismuth Shield 0.06mm Pb 0.675cm offset – applied to each side Covered in plastic for cleaning and reuse At Western Health We have only just started using bismuth breast shielding so we decided to start simple - Patient selection was determined to be All Females of child bearing age ( <50yrs ) and Where the anatomical Thorax is being scanned - Shield Parameters we use an attenurad bismuth shield – 0.06mm PB equivalent 0.675cm offset foam is for optimal use of shield as recommended by the retailer (applied to each side so shield cannot be use the wrong way) covered in plastic for easy cleaning and reuse -In the next couple of months we will review the breast shield use and look at spreading it across a wider sample of patients

Breast Shielding Protocol
Shield Placement Top of shield is placed on sternal notch to cover breasts – curve round auxilla Shield is positioned after scouts have been performed -Breast Shield Placement Top of shield is placed on sternal notch to cover breasts – curve round auxilla - Our breast shield is placed on the patient after the scout acquisition – this is so dose modulation does not incorporate the shield into its mA calculations Ask your vendor for recommendations in bismuth shielding before purchasing

The Resultant Images 27 year old female ct chest with contrast
You can see the reduce in dose to the breasts with increased noise

Other Bismuth Applications
Ask your Vendor if Bismuth Shielding is compatible with your scanner Paediatric Breast Shielding Thyroid and Eye Shield - Ask your Vendor if Bismuth Shielding is compatible with your scanner when using dose modulation – they can also source you a shield distributor that is recommended for use on your scanner - Paediatric Breast Shielding can be purchased for different ages and with different thicknesses available for girls who have not undergone breast development - Bismuth Shielding can also be used for the thyroid and eyes Bismuth Shielding has also been found to not only reduce breast dose but reduce dose to others organs covered by the shield There is also evidence to suggest that bismuth shielding reduces dose even if the body area covered isn't under examination – useful for paeds (eg using thyroid, and breast shields when scanning the head) Ref. Impactscan.org

Summary Know your CT dose Units Audit CT Doses Archive Dose Reports
Think about possible site related DRL’s Review Dose Optimisation Techniques Use Dose Modulation where possible Ask your Radiologists to accept more image noise Use Shielding if available

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