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Transcript
PEDIATRIC RADIOGRAPHY The Role of The Radiographer in Dose Reduction for Paediatrics Cynthia Cowling ACR, B.Sc. M.Ed Director of Education ISRRT Development Leader, Radiation Sciences Central Queensland University, Australia 2 Outline • • • • Traditional role and techniques Role in CT Dose Reduction Implications for Interventional Dose implications in the move from Analog to digital • Some specialized activities 3 The pediatric patient always presents with unique problems for the radiographer • • • • • Keeping still Use of restraining devices Response to verbal direction Use of shielding Role of the family Use immobilization devices judiciously Capture the attention of the child 5 Other Devices • • • • • • • Tape (be careful not to hurt skin) Sheets, towels Sandbags Radiolucient sponges Compression bands Stockinettes Ace bandages Radiation Protection • • • • • • ALARA Proper immobilization Short exposure time Limited views Close collimation Lead aprons and half shields Differences children and adults • • • • • Mental development Chest and abdomen the same circumference in NB Pelvis - mostly cartilage Abdominal organs higher in infants than older children Hard to find ASIS or Iliac Crest in young child, can center 1 inch above umbilicus (bellybutton) • Exposure made as baby takes a breath to let out a cry Dose reduction in CT Use Radiologists and radiographers must create an essential partnership It is the Radiographer who UNDERSTANDS and OPERATES the equipment All CT sites should cooperate; start reduction and validate results 9 Essential features • • • • Dose should be age and weight specific Dose should be customized to pathology Number of follow ups should be scrutinized Software features should be used if possible – Image enhancement – Modulation of mAs 10 Working with the radiologist, the radiographer… • Starts with standard protocol and then reduces to provide acceptable image • Screens all requests, re protocol and suitability of request • Attempts to narrow down area of interest 11 Interventional Procedures • Increased because of immediate risk benefit for child (not undergoing surgery) • However, not much consideration given to long term stochastic effects 12 Collaboration makes a huge difference • Example from Hospital for Sick Children, Toronto Canada • In Angio CT the TEAM was able to reduce dose from 3 mSev to 0.8 mSev as standard for typical Angio CT exam for child 13 Dose Optimization in CT • kVp – decrease kVp, decrease dose, increase image noise, non-linear – Ex. 140 kVp 80 kVp (Siegel M et al, 2004) dose by 78% • mAs – decrease mAs, decrease dose, increase noise, linear – Ie. Halve mAs, Halve dose • Pitch, length of scan, gantry cycle time Cardiac Angiography CT Protocol • Weight-based protocol 1. IV injection of contrast 2. Set parameters: • Tube Voltage: 80 kVp • Gantry Rotation Time 0.4 s • Pitch 0.9 3. Variable parameters: Vary mAs According to body weight • - <5 kg: 70 mAs [Newborn phantom] • - 5-25 kg: 80 mAs [1-, 5-year old phantom] • - 25-50 kg: 90 mAs [10-year old phantom] • - >50 kg: 100 mAs 4. Scan Coverage • Only area of interest Conclusions • New protocol/equipment exposes patients to less radiation than previous set-up • Doses are less than 1 mSv across all phantoms ~75% decrease from previous protocol • Images are of diagnostic quality • Project is a good illustration of the utility we have at Sick Kids -> Easily determine radiation risk from various procedures with Moving Forward • This study was a general view of the exam • Study Clinical assessments to: – Collect data on what scans are used to diagnosis for – Percentage diagnosis yield – Percentage of cases that would have benefitted from lower/higher dose – Can we tighten dose optimization further Other Areas attempting dose reduction Scoliosis series 18 EOS 1- Takes two simultaneous digital EOS planar radiographs in the standing position with very low dose : 2D • 2 D 2- Creates a three dimensional sterEOS bone envelope weight bearing image : 3D 3 D Scanning process Collimated detector Collimated X Ray beam linear detector Linear scanning of a fan-shaped collimated X ray beam from 5 cm to 180 cm (whole body) No vertical divergence of X rays No scatter detect SNR increased Allows for lower dose ++ scanning Dose & Image quality Current practice : - Scattered radiation accounts for more than 80% of the X-ray flux passing through the patient - This noise reduces detectability and therefore a higher dose is required to maintain image quality Clinical impact of dose : M. Doody et. Al., « Breast Cancer Mortality After Diagnostic Radiography », Spine, Vol. 25, No 16, pp 2052-2063 Retrospective study on mortality due to breast cancer (women followed for scoliosis using spine X-Rays) : –5466 women followed between 1912 and 1965. Average of 25 radiographs (~0.11 Gy) => Risk of death due to breast cancer is 69% higher than what is encountered in general population. – In a linear scanner such as EOS, the detector geometry prevents more than 99.9% of the scattered radiation from entering the detector – EOS allows for a dose reduction up to 10 times compared to CR 21 Low dose & High Image Quality EOS requires less dose (Montreal study on spine) EOS 11% Fuji 100% EOS lowers dose by over 89% • Dose reduction x9… …With improved or equivalent image quality (97%) • High dynamic of image (16 bits, > 30 0000 Levels of Gray). EOS Non EOS/Dose x10 • Digital images, DICOM format • Single exposure for multiple exams • Pixel size 254µm Why Low Dose? Slot Scanning Technology – No scatter detected, Noise suppressed Allows for Lower Dose Charpak Nobel Prize Winning Detector – Detector amplification : Photon gaz cascade, High gain signal, sensitivity maximized Automatic internal gain adjustment – Dynamic range outperform other digital imaging technology (30,000 gray levels) – Available for any patient! Analog to Digital, Dose implications • Requires changes to radiographer’s knowledge base • Radiographers work practice must change to ensure high quality images • Must be more aware of dose since automation and image acquisition does not provide feedback in image production especially key effects of mAs and kVp • Radiographer must work as part of Team to ensure adherence to ALARA • QC always critical 24 Cont.. • Positioning can be more critical, aligning to detectors • Manual techniques may be required to produce optimum quality • Post processing as a method of enhancing image should be discouraged • Exposure creep must be avoided (any more than 4% unacceptable) ADVANTAGE provides statistical evidence of exposure factors and dose 25 How the profession can improve dose reduction • Increase awareness through membership in initiatives such as Image Gently • Provide retraining opportunities • Make use of publications such as ICRP • Participate in Clinical Audits • Actively work collaboratively with radiologists and physicians 26 For Example • In Ontario, Canada, Radiographers are regulated by the College of Medical Radiation Technologists of Ontario (CMRTO) and • Healing Arts Radiation Protection Act (HARP) which controls and identifies who can order and operate x ray equipment 27 Recommendations • HARP should require that prescribing or requesting a CT be permitted only by individuals who have appropriate clinical knowledge and training in radiation protection • All persons operating CT equipment or devices take a radiation safety course documented by a certificate of credentials – 200% increase in CTs in Ontario between 1996-2006 28 Enhancing Radiation Protection in Computed Tomography for Children Module two Image Gently www.imagegently.org 29 TWO KEY POINTS TEAM WORK TRAINING T E A M W O R K 30 Many Thanks and Acknowledgements to • Image Gently- Alliance for Radiation Safety in Pediatric Imaging • American Society of Radiologic Technologists-ASRT • Ellen Charkot, Director Imaging Services Hospital for Sick Children, Toronto Canada • Lori Boyd, Director of Policy College of Medical Radiation Technologists of Ontario, Canada (CMRTO) • Marie De La Simone, biospace med, Paris France • International Society of Radiographers and Radiological Technologists (ISRRT) • Maria del Rosario Perez, WHO 31