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Radiation Protection in Paediatric Radiology

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Radiation Protection in Paediatric Radiology

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  1. Radiation Protection in Paediatric Radiology Radiation Protection of Children During Computed Tomography L06

  2. Educational objectives At the end of the programme, the participants should: • Recognize that CT is a relatively higher dose imaging procedure. • Understand dose management strategies for computed tomography in children. Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  3. Answer True or False • Reduction of kVp in CT reduces the dose. • CT contributes 60-70 % of the dose from radiological examinations in developed countries. • The same CT protocol used for children and adults will result in a higher dose to adults. Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  4. Contents • Overview of CT systems: SDCT and MDCT. • Dose levels in CT and risk attributable to paediatric CT. • Importance of application of justification in paediatric CT. • Optimization of image quality and patient dose in paediatric CT. • Selection of appropriate technical parameters. • Use of shielding devices in paediatric CT. • Dose management strategies in paediatric CT. • Requirements for staff: experience and training. Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  5. Computed Tomography • Computed tomography (CT) is the method that extends the clinical capabilities of X-ray imaging: • High contrast sensitivity for visualizing soft tissues. • Production of configurable data sets. • Three-dimensional (3D) representations • Multiplanar depictions • “Volume” CT • Dynamic (e.g. perfusion, cardiac) information • Tissue characterization (dual energy technology) • Advances in computed tomography (CT) technology have continued to improve existing and open new clinical applications. Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  6. Computed Tomography • Since 1972; then… Hounsfield Cormack Nobel prize for medicine 1979 Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  7. Computed Tomography • ..and now… Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  8. Modern CT Scanners • Modern CT scanners are 3rd generation, that is the tube and detectors rotate together around the patient • Slip ring technology allows for spiral hence volume scanning Principle of spiral CT. Patient is transported trough the gantry, x-ray tube traces spiral path around the patient when acquiring data M. Mahesh, MDCT physics, the basic technology, image quality and radiation dose, Wolters Kluwer, 2009 Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  9. Single Detector (SDCT) vs Multi-detector (MDCT) Computed Tomography SDCT and MDCT design. The difference is the presence of multiple-row detectors in the longitudinal direction with MDCT yielding multiple slice options for single rotation M. Mahesh, MDCT physics, the basic technology, image quality and radiation dose, Wolters Kluwer, 2009 Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  10. Multi-detector (MDCT) Computed Tomography MDCT detectors M. Mahesh, MDCT physics, the basic technology, image quality and radiation dose, Wolters Kluwer, 2009 Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  11. CT and Paediatric Radiology • The patient dose in CT is an important issue for children. • In some centres, the exposure factors used for scanning children are the same as for adults. • CT scanning contributes most to collective dose from exposures from medical imaging due both to relatively high dose per exam and to the increasing use of this modality. Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  12. Facts About CT… • Facts about CT… • 69 million CT examinations per year for all ages in USA in 2007. • Approximately 10% growth rate per year • 7 million CT examinations per year in children • 40-50 % increase in paediatric CT from 2005/06. • Up to 31% of paediatric body CT examinations are multiphase in some reports Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  13. The frequency of CT examinations is evenly distributed at all ages: 33% are performed in children under age of 10 Repeated examination: 30% of adults and children have three or more CT scans Facts About CT… METTLER, F.A., et al., J. Radiol. Prot. 20 4 (2000) 353-359 Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  14. CT as a Dose Contributor CT examinations: • comprise only 17% of all radiological examinations, but... • contributes to 49% of the effective dose all radiological examinations Mettler et al. Helath Phys 2008, 95:502-7 Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  15. Amount of Radiation Resulting From CT Frush D, et al, CT and Radiation Safety: Content for Community Radiologists www.imagegently.org Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  16. Why is this so? Radiography CT Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  17. Why is this so? Dose distribution* *in relative units Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  18. Risk of CT Examination • Unique consideration in children: • Life time to manifest the bioeffects • More radiosensitive tissues • Dose is considered cumulative over time • Risk is higher for females and younger age groups • From a single abdominal CT in paediatric age, lifetime estimated risk for fatal cancer is 1: 1000 - 1: 2000. Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  19. Risk Versus Benefit • Important to distinguish between individual risks and collective, public-health risks • The individual risks are small, so the benefit / risk ratio for any child will generally be very large, • …but the exposed population (~7.0 million children/yr in the US) is large • Even a very small individual radiation risk, when multiplied by a large (and increasing) number of children, is likely to produce a significant long-term public health concern Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  20. CT in Paediatric Radiology • The frequency of paediatric CT examinations has been increasing over the past 20 years • Reduced requirements for sedation and allowance of examination of younger, sicker and less co-operative children • Increased speed of acquiring diagnostic information • Increased number of multiple scans • Attention must be given to adapting protocols to suit children taking into account that they are more sensitive than adults Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  21. In Paediatric Radiology… • If identical CT head examination protocol is used: • Adult dose: 1.5 mSv • Child dose: 6 mSv Huda et al. Radiology, 1997, 203:417-22 Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  22. In Paediatric Radiology… • It estimated that between a third and halfof the examinations occurring have questionable indications. • Many are conducted using inappropriate technical factors. Frush, RSNA, 2006, Berenner Pediatr. Radio.l 32 (2002) 228 – 231, Oikarinen et al. Eur Radiol 19 (2009) 1161-5 Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  23. Justification and CT • It is very important that each examination is rigorously justified, thus… Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  24. Justification for CT: Practical Advice • Justify CT examination rigorously and eliminate inappropriate referrals. • Perform only necessary CT examinations. • Reduce the number of multiple phase scans. • Work to account for previous procedures. Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  25. Justification for CT: Practical Advice • Use referral guidelines and appropriateness criteria when available • Use alternative approaches, such as ultrasound, MRI where appropriate • Include justification in clinical audit Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  26. How to achieve the objective? • Respect age-specific pathology and its prognosis. • Consider potential contribution of the scan to patient management and outcome. • Consider the patient’s medical imaging record with respect to ionizing radiation Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  27. How to Achieve the Objective? • Respect cost and radiation exposure. • Replace CT by examination with no or with lower radiation exposure (e.g. US, MRI). • Delay/cancel follow-up examination unless a decision based on scan is needed now. Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  28. Optimisation and CT One size does not fit all... Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  29. Optimisation and CT For paediatric CT examinations, the use of specific radiographic technical parameters should be promoted as: • Child size the kVp and mA.  • One scan (single phase) is often enough.  • Scan only the indicated area. Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  30. General Recommendation • You must use paediatric protocols to reduce the dose for the same image quality as in adults • Make sure there are no inappropriate high (e.g. adult) parameter settings behind the name paediatric protocols • Plan paediatric scans according to patient’s size and age Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  31. Generic Requirements for Optimisation • Inform and prepare the patient and accompanying person(s). • Be familiar with CT dose descriptors. • Realise lower noise usually means higher doses; accept noise if scan is diagnostic. • Make sure operating conditions balance image quality and radiation exposure.  Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  32. Generic Requirements for Optimisation • Optimize scan parameters within the axial plane. • Optimize a set of tube current settings for paediatric examinations. • Optimize scan parameters for volume coverage. • Scan minimal length and minimise repeated scanning at identical areas. Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  33. Equipment, Protocol, Dose and Image Quality • In most children a tube voltage of 80–100 kVp will suffice, especially in children with a body weight <45 kg. • In adolescents, a tube voltage of 100 kVp for the thorax and 120 kVp for the abdomen is usually sufficient • Recent studies with phantoms suggest that the optimal tube voltage in children may be even lower (60kVp) at least for some indications Nievelstein, Pediatr Radiol, 2010 Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  34. Equipment, Protocol, Dose and Image Quality • Spiral or helical scanning is preferable in paediatrics as an entire volume is imaged • Short tube rotation times reduce movement artefacts and provide more detailed cardiac imaging • One main benefit for MDCT scanners is speed of acquisition rather than dose reduction Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  35. Equipment, Protocol, Dose and Image Quality • An increase in pitch can result in a shorter scan time and (in some scanner types) in a dose reduction • In modern MDCT scanners this may not be the best option (due to overranging) • If effective mAs is used, an increase in pitch will result in an increase in the tube current • Therefore, it is usually more dose efficient to keep the pitch as low as possible (<1) and if needed manually decrease the tube current Nievelstein, Pediatr Radiol, 2010 Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  36. Equipment, Protocol, Dose and Image Quality • Multi-slice scanners have potential to deliver higher dose • by having a wider beam irradiating a number of detector rows to achieve multiple slices simultaneously • as well as owing to more extensive clinical use • However.… Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  37. Equipment, Protocol, Dose and Image Quality • Strategies for dose reduction in MDCT: • Hardware improvements • Software improvements, as tube current modulation, image reconstruction algorithms, … Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  38. Equipment, Protocol, Dose and Image Quality • Modern scanners give automatic or semiautomatic correction of tube current (mA) for patient size (mA modulation). • Significant dose reduction (20–50%) without appreciative loss of image quality. Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  39. Equipment, Protocol, Dose and Image Quality • Image thickness: • Should be chosen depending on the size of the child and the application • Use maximal acquisition collimation (assuming this would result in scanning at lower mA) appropriate for specific diagnosis • Narrow collimation in MSCT and 1 mm slices on some SDCT result in a higher dose (increase in mAs to maintain image quality) Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  40. Equipment, Protocol, Dose and Image Quality 2. Pitch: • SDCT: a pitch factor 1.5 is recommended for most examinations • 25% reduction in dose compared with using a pitch of 1 • MDCT: reduction in dose due to greater pitch may not beachieved • tube current (mA) can beautomatically adjusted to keep the dose and noise the same Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  41. Equipment, Protocol, Dose and Image Quality 3. Tube potential (kVp) • There are few advantages to using a high tube potential (kV). • Without a reduction in tube current (mA) this leads to a significantly higher dose. • 100 kVp or 80 kVp is usually adequate for children. • Lowering of kVp enhances contrast • 10 kg patient transmits 3-4% while an adult transmits less than 0.1%. • Be aware that images with high noise, even if they do not look very crisp, may provide the diagnostic information. Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  42. Equipment, Protocol, Dose and Image Quality 4. Lower tube current (mA): • Lower tube current (mA) should be used for scanning kids. • High tube current is required only when there is a need for high image detail ( in low contrast settings) • Decrease of mA according to body diameter and use of exposure charts if AEC is not available (dose reduction 70-80%),Lucaya, et al, 2000, AJR 175:895-92 • Use of tube current modulation technology results indose reduction by 60% for paediatric scanning, Kalra et al, 2004, Radiology, 233:649-57 Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  43. Equipment, Protocol, Dose and Image Quality 5. Gantry Tilt • A straight gantry results in irradiation of a smaller volume of tissue compared with a tilted gantry and is recommended. • Exception: tilt is used to avoid unnecessary exposure of sensitive tissues, e.g. in brain CT for avoiding the orbits. Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  44. Equipment, Protocol, Dose and Image Quality 6. Scan Length • Scan the minimum length required and be restrictive in defining upper and lower limits. • Optimise scan parameters for volume coverage by using representative volume sample(s) when the entire volume is not needed (by sequential scans with gaps) to reduce dose-length product Vock and Wolf , Dose Optimization and Reconstruction in CT of children, in Radiation Dose from Adult and Paediatric MDCT, Springer, 2007 Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  45. Equipment, Protocol, Dose and Image Quality 7. Reconstruction Algorithm • Appropriate reconstruction algorithms, window levels and window settings should be used Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  46. Equipment, Protocol, Dose and Image Quality 8. Dose Indices • Protocols must be adjusted by the operator to take into account the patient's age and weight (size). • Newer scanners indicate the volumetric CT dose index (CTDIvol ) and Dose-length product (DLP) on the console (Requirement from IEC 60601-2-44). • This allows the user to automatically: • See the relative effect on dose owing to changes in kVp, mA, collimation and pitch, • Estimate the effective dose to patient. Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  47. Radiation Dose Indices for CT Dose displays on modern multislice scanners: • Volume CTDI (CTDIvol) • Dose Length Product (DLP) Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  48. Dose Indices for CT • CTDI is a local per scan dose and is dependent on kVp, mAs and slice collimation. • DLP is an integral dose over the scan length and number of series and depends on pitch and dose Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  49. Computed Tomography Dose Indices • Effective dose, E, provides risk estimate which depends on the body size and organs imaged as well as on the integral dose. • E is calculated as the product of DLP and conversion factors Shrimpton et al, BJR (2006) 79, 968-980 Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography

  50. Typical Doses in Paediatric CT *"Unadjusted" refers to using the same settings as for adults. "Adjusted" refers to settings adjusted for body weight. NCI: www.cancer.gov/cancertopics/causes/radiation-risks-pediatric-CT Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography