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IAEA International Atomic Energy Agency Radiation Protection in Paediatric Radiology Radiation Protection of Children During Computed Tomography L06.

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Presentation on theme: "IAEA International Atomic Energy Agency Radiation Protection in Paediatric Radiology Radiation Protection of Children During Computed Tomography L06."— Presentation transcript:

1 IAEA International Atomic Energy Agency Radiation Protection in Paediatric Radiology Radiation Protection of Children During Computed Tomography L06

2 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 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.

3 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 3 Answer True or False 1. Reduction of kVp in CT reduces the dose. 2. CT contributes % of the dose from radiological examinations in developed countries. 3. The same CT protocol used for children and adults will result in a higher dose to adults.

4 IAEA 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.

5 IAEA 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.

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

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

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

9 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 9 Single Detector (SDCT) vs Multi-detector (MDCT) Computed Tomography M. Mahesh, MDCT physics, the basic technology, image quality and radiation dose, Wolters Kluwer, 2009 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

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

11 IAEA 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.

12 IAEA 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 Approximately 10% growth rate per year 7 million CT examinations per year in children % increase in paediatric CT from 2005/06. Up to 31% of paediatric body CT examinations are multiphase in some reports

13 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 13 Facts About CT… 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 METTLER, F.A., et al., J. Radiol. Prot (2000)

14 IAEA 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

15 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 15 Amount of Radiation Resulting From CT ExaminationEffective Dose (mSv)Chest X-ray Equivalents 3-view ankle radiography view chest radiography0.021 Radionuclide cystogram0.189 Flouroscopic cystogram~0.33~16 Radionuclide bone scan~5~250 Brain CT2100 Chest CTup to 3up to 150 Abdominal CTup to 5up to 250 Frush D, et al, CT and Radiation Safety: Content for Community Radiologists

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

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

18 IAEA 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: : 2000.

19 IAEA 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

20 IAEA 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

21 IAEA 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

22 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 22 In Paediatric Radiology… It estimated that between a third and half of 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)

23 IAEA 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…

24 IAEA 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.

25 IAEA 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

26 IAEA 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

27 IAEA 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.

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

29 IAEA 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.

30 IAEA 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

31 IAEA 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.

32 IAEA 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.

33 IAEA 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

34 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 34 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 Equipment, Protocol, Dose and Image Quality

35 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 35 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 Equipment, Protocol, Dose and Image Quality Nievelstein, Pediatr Radiol, 2010

36 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 36 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.… Equipment, Protocol, Dose and Image Quality

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

38 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 38 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. Equipment, Protocol, Dose and Image Quality

39 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 39 Equipment, Protocol, Dose and Image Quality 1. 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)

40 IAEA 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 be achieved tube current (mA) can be automatically adjusted to keep the dose and noise the same

41 IAEA 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.

42 IAEA 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: Use of tube current modulation technology results in dose reduction by 60% for paediatric scanning, Kalra et al, 2004, Radiology, 233:649-57

43 IAEA 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.

44 IAEA 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

45 IAEA 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

46 IAEA 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 (CTDI vol ) and Dose-length product (DLP) on the console (Requirement from IEC ). 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.

47 IAEA 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 (CTDI vol ) Dose Length Product (DLP)

48 IAEA 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

49 IAEA 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,

50 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 50 Typical Doses in Paediatric CT Exam typeRelevant organ Range of absorbed organ doses (mGy) Range of effective doses (mSv) Head unadjusted* (200 mAs) Brain Head adjusted (100 mAs) Brain Abdomen unadjusted (200 mAs) Stomach Abdomen adjusted (50 mAs) Stomach NCI: *"Unadjusted" refers to using the same settings as for adults. "Adjusted" refers to settings adjusted for body weight.

51 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 51 Equipment, Protocol, Dose and Image Quality 9. Viewing Conditions: Make sure windows levels and settings are adequate and that the monitors are calibrated.

52 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 52 Equipment, Protocol, Dose and Image Quality 10. Shielding: Lead shielding can be place over the male gonads if: the edge of the volume of investigation is less than cm away it does not interfere with the image Dauer, et al, BMC Medical Imaging 2007, 7:5 doi: /

53 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 53 Equipment, Protocol, Dose and Image Quality The use of reusable bismuth attenuation shields is possible for sensitive organs such as the eyes, gonads, breasts and thyroid. 10. Shielding:

54 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 54 Shielding The bismuth eye shield is simple to place and covers only the eye In-plane shields are associated with greater image noise and streak artifacts. However, shields reduce radiation dose. Automatic exposure control did not increase radiation dose when using a shield. Karla et al, Korean J Radiol. 10:156-63, 2009 This adult patient has a 3 layer bismuth latex eye shield in place. While artefact is seen into the globe, no artefact is transmitted into the brain. Standoff pads can reduce surface artefact Hopper KD, et al, Am J Neuroradiol 22:1194–1198,2001

55 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 55 Equipment, Protocol, Dose and Image Quality 11. Training The examination should always be supervised by a radiologist experienced in paediatric imaging If all listed factors are taken into consideration, significant dose reduction can be achieved

56 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 56 Training Following options are available on modern scanners Tube current modulation (mA, mA/slice, effective mAs), pitch, noise level setting, field-of-view for bow tie filter, kVp, beam (vs slice) collimation… This requires a skilled operator: Who knows well the model of the scanner using Trained in paediatric imaging to adjust the examination parameters according to examination type, age and/or size of the child

57 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 57 Radiologists, Physicists and Technologists’ Responsibilities Improve awareness of need to decrease CT radiation dose to children. Be committed to make a change in daily practice by team work between radiologists, technologists, referring healthcare providers and parents. Medical physicists, radiologists, technologists and department managers should review vendor or other CT protocols and “down-size” them for children.

58 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 58 Radiologists, Physicists and Technologists’ Responsibilities Single phase scans are often adequate Pre- and post-contrast or delayed scans rarely add additional information in children, but can double or triple the dose.

59 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 59 Radiologists, Physicists and Technologists’ Advice Scan only the indicated area. If a patient has a possible small dermoid on ultrasound, there may not be a need to scan the entire abdomen and pelvis. Be involved with your patients. Be the patient’s advocate. Ask the questions required to ensure that you “child-size” the scan.

60 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 60

61 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 61

62 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 62 Summary CT can be a relatively high dose diagnostic imaging procedure Rigorous justification of CT for children is required Good practice in paediatric CT: Optimisation of the CT examination protocol based on patient size (lower kVp and mA) Acceptance of images with greater noise One scan (single phase) is often enough - Reduce repeat scanning of identical body areas Scan only the indicated area Use of shielding devices Trained and experiences staff

63 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 63 Answer True or False 1. Reduction of kVp in CT reduces the dose. 2. CT contributes % of the dose from radiological examinations in developed countries. 3.The same CT protocol used for children and adults will result in a higher dose to adults.

64 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 64 Answer True or False 1. Тrue - Reduced kVp reduce the dose in children while maintaining image quality. 2. Тrue - It is a high dose modality and with 10% contribution to number of all radiological examination it gives 60-70% of dose. 3. False- It is opposite, the same protocol will give a few time higher dose to children.

65 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 65 References BRENNER, D.J., ELLISTON, C.D., HALL, E.J., BERDON, W.E., Estimated risks of radiation-induced fatal cancer from paediatric CT, Am. J. Roentgenol. 176 (2001) BRENNER, D.J., Estimating cancer risks from paediatric CT: going from the qualitative to the quantitative, Pediatr. Radio.l 32 (2002) 228 – 231. FRICKE, B.L., et.al., In-plane bismuth breast shields for pediatric CT: effects on radiation dose and image quality using experimental and clinical data, Am. J. Roentgenol. 180 (2003) 407 – 411. HOPPER, K.D.,et al, The breast: in-plane x-ray protection during diagnostic thoracic CT - shielding with bismuth radioprotective garments, Radiology 205 (1997) 853 – 858. KILJUNEN, T., JÄRVINEN, H., SAVOLAINEN, S., Diagnostic reference levels for thorax X-ray examinations of paediatric patients, Br. J. Radiol. 80 (2007) BOONE, J.M., et. al., Dose reduction in paediatric CT: a rational approach, Radiology 228 (2003) LUCAYA, J., et. al., Low-dose high-resolution CT of the chest in children and young adults: dose, cooperation, artefact incidence and image quality, Am. J. Roentgenol. 175 (2000) INTERNATIONAL ATOMIC ENERGY AGENCY, Dose Reduction in CT while Maintaining Diagnostic Confidence: A Feasibility/Demonstration Study, IAEA-TECDOC-1621, IAEA, Vienna, (2009). KALRA, M.K., et. al., Techniques and applications of automatic tube current modulation for CT, Radiology 233 (2004) INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, ICRP Publication 102: Managing Patient Dose in Multi-Detector Computed Tomography (MDCT), Annals of the ICRP Volume 37/1, Elsevier, (2007). D. Tack,Pierre A Gevenois, Radiation Dose from Adult and Pediatric Multidetector Computed Tomography, Springer, 2007 Karla et al, In-plane shielding for CT: effect of off-centering, automatic exposure control and shield-to- surface distance, Korean J Radiol Mar-Apr;10(2):

66 IAEA Additional material

67 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 67 Practical Optimisation in Paediatric CT (I) Reduce mAs according to body weight/diameter or composition and/or Use dose modulation (angular/longitudinal) Use maximal slice reconstruction thickness to reduce noise and potentially dose appropriate for specific diagnosis. Decrease kVp for thin (small) patients and high contrast exams (CT angiography, chest, musculoskeletal )

68 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 68 Practical Optimisation in Paediatric CT (II) Normally use shortest rotation time available. Use representative volume sample when entire volume is not needed. Use spiral scan with pitch greater than 1 (eg.: 1.5), provided this does not automatically increase the mA. Use newer dose reduction strategies such as iterative reconstruction and adaptive modulation (to reduce over ranging)

69 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 69 Practical Optimisation in Paediatric CT (III) Be restrictive in defining upper-most and lower- most scan range Use localising projection scan extending just minimally beyond scan limits. Consider low kVp and single AP topogram Reconstruct additional thick noise-reduced slices without increase in exposure. Avoid major overlap when scanning adjacent areas with different protocols

70 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 70 Practical Optimisation in Paediatric CT(IV) Avoid additional non-enhanced scans unless specifically justified. Optimise the protocol to obtain all the information requested during one scan. Minimise the number of scans in multi-phase scanning. In case of multi-phase scanning use shorter scan length for additional scans. Use lower dose for non-enhanced or repeat scans unless high quality is needed.

71 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 71 Practical Optimisation in Paediatric CT (V) Minimise length of scans and fluoroscopy time in interventional applications. Use low mA with CT fluoroscopy Replace test bolus/bolus triggering by standard can delay unless timing is very critical. Use additional protection devices where indicated such as bismuth shields (lens, thyroid, breast, gonads).

72 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 72 Tube current modulation: Based on patient's size Longitudinal (z-axis) Angular (xy-axis) Combined Thick patientThin patient Tube Current Modulation Options

73 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 73 Tube Current Modulation Options Dose reduction based on patient anatomy. Lower mA in AP, higher mA in lateral directions. 1 GE, 2 Toshiba and 3 Siemens MDCT 200 mA 150 mA 130 mA 150 mA 180 mA 210 mA 200 mA 170 mA 180 mA Methods Patient attenuation measured during scout scan (AP & Lat) and alter mA for each gantry rotation (Smart mA 1, Real AEC 2 ) or “ on-the-fly ” (Care dose 3 )

74 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 74 Tube potential (kVp) Decreasing kVp significantly reduces dose, typically: 80 kV – 0.5 mSv 100 kV – 1 mSv 120 kV – 1.6 mSv 140 kV – 2.3 mSv kV = dose

75 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 75 Tube potential (kVp) CT examinations with a high intrinsic contrast (chest, bones) justify lowering the tube voltage to 80–100 kVp However, bony examinations can be performed with very low current 25-70mA Nievelstein, Pediatr Radiol, 2010 Cook, Imaging, 2001

76 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 76 Guidelines FDA Public Health Notification: Reducing Radiation Risk from Computed Tomography for Paediatric and Small Adult Patients, November 2nd, 2001 National Cancer Institute: Radiation Risks and Paediatric Computed Tomography (CT): A Guide for Health Care Providers, pediatric-CT pediatric-CT Image Gently:

77 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 77 A Practice Quality Improvement (PQI) Program in CT Scans in Children: The PQI module capture how your practice performs CT scans in children, and allows you to compare your practice to “safe practice” guidelines in the literature. How to Develop CT Protocols for Children? Provide guidance in developing CT protocols for children and periodically verifying that your current protocols are appropriate

78 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 78 Example of successful story I Arch and Frush, AJR 2008;191:611–617: Since 2001, kVp and mA settings, two principal parameters determining radiation dose, have decreased significantly for paediatric body MDCT It is a reasonable assumption that these changes are due to efforts to increase awareness about the risks of radiation Paediatric chest CT

79 IAEA Radiation Protection in Paediatric Radiology L06. Radiation protection in computed tomography 79 Example of successful story II Wallace, et al. Proceedings of IRPA 12, Buenos Aires, 2008, FP0227: Eight paediatric hospitals Training and seminars on optimisation Dose reduction greater than 50%


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