1. Paediatric patient dose surveys Colin Martin and David Sutton

2. Overview Introduction Introduction 1. Chest and abdominal radiographs 1. Chest and abdominal radiographs 2. Dynamic procedures 2. Dynamic procedures

3. Why are kids special? higher risk than for adults higher risk than for adults often different techniques often different techniques less data available less data available only performed occasionally in some hospitals only performed occasionally in some hospitals lack of optimisation lack of optimisation

4. Radiation risk in children Greater chance for expression of radiation induced effects Greater chance for expression of radiation induced effects Greater sensitivity for some cancers Greater sensitivity for some cancers High frequency for some examinations High frequency for some examinations Lack of cooperation and optimisation Lack of cooperation and optimisation

5. Large numbers of images can be taken of new born babies K. Smans, Leuven

6. Sometimes over 100 images can be taken of new borns C. Maccia, Paris

7. Some Paediatric Exams Water soluble contrast studies Water soluble contrast studies Mict Cystogram for reflux Mict Cystogram for reflux Intussusception Intussusception Non-accidental injury assessment Non-accidental injury assessment Hips for displasia Hips for displasia

8. Fewer patients Paediatric exams only represent 1-2% of those in UK database (despite extra efforts to collect data) Paediatric exams only represent 1-2% of those in UK database (despite extra efforts to collect data) Only paediatric hospitals have sufficient patients for full survey Only paediatric hospitals have sufficient patients for full survey Other hospitals may have only a handful of patients even for commonest exams Other hospitals may have only a handful of patients even for commonest exams

9. X-ray equipment for paediatrics Generators Generators Filtration (additional copper) Filtration (additional copper) Paediatric anti-scatter grids Paediatric anti-scatter grids Automatic exposure control Automatic exposure control Low dose fluoroscopy Low dose fluoroscopy KAP meters with resolution of 0.1 mGy cm 2 KAP meters with resolution of 0.1 mGy cm 2 The Ideal is to use dedicated equipment. Factors to consider include:

10. 1. Paediatric Radiography Simple examinations Simple examinations Assess ESD or KAP Assess ESD or KAP Large range in patient size Large range in patient size

11. Best Practice Guidelines High speed screen/film systems High speed screen/film systems Avoid use of anti-scatter grids where possible Avoid use of anti-scatter grids where possible Additional filtration - copper Additional filtration - copper High kV-short exposure techniques High kV-short exposure techniques Gonad protection Gonad protection Dedicated equipment Dedicated equipment Trained staff Trained staff Cook et al, 1998

12. Use of Grids Use of an anti-scatter grid can double the dose Use of an anti-scatter grid can double the dose Children’s bodies are small Children’s bodies are small so there is less scattered radiation so there is less scattered radiation grids are often unnecessary grids are often unnecessary

13. New born child can be placed directly on cassette for radiograph

14. Influence of grid on dose Effect of introduction of grid for larger children

15. Poor collimation exposes sensitive organs unnecessarily

16. Good collimation for neonates Good collimation for neonates Achieved by positioning lead/rubber drapes on incubator Good radiation protection Poor radiation protection

17. Copper filtration: Removes low energy photons that are absorbed in superficial tissues Spectra of 80 kV X-ray beams with and without 0.2 mm copper Reduces skin dose Exposure adjusted to give similar dose at the image receptor X-ray photons removed Increase in mAs required Maintains good contrast

18. Dose quantities Radiography ESD : measured with TLD or calculated from tube output KAP : If KAP meter fitted Fluoroscopy KAP : measured with KAP meter

19. Dosimetry Problems low readings (KAP meters/TLD) give poor precision low readings (KAP meters/TLD) give poor precision TLD may be visible or cause practical difficulties TLD may be visible or cause practical difficulties calculations of dose complicated by variable patient size calculations of dose complicated by variable patient size small sample sizes small sample sizes uncertainties in effective dose and risk factors uncertainties in effective dose and risk factors

20. Exposure parameters & tube output measurements Need tube output (as a function of kV) from the medical physics report Need tube output (as a function of kV) from the medical physics report Need kV, distance and mAs values for exposure Need kV, distance and mAs values for exposureUncertainties: Accuracy of the distance data Accuracy of the distance data Field size Field size

21. Paediatric Data Collection Exam Exam Patient data essential Patient data essential –age –Height & weight  thickness Focus to Skin Distance Focus to Skin Distance Use of grid Use of grid Filtration Filtration

22. Why is size a problem ? Continuous size distribution (neonate to adult) Continuous size distribution (neonate to adult) Establishment of DRLs and comparisons with reference levels need to be meaningful Establishment of DRLs and comparisons with reference levels need to be meaningful Conflict arises between sample size and variability arising from patient size Conflict arises between sample size and variability arising from patient size

23. Increase in KAP with patient size Note that vertical axis is a log scale Courtesy T. Kiljunen, STUK, Finland

24. Possible Approaches Age banding Age banding Patients grouped together to provide sufficient data Patients grouped together to provide sufficient data Retrospective data analysis Retrospective data analysis Correction of data using effective attenuation coefficients Correction of data using effective attenuation coefficients

25. Size correction using effective attenuation coefficients Corrections can be made to data to enable patients with a range of ages/sizes to be used Equate to a patient of standard thickness ‘s’ F ESD = e µ(s-d) Where  = effective attenuation coefficient (derived from measurements of entrance and exit doses) with varying phantom thicknesses – fixed kV d = thickness of patient for which data collected Hart et al (2000): NRPB-R318 Hart et al (2000): NRPB-R318

26. Equivalent cylinder diameter Patient diameter can be equated to a standard cylinder of the same length and weight, if other data not available Patient diameter can be equated to a standard cylinder of the same length and weight, if other data not available Equivalent diameter = 2√[Weight/(  Height)] Density = ( 1 g cm 3 ) Equivalent diameter = 2√[Weight/(  Height)] Density = ( 1 g cm 3 ) h

27. Size correction for KAP Similar corrections can be made to KAP data F KAP = e µ(s-d) s 2 /d 2  = effective attenuation coefficient S = thickness of standard patient d = thickness of patient for which data collected Incorporates Incorporates FSD correction Field size correction for KAP Hart et al (2000): NRPB-R318

28. Age ranges 0 – 6 months  newborn 0 – 6 months  newborn 7 m – 23 m  1 y old infant 7 m – 23 m  1 y old infant 2 – 7 y  5 y old 2 – 7 y  5 y old 8 y – 12 y  10 y old 8 y – 12 y  10 y old

29. National patient dose survey Collect data from hospitals Collect data from hospitals Input data into database Input data into database Calculate mean KAP or ESD Calculate mean KAP or ESD Compare data from all centres Compare data from all centres

30. National Survey Distribution of doses for paediatric chest Identify the 3 rd quartile dose for use as DRL 75% below DRL; 25% above need optimisation 3 rd Quartile - 70 mGy

31. Setting DRL based on ESD data for agreed age band DRL 70 mGy Third Quartile

32. UK Paediatric Radiographic DRLs Exam Age (y) European 1996 ESD (mGy) UK 2000 ESD (mGy) Chest AP/PA 0-10.080.05 50.100.07 100.12 Pelvis AP 10.20.5 50.90.6 100.7 152.0 Abdomen AP 10.4 51.00.5 100.8 151.2

33. Regional patient dose survey Compare data from all centres Compare data from all centres For non-paediatric hospitals it may be necessary just to collect standard factor data for some examinations For non-paediatric hospitals it may be necessary just to collect standard factor data for some examinations Investigate possible reasons for high doses above DRL Investigate possible reasons for high doses above DRL Produce individual report for each centre Produce individual report for each centre Liaison with individual hospitals is necessary to ensure optimisation of protection Liaison with individual hospitals is necessary to ensure optimisation of protection

34. Issues with survey data … Include patient weight Include patient weight 20+ patients if possible 20+ patients if possible Reset KAP meter after each examination Reset KAP meter after each examination Quote KAP in correct units Quote KAP in correct units Often large differences between centres Often large differences between centres

35. Neonatal dose data from factors used in District General Hospitals Hospitals rarely carry out examinations and factors are not optimised Hospitals rarely carry out examinations and factors are not optimised National DRL

36. Patient dose survey report

37. Reasons for high DAP values - Radiographic Low patient numbers Low patient numbers Patient weight not given Patient weight not given Using a low kV Using a low kV KAP quoted in wrong units KAP quoted in wrong units KAP meter not reset after each patient/examination KAP meter not reset after each patient/examination Different techniques used Different techniques used

38. 2. Dynamic examinations Less frequent Less frequent KAP measurements KAP measurements Effect of the weight? Effect of the weight? More complicated to calculate effective doses More complicated to calculate effective doses

39. UK Paediatric Fluoro DRLs Exam Age (y) KAP (cGy cm2) Barium Meal 010 1, 5 20 1070 1200 Barium Swallow 020 140 550 10180 MCU010 1, 5 30 1040 1590

40. DAP v age for MCU BJR 72:763-772 (1999) Courtesy of F. Schultz

41. Reasons for high DAP values Patient weight not given Patient weight not given Low patient numbers Low patient numbers High pulse rate High pulse rate Old equipment Old equipment Large variation in screening times Large variation in screening times Protocols not being followed Protocols not being followed

42. Summary Paediatric dosimetry is not straightforward Paediatric dosimetry is not straightforward Dose measurement/calculation methodologies need to be well thought out Dose measurement/calculation methodologies need to be well thought out A consistent approach to patient size correction is needed A consistent approach to patient size correction is needed Dose quantities need to be appropriate for task Dose quantities need to be appropriate for task

43. Any Questions?