Radiation Dose in Pediatric Imaging

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Andra Lamb
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1 Radiation Dose in Pediatric Imaging

2 A Brief History of Radiology Dose: Why Does It Matter? Measuring Exposure and Dose Deterministic Effects Stochastic Effects Common Exams: What is the Risk? Reducing Radiation Exposure What Do I Tell Parents?

3 November 8, 1895 Wurzburg, Germany Wilhelm Conrad Roentgen Working with vacuum tubes Caused fluorescence Shadows cast by different materials First subject: his wife Duly impressed

5 By 1896, adverse effects being reported 1904: Death of Edison s assistant, Clarence Dally Many early pioneers begin to be affected First early attempts at protection

6 Measuring exposure and dose How do we quantify it? Biological Effects of Radiation Deterministic Stochastic Estimate risk Analyze known exposure data Extrapolate to general population

7 Exposure: Measurement of ionizations produced in air Dose: Amount of energy imparted to a material SI: Gray (Gy) Conventional: rad Equivalent Dose: Ionizing material deposited into tissue Implies/accounts for biologic activity SI: Sievert (Sv) Conventional: rem

8 1 Gy 1 Sv Conventional 100 rad 1 rad 100 rem 1 rem 1 rad 1 rem SI 1 Gy 0.01 Gy, 10 mgy 1 Sv 0.01 Sv, 10 msv

11 Atomic bomb survivors Radium dial painters, uranium miners Secret Program Involving Radioactive Snacks at Primary Care Conference Much uncertainty surrounds projection of radiation risks from this limited data

12 Occur at a relatively high threshold dose Beyond that of diagnostic imaging Erythema ~5 Sv (500 rem) Cataract formation Acute at ~2 Sv (200 rem) Sterility Temporary at ~150 msv (15 rem)

The Big One: Radiation Carcinogenesis Occur with low radiation doses Linear-No Threshold Model No threshold dose Dose proportionally affects the probability of a randomly occurring event Risk

13 The Big One: Radiation Carcinogenesis Occur with low radiation doses Linear-No Threshold Model No threshold dose Dose proportionally affects the probability of a randomly occurring event Risk increases linearly with dose Generally accepted but unproven model Affected by other factors Long latent period before effect Age at exposure Gender Leukemia: 5-10 years Solid tumors: decades

14 Data skewed toward brief, high-dose exposure Atomic survivors <3km from blast received doses above background Those <2km fatally burned Data superimposed upon natural cancer occurrence rates Vary for populations Approximately 20% No marker for radiogenic cancers

15 Risks are calculated, not observed Prospective studies would be staggeringly difficult to perform Natural sources of radiation Vary by geography Models don t seem to fit this perfectly Radiation hormesis? Is there a dose that is not only safe, but beneficial?

16 Cosmic rays, terrestrial, internal sources 1.2 msv/year (0.12 rem) Another 1.2 msv/yr from radon ~0.5 msv/yr from medical and consumer product sources ~3 msv/yr average Variable Results in 1% lifetime risk of fatal cancer

17 Exam CXR (PA) L-spine XR Upper GI VCUG CT Head CT Chest CT Abdomen Cardiac Cath FDG-PET Dose (msv) ~ ~ Dose (rem) ~ ~ CXR equivalent ~ Adapted from Brody, et al. Radiation Risk to Children From Computed Tomography. Pediatrics Sept 2007

18 Procedures Radiation Involving Exposure Ionizing Radiation Other 25% Other 85% CT 15% CT 75% Wiest et al. CT scanning: a major source of radiation exposure. Semin Ultrasound CT MR. 2002;23:

19 CT utilization is constantly growing ~10% per year increase Why? It s good. Detects treatable cancers, other conditions of considerable morbidity/mortality Obviates unnecessary invasive procedures Accessible, fast, accurate New innovations increase its utility ~10% of CT exams are of children 7+ million pediatric CT exams per year

20 Longer life expectancy Greater sensitivity of developing organs More time for latent effects of exposure Smaller body mass Receive greater dose than an adult for the same exposure Greater Risk

21 Nobody really knows for sure Best estimate: Risk of fatal cancer: 5%/Sv CT Abdomen: 2-20 msv For 1000 patients scanned at 20 msv: 1 expected to die prematurely 0.1% risk 99.9% chance of no radiation induced cancer

22 But you said kids are more susceptible to radiation effects! OK, then: 1 in 500 risk But you said that we care about the children and reduce dose! OK, then: 1 in 2000 risk But you said you would make this simple! OK, then: 1 in in 2000 risk. Or just call it 1 in 1000 and remember it (Doesn t really matter since world ending in December)

23 Ordering Physician No radiation comes from a scan that is not performed Performing Physician Technical means to reduce dose

24 How indicated is an imaging study? Is there a role for imaging? What effect will it have on management? Which study to order? Can the question be answered without ionizing radiation? How can it be answered with the least exposure to the patient? What are the benefits vs. the risks?

25 Ionizing Radiation Radiographs Fluoroscopy UGI VCUG CT, Nucs Not So Much Ultrasound MR Waving Sticks over Patient

26 Evidence-based, expert panel, and consensus recommendations Rate imaging studies based on appropriateness for common clinical issues Rate studies on relative radiation dose to the patient Very useful tool to guide ordering physicians and radiologists in workup

30 Resources for Radiologists Ordering physicians Technologists Parents Educational materials Online Print Protocols Links to reliable information

31 Carcinogenesis Detection of lifethreatening conditions Avoiding invasive procedures Alter therapy

32 The ALARA Principle Is there a better way to answer the clinical question? It s not that I m lazy: it s because I care about the children And also, I am lazy Consult your radiologist if you have a question Between the hours of 8 and 5

33 Limit scan coverage Only to areas of concern Decreasing phases of imaging Multiphase CT uncommonly necessary Decreasing Technique Factors Decreasing kvp: exponential reduction Decreasing mas: linear reduction Weight-based protocols Determine level of detail needed

34 Siemens FLASH CT Dual Source High table speed Fast as all hell

35 X-care Adaptive Dose Shield Tube off for a portion of rotation Decreases dose to sensitive organs Collimates spiral beam at beginning and end of scan Reduces overscan Iterative Reconstruction (IRIS) Math stuff Longer reconstruction time 30% dose reduction

36 Healthcare Professionals Surveys have shown poor awareness Relative amounts of dose Potential for increase in lifetime cancer risk Parents Level of awareness (or interest) Sources of information Lay press Teh Interwebz

38 Risks from Diagnostic Imaging are very low Safe is probably not the best term to use Risks do exist, though they are estimated Primarily relate to development of cancer Risk increases with increasing dose On the order of 1 in 1000 for CT This is the best information we have Steps are taken to reduce dose

39 This CT is just as safe as standing a mile away from Hiroshima on August 6, 1945 Chances are actually very small that your child will disintegrate, be endowed with superhuman powers of eeevil, or otherwise become a social delinquent. At least because of this study Genetics play a role, you know Please ask to chat with our radiologists. They are friendly, knowledegable, and Risk Management absolutely loves it when they talk to patients.

Brody AS, Frush DP, et al. Radiation risk to children from computed tomography. Pediatrics. 2007;120:3;677-82 Linton OW, Mettler FA Jr. National Council on Radiation Protection and Measurements.

41 Brody AS, Frush DP, et al. Radiation risk to children from computed tomography. Pediatrics. 2007;120:3; Linton OW, Mettler FA Jr. National Council on Radiation Protection and Measurements. National conference on dose reduction in CT, with an emphasis on pediatric patients. AJR Am J Roentgenol. 2003;181: Wiest PW, Locken JA, Heintz PH, Mettler FA Jr. CT scanning: a major source of radiation exposure. Semin Ultrasound CT MR. 2002;23: Brody AS, Guillerman RP. Radiation risk from diagnostic imaging. Pediatric Annals. 2002;31:10 Thomas KE, Parnell-Parmley JE. Assessment of radiation dose awareness among pediatricians. Pediatr Radiol (2006) 36:

Debra Pennington, MD Director of Imaging Dell Children s Medical Center

Debra Pennington, MD Director of Imaging Dell Children s Medical Center 1 Gray (Gy) is 1 J of radiation energy/ 1 kg matter (physical quantity absorbed dose) Diagnostic imaging doses in mgy (.001 Gy)