Download Radiation Dose in Pediatric Imaging

Radiation Dose in Pediatric Imaging
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?

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
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


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

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
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
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

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 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

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

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?

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
Exam
CXR (PA)
L-spine XR
Upper GI
VCUG
CT Head
CT Chest
CT Abdomen
Cardiac Cath
FDG-PET
Dose (mSv)
0.02
1.3
3
~0.33-2.5
~4
1-7
2-20
5-20
3-20
Dose (rem)
0.002
0.13
0.3
~0.033-0.25
~0.4
0.1-0.7
0.2-2
0.5-2
0.3-2
CXR equivalent
1
65
150
17-125
~200
50-350
100-1000
250-1000
150-1000
Adapted from Brody, et al. Radiation Risk to Children From Computed Tomography. Pediatrics Sept 2007
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;23:402–410

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
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
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

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 500 – 1 in 2000 risk.
 Or just call it 1 in 1000 and remember it

(Doesn’t really matter since world ending in December)

Ordering Physician
 No radiation comes from a scan that is not
performed

Performing Physician
 Technical means to reduce dose

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?
Ionizing
Radiation
Radiographs
Fluoroscopy
• UGI
• VCUG
CT, Nucs
Not So
Much
Ultrasound
MR
Waving
Sticks over
Patient
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


Resources for





Radiologists
Ordering physicians
Technologists
Parents
Educational materials
 Online
 Print
Protocols
 Links to reliable information

• Carcinogenesis
•Detection of lifethreatening
conditions
•Avoiding invasive
procedures
•Alter therapy
•…
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

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
Siemens FLASH CT
 Dual Source
 High table speed
 Fast as all hell


“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

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

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


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.

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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. National conference on
dose reduction in CT, with an emphasis on pediatric
patients. AJR Am J Roentgenol. 2003;181:321–329
Wiest PW, Locken JA, Heintz PH, Mettler FA Jr. CT
scanning: a major source of radiation exposure. Semin
Ultrasound CT MR. 2002;23:402–410
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: 823–832