Transcript Assessing Risk from Medical Radiation

Elizabeth H. Ey, M.D.
Medical Director Radiology
Dayton Children’s Medical Center
Content of presentation and pictures
courtesy of
Thomas Slovis, M.D.
and
The Society for Pediatric Radiology
Survey
Has anyone here read a news report of
radiation exposure from medical imaging?
Survey
Has anyone had a patient or family member
ask them about radiation exposure
from medical imaging?
Survey
Has anyone had a test question in medical education
(or CME) regarding radiation exposure to patients
from medical imaging tests?
Questions
 What is our natural background level of radiation?
 What is the radiation dose of a 1 view chest
radiograph?
 What is the radiation dose of a 1 view abdomen
radiograph?
 What is the radiation dose of a CT scan?
 Head CT dose?
 Abdomen CT dose?
Answers
 Natural occurring background radiation
 Chest, one view, child, skin dose
 Abdomen, one view, child, skin dose
 CT Head, child, minimal dose, CTDI
 CT Abd, child, CTDI
1 mrad/day
3-15 mrad
50 mrad
2000 mrad
>1000 mrad
What is the increased risk of death
from cancer from 1 CT scan
performed in a child?
A
B
C
The increased risk of cancer death from a CT
scan is 0.
The increased risk of cancer death is between 1
in 1000 to 1 in 5000 over a lifetime.
The increased risk of cancer death is 1 in 1
million over a lifetime.
Answer
 B It is estimated that an abdominal CT
scan results in 1/1000 to 1/5000 excess
risk of cancer at a later date.
What is the current lifetime risk of
developing cancer (US)?
dying of cancer (US)?
Lifetime risk of cancer (US)
Developing Dying
Male
Female
44.05%
37.6%
23.24%
19.65%
N Engl J Med 2007: 357:2277-84
USA Today Nov 29, 2007
USA Today
Nov 29, 2007
Medical Radiation in Medicine
 When indicated it can diagnose illness
 Noninvasive, painless, fast, extremely accurate
 But like any medication or therapy
 Too much radiation can lead to deleterious effects

DETERMINISTIC effect –linear, direct, ex: skin reddening
 Any radiation dose can cause lethal effect – cancer

STOCHASTIC effect – non-linear, random, takes time to see
Think of radiation as a medicine
 Effects are lifelong and cumulative
 Particularly severe effect in infants and children
 Especially when adult doses are used in children
 Age dependent – younger patient more severely effected
 No dose of radiation can be considered completely
safe
 Linear non-threshold effect
Oath of Hippocrates
“Above all, do no harm.”
ALARA Concept for
Pediatric Radiation Dose
As
Low
As
Reasonably
Achievable

Medical Radiation in Children
1. History of Radiology
2. Basic dosimetry
3. Biology of radiation effects
4. Unique issues with radiation in children
5. Use of appropriate techniques
6. Joint efforts with healthcare providers
History
 Dec 28, 1895: Roentgen submits manuscript describing his
discovery of “x-ray” to the Physical Medical Society of
Wurzburg: manuscript printed and distributed in 3 days
 Jan 9, 1896: manuscript appears in Vienna Press
 Jan 23, 1896: manuscript appears in Nature, in England
 Jan 23, 1896: Roentgen presented paper to Physical
Medical Society of Wurzburg
 By mid 1896, fluoroscopy was in widespread practice
 From clinical bench to widespread use in 6 months
Wurzburg Medical-Physics Society 1896
Dr. Kohler, famous anatomist, having hand X-rayed
by Roentgen at the meeting.
Level of Radiation Safety Circa 1896
First Pediatric Radiograph
14 minute exposure
Roentgen received the first Nobel
Prize in 1901 for his discovery
Application of Radiation Sciences
for Medical Diagnosis:
Tremendous benefits
Risks became evident with
increasing use
Side Effects of Radiation in Humans
Started being reported within
months of discovery of x-ray
Public Spectacle: Side Effects
 Deep sunburn
 Hair loss
 Bloodshot eyes, vision impaired
 Transient effects
Transient Hair Loss
40 min fluoro 18 inches from head
Practitioners in X-ray techniques
were the first to show the
long term effects of
radiation exposure
Radiologist with Skin Carcinoma
Monument to Martyrs in X-ray and
Radium Physics – 1936 Hamburg
 Albers Schonberg
 Madame Curie
 Caldwell
 Codman
Br J Radiol 2001; 74: 507- 519
Berrington A, Darby SC, Weiss HA, Doll R
 Research on 100 years of data on health
of radiologists in Great Britain
 1897-1954 – 41% excess of cancer deaths
in practitioners of radiology
 1954-1997 – zero excess mortality from
cancer in the practitioners of radiology
Learned biologic effects of radiation
 Applied what we learned to protect ourselves
 It worked
 But have we done enough?
 Have we protected our patients enough?
2. Basic dosimetry
• Dose units
• Measures of dose
• Conversions
Radiation Dose Units
Methods of Measuring Radiation Dose
 Widely varied and difficult to compare
 Entrance skin dose
 Exit dose
 Dose area product (DAP)
 Organ dose –specific to radiosensitive organ
 Radiation output measured within a phantom
 CT dose index (CTDI)
 Dose equivalent
 Effective dose
Radiation Dose Measurements
Used for Risk Assessment
 Absorbed Dose – Gray or Gy (previous rad)
 Risk assessment for a specific organ or tissue
 Difficult to measure and not very useful
 Effective dose equivalent – Sievert or Sv (previous rem)
 Non-uniform exposure to organ or region
 Expression of risk equivalent to whole body exposure
 CT scanner dose units not useful
 CTDI vol and DLP determined by phantom
 Not helpful for assigning risk without conversion
CTDI – CT Dose Index
 Reported on scanner consoles
 Based on phantom (16 or 32 cm diameter)
 Only represents the dose to the phantom based
on CT parameters selected
 Does not indicate dose to the child in the CT
scanner
 Conversions of CTDI to effective dose are only
rough estimations for children
 e.g. no age based chest modifications
Dose Chart
 1 Gy = 100 rads = 1 Sv
 10 mGy = 1 rad = 10 mSv
 0.01 mGy = 1 mrad = 0.01 mSv
Effective Dose
 It is a radiation dose quantity
 It is a computation based on:
Organ dose and radiosensitivity
Weighting factors
 It is not a risk number
Huda, W Pediatric Radiology 2002: 32; 272-279
3. Biology of radiation effects
Types of Biological Effects
from Radiation
 Deterministic effects
 Stochastic effects
Deterministic Effect
• Seen with high radiation dose
• Severity of effect is dose dependent:
• There is a threshold below which dose
the effect is NOT seen.
• Examples: skin burns, hair loss
Deterministic Effects
AJR July 2001 - Skin burns from
cardiac interventional procedures
Stochastic Effect
Low dose, random effect
Non dose dependent:
•Risk of the effect is dose dependent but
the severity of the effect is not.
•Example: Risk of cancer increases
with increasing dose but the severity
of the type of cancer is not dose
dependent
•There is “no threshold” to this effect
Stochastic Effect
 Means all or none (random effect)
 Not based on a particular dose
 But with higher radiation absorbed dose,
the higher the likelihood of genetic damage
 Mostly concerned with risk of carcinogenesis
 Incidence – twice the mortality risk
 Mortality - risks that are quoted here
Biological effects of radiation
damage to DNA
•Reactions are rapid
•Induction of cancer takes many years
•The damage to DNA may lead to genomic
instability
Genomic Instability
“Persistent enhancement in the rate of
which genetic change arises in the
descendents …..”
Little
Stochastic Effect (Random) on Irradiated Stem Cells
 C. and D. are the
effects seen in reality
 The irradiated cell
transmits the genetic
defect randomly into
future cell generations
 Cancer may not be
seen for several cell
generations
Little JB: Ionizing Radiation in Cancer in Medicine 2003
4. Unique issues with
radiation exposure to children
 Children are smaller and have more radiation
sensitive tissue
 Have a longer life expectancy in which to express
the damaging effect of radiation
 Is there a threshold for low dose radiation in which
no effect will be seen? Debated
Breast Cancer and Scoliosis Films
Doody et al. Spine 25:2052- 2063 year 2000
Thyroid Cancer after
Childhood Radiotherapy
Ron, E Pediatric Radiology 2002 32: 232- 237
Infant Radiotherapy for
“Enlarged Thymus”
… 96 minutes of x rays
Fetal Exposure
Oxford Study of Childhood Cancer
Obituary in New York Times 2002
Cancer risk in fetuses exposed in 3rd trimester
The excessive risk is 47% in the fetuses irradiated.
Atomic Bomb Survivor Follow Up
Pierce and Preston 2000
 Original 84,000 survivors followed for 55
years
 Eventually had 50,000 survivors that
were followed (1988-1994)
 Increased cancer rate even at low dose
(0.05-0.15 Sv or 500 mrad-1.5 rad)
 Excessive cancer deaths were
demonstrated
Pierce et al; Rad Res 154 pg 183: 2000
.... = cancer death rate for at-risk population (A bomb survivors)
__ = cancer death rate otherwise expected
Straight lines represent two different starting points to guess at which point
radiation dose is a problem. One begins at zero and the other at 0.06 Sv.
Is there a safe dose?
 Linear non-threshold (NLT) dose
 Dose below which there is no risk of
carcinogenesis?
NCRP Report – cannot prove safety
of any radiation dose
Linear No-threshold Principle
 “There is no need to even consider a linear
no-threshold principle when we have direct
human evidence of carcinogenesis at
doses of <10mSv.”
 Pierce DA, Preston DL 2000; 154:178-186
Linear No-threshold Principle
 LNT is NOT the issue!
 “Other populations” have not had 50 years
of meticulous research to detect cancer
 Sample size – 84,000 people at start of
study
 Age at exposure was known from the start
 Length of follow-up – over 55 years of f/u
AJR Feb 2001
Brenner et al AJR Feb 2001
Typical Radiation Doses (mSv)
• Average annual technologist dose
3.2
• Natural annual background
3.5
0.09
8.75
• Dental x-rays
 BE (marrow)
• CXR (marrow)
• Mammogram (breast)
• Airline passenger
• Flight crew / attendants annual
• CT
0.01
0.5 - 7.0
0.03
1.6
< 1.0 – 30 mSv
CT radiation doses can overlap
radiation exposure doses calculated
for survivors of the A-bomb.
Pierce, Preston; Rad Res, 2000; 151 pg 178-186
Brenner; Pediatric Radiology, Apr 2002; pg 230
Brenner et al 2003
“Above doses of 50-100 mSv (protracted
exposure) or 10-50 mSv (acute exposure), direct
epidemiologic evidence from human populations
demonstrate the exposure to ionizing radiation
increases the risk of some cancer.”
www.pnas.org/cgi/doi/10.1073/pnas.2235592100
AJR Feb 2001
CT Use in the US
 Increased dramatically in the recent years
 Estimated that 11% of all CT scans
performed in the US are performed in
children
 There is a risk of cancer death from CT
radiation dose
 The younger the patient, the greater the
risk
N Engl J Med Nov 2007
Brenner and Hall
Infants are 10-15 times more
vulnerable than middle age adults
Brenner et al; Pediatric Radiology, Apr 2002: pg 230
Females are at higher risk.
Age at exposure is the most important factor.
Hall Pediatric Radiology Apr 2002 pg 226
Important Concepts
 Greatest effect is on actively growing cells
 Infant, fetus
 Cumulative dose, life long effect
 EDE – Effective Dose Equivalent
 For the same dose, a child is much more
vulnerable because of the way the dose is
calculated.
 When measuring the dose at the midpoint of an
adult phantom (32 cm), the beam has already
passed completely through the child.
Consider the Premature Infant
 Hepatoblastoma
 Occurs at a higher rate in premature infants (40%)
 Infants studied by Alicia Stewart were term
infants
 Our premature infants can now survive at
23-24 weeks gestation
 The premature infant is at much higher risk
to radiation exposure.
5. Use of Appropriate Technique
 Film screen radiography - using more
radiation exposure than needed results in
a black image
 Digital and computed radiography with
post-processing – can make almost any
overexposed image look diagnostic by
manipulating contrast and brightness
Shunt Survey
Can’t tell
technique just
by looking at it
Dose parameters should be
included whenever possible
Uncoupling end result from
information regarding dose
is a dangerous practice
 When the exam does not include the technique
parameters used to acquire the images,
 The amount of radiation used may be more than
needed.
Assessing Risk
CT related cancer death
1000-5000/million in a life
time (not per year)
Radiation dose 100-600
times less than CT dose
6. Joint Efforts of Health Care Workers
What can be done?
What resources are available?
We are all responsible
 Practitioner who orders CT
 Radiologist who determines CT protocol
 CT technologist that performs the CT scan
How do we respond?
 Be sure that an imaging test is necessary
 Use the least invasive modality which gives
a high likelihood of correct diagnosis
 Consider all the options for imaging

MR and US use NO radiation
 Discuss the case with a pediatric radiologist
if uncertain which modality to use
When CT is used appropriately
 It saves lives
 Fast, accurate, comprehensive
 Especially useful for trauma patients or emergency conditions
 It has the greatest detail in imaging
 Sub mm resolution (IAC), high resolution lung detail
 It is less sensitive to patient motion than MR
 It is less sensitive to gas than US
 It creates a volume of data which permits multiplanar
reconstruction as well as 3D surface rendering
How do we respond?
 Understand the radiation doses associated with
various imaging modalities
 Order imaging tests on basis of medical indications,
not because of parental/legal/insurance pressure
 Discuss problem cases with radiologist, engage their
expertise
 Inform parents/patients of radiation risk
www.ImageGently.com
What is the best
(most appropriate) imaging exam?
What are the alternatives?
 First febrile seizure
 First non-febrile seizure
 Headaches
 RLQ abdominal pain
 Acute flank pain with hematuria
 Unusual head shape
 Evaluate vascular ring
Image Gently
One size does not fit all...
There's no question: CT helps us save kids' lives.
But, when we image, radiation matters!
Children are more sensitive to radiation.
What we do now lasts their lifetimes.
So, when we image, let's image gently:
More is often not better.
Image Gently
 When CT is the right thing to do:
 Child size the kVp and mA
 One scan (single phase) is often enough
 Get as much information as possible from the
single phase (IV contrast, enteric contrast)
 Scan only the indicated area
ALARA
 As Low As Reasonably Achievable
 Their future is in our hands.
Questions?