Transcript ď - Philip F. Judy

IS THERE A RATIONAL
APPROACH TO RADIATION
RISK?
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Philip F. Judy Ph.D.
Department of Radiology
Brigham and Women's Hospital
New England AAPM Chapter Meeting
February 15, 2008
Invitation from Robert Cormack
“One subject that is of interest to the group is
the safety of low diagnostic levels of
radiation especially after the recent paper in
NEJM. Lee Chin mentioned that you would
be well suited to speak about this issue, and
I've always appreciated your viewpoint in
the BWH RSC meetings.”
Phil Judy response:
• Many in this audience are more qualified to
speak.
• Whether I am well suited, time will tell.
• Robert may not completely appreciate the
basis for my “viewpoint” at BWH Radiation
Safety Committee meetings.
My comment at a 1974 PPBH
Radiation Safety Committee Meeting
• Informed consent for a radiation study requires the
statement that the radiation exposure will result in
an increased risk of cancer. Without such a
statement the consent is not informed.
• The committee’s response has been no way can
such a statement could be included in the
informed consent, because there will be no
volunteers for research protocols involving
radiation exposure.
2008 Risk statement from a
consent form – No real change
from 1974
“A portion of this study will involve exposure to
radiation for research purposes. The radioactive
drug study proposed will expose you to 0.7 rem (a
rem is a unit of radiation dose). This is equivalent
to 14 % of the 5 rem annual limit for a person who
works with radiation, or 3 times the natural
environmental radiation the average person
receives in the United States annually.”
Basis for my position
• Statement by Eric Hall in his textbook:
Radiobiology for the Radiologist – page 145.
• “The belief that stochastic effects have no dose
threshold is based on the molecular mechanisms
involved. There is no reason to believe that even a
single x-ray photon could not result in a base
change leading to a mutation that could cause
cancer or a hereditary defect.”
Computed Tomography
An Increasing
Source of Radiation Exposure
David J. Brenner, Ph.D., D.Sc., and Eric J.
Hall, D.Phil., D.Sc.
New England Journal of Medicine
2007;357:2277-84.
Brenner and Hall, NEJM, 2007
“In summary, there is direct evidence from
epidemiologic studies that the organ doses
corresponding to a common CT study (two
or three scans, resulting in a dose in the
range of 30 to 90 mSv) result in an
increased risk of cancer. The evidence is
reasonably convincing for adults and very
convincing for children.”
Do you believe that radiation
exposure from a CT exam increases
an individual’s risk of cancer?
• Respond now!
Brenner and Hall, NEJM, 2007
“In a recent survey of radiologists and
emergency-room physicians … 53% of
radiologists and 91% of emergency-room
physicians did not believe that CT scans
increased the lifetime risk of cancer.”
Why change in Eric Hall’s
argument from molecular
mechanism to direct evidence?
• Radiation exposure from CT exams is
considerable large than projection radiographs.
• Multi-detector CT has lead to several scans
becoming part of standard CT exams.
• CT exams are repeated.
• Radiation exposures have increased so direct
evidence applies!
Some evidence that radiation
exposure from CT exams is
considerable larger than projection
radiographs.
Dose - Typical Exams
BWH
Abdomen/Pelvis Exams
• Radiographic
Single film
• CT
Single scan
ESD (mGy)
2.5 - 4.5
CTDI (mGy)
18
Eff. Dose (mGy)
0.44 - 0.71
Eff. Dose (mGy)
6.4
Nawfel RD, Judy PF, Schleipman AR, Silverman SG. “Patient
radiation dose at CT urography and conventional urography,”
Radiology 2004 Jul;232(1):126-32
Risk of Radiographic
Examinations of Chest
Lifetime probablity of excess cancer
0.0020
Diagnostic CT
Lung Cancer Screening CT
PA chest radiograph
0.0018
0.0015
0.0012
0.0010
0.0007
0.0005
0.0002
0.0000
20
30
40
50
60
70
80
Age
Judy PF. “Multidetector-row CT image quality and radiation
dose: imaging the lung,” Semin Roentgenol 2003
Apr;38(2):186-92.
http://www.fda.gov/cdrh/ct/risks.html
Diagnostic Procedure
Typical
Effective Dose
Number of Chest
X rays (PA film)
Time Period -Natural
Background Radiation
(mSv)
Chest x ray (PA film)
0.02
1
2.4 days
Skull x ray
0.07
4
8.5 days
Lumbar spine
1.3
65
158 days
I.V. urogram
2.5
125
304 days
Upper G.I. exam
3.0
150
1.0 year
Barium enema
7.0
350
2.3 years
CT head
2.0
100
243 days
CT abdomen
10.0
500
3.3 years
Image Quality
Patient Radiation
Dose
Measurement
&
Prediction
Risk
&
Benefi
Risk and Benefit
• Estimate radiation risk and benefit from
CT protocols
– Determine characteristics of cases (e.g., age,
sex, purpose of exam, and exam frequency)
– From effective dose calculate excess
mortality associated with radiation exposure
(individual and population)
– Determine benefits and non-radiations risks
of the outcomes of the imaging exam.
Purpose of human radiation exposure
(case classification)
• Research - no benefit to individual – other
individuals in future may get benefit
• Screening – individual may get benefit but
typically others will get benefit
• Diagnosis – benefit to individual
• Cancer staging and treatment evaluation – benefit
to individual
• Image guided treatment – benefit to individual
• Combinations of above – usually clinical trials