Radiology Resident Physics Course George David MS FAAPM FACR Associate Professor of Radiology Augusta University Good Old Days of CT First axial images of live person Dose Who cares Things Changed ID: 933105
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Slide1
Dose Issues in Computed Tomography
Radiology Resident Physics Course
George David MS, FAAPM, FACRAssociate Professor of RadiologyAugusta University
Slide2Good Old Days of CTFirst axial images of live personDose? Who cares?
Slide3Things ChangedAre we killing people with CT?
Slide4Worse still…Are we killing children with CT?
?
Slide56/19/2001
“
Each year, about 1.6 million children in the USA get CT scans to the head and abdomen — and about 1,500 of those
will die
later in life of radiation-induced cancer …”
Approximately 1 in 1000
Slide61 of 1,000 …
Slide7Are We Killing Children?
Really Slow Bullet
30-40 Years
CT Gun
Slide8It Gets WorseOn the basis of data from 1991- 1996, ~ 0.4% of future cancers may be
attributable to radiation from CT.By adjusting this estimate for current CT use, this estimate may go up to
1.5-2.0%.
2007
Computed Tomography — An Increasing Source of Radiation
Exposure
David J. Brenner, Ph.D., D.Sc., and Eric J. Hall, D.Phil., D.Sc.
Slide9It Gets Worse
On the basis of data from 1991- 1996, ~ 0.4% of future cancers may be
attributable to radiation from CT.By adjusting this estimate for current CT use, this estimate may go up to1.5-2.0%.
2007
Based upon calculations.
Not based upon observations!
Slide10100 People Diagnosed with Cancer in 2035
Caused by CT
Slide11How Much Radiation from CT?
From the FDA
Diagnostic Procedure
Typical Effective Dose (mSv)
1
Chest x-ray (PA film)
0.02
Lumbar spine
1.5
I.V. urogram
3
Upper G.I. exam
6
Barium enema
8
CT head
2
CT chest
7
CT abdomen
8
Coronary artery calcification CT
3
Coronary CT angiogram
16
Slide12Does CT Really Kill?
http://library.thinkquest.org/
Diagnostic Procedure
Typical Effective Dose (mSv)
1
Chest x-ray (PA film)
0.02
Lumbar spine
1.5
I.V. urogram
3
Upper G.I. exam
6
Barium enema
8
CT head
2
CT chest
7
CT abdomen
8
Coronary artery calcification CT
3
Coronary CT angiogram
16
Slide13Linear No-threshold ModelNo safe level of radiation
Low Doses are HarmfulModel used for Regulations
Radiation Dose
Biological Effects
Line
Science
Slide14Biological Effect from RadiationHigh dose effects well knownWhat happens at low doses?
Radiation Dose
Biological Effects
?
Known effects
Our
Patients
Us
Slide15Linear ModelIf a 1,000 pound lion can kill 100 Romans in an hour
Slide16Linear ModelA 10 pound puddy tat can kill 1 Roman in an hour.
Oh no!
Suffering succotash… I mean ROAR
*
Slide17Water Can Kill You!!!
H
2
O
Slide18Threshold ModelLow Doses are NOT
Harmful
Radiation Dose
Biological Effects
Things that are dangerous in excess are not dangerous in moderation
Slide19Radiation Hormesis ModelLow Doses are Beneficial
Radiation Dose
Biological Effects
(bad)
(good)
Radiation is good for you!
Slide20Expert Panel Clarification
Linear No-Threshold
Low Doses Can Kill You
Threshold
Low Doses Are Meaningless
Hormeses
Low Doses Are Beneficial,
Nyuk
,
Nyuk
,
Nyuk
Slide212011 CT Summit: “Admit we don't know CT radiation risk”
The linear model should be used for setting radiation protection standards
most conservativeSenseless to use to predict cancer deaths.
Slide22We May Never Know
It's difficult to model cancer risk from radiation at small doses, such as produced by CT. To have enough statistical power to detect such small effects, you need to track > 10 million patients for yearsAt the end of the day
the controversy will never go away.
Cynthia
McCollough
,
Professor
of
Radiologic Physics,
Mayo Clinic
Slide23Linear No-ThresholdFollowing slides from “Radiation Risks of Medical Imaging: Separating Fact from Fantasy
” (Hendee, O’Connor, Radiology August 2012)
Major source of knowledge for health effects to individuals from ionizing radiation
Slide24Hendee & O’Connor“
Most population studies have revealed no or much smaller demonstrable health effects of radiation exposure”<100
mSv, it is not possible to identify increased incidence of cancer with any confidenceLNT model appears to conflict with current understanding of biologic mechanisms
Slide25Hendee & O’Connor (cont.)“Studies of 500,000 occupationally exposed workers in the nuclear industry … demonstrated reduced cancer
BEIR VII largely excludes these studies from its analyses”Claimed exposed population in better health than general population
Beir
VII:
“
Because of limitations in the data
…,
risk estimates are uncertain,
&
estimates
… 2 -3 X
larger or smaller cannot be excluded.
”
Slide26Why All the Attention?USA TodayBrenner / Hall Article
CT “accidents”Increase in CT usage
Slide27Cedars-Sinai CT OverexposuresBrain perfusion studiesRepeated exposure to same anatomy
Table didn’t moveNo equipment defectsProtocols alteredDecreased image noise
Caused mA/dose to increase X 8Problem not identified for 18 months!!!
Slide28Slide29Any wonder our patients/parents are concerned?
Slide30Medical imaging procedures should be appropriate & conducted at the lowest radiation dose consistent with acquisition of desired information
Discussion of dose risks should be accompanied by acknowledgement of procedure benefits
Slide31Risks of medical imaging at effective doses < 50
mSv
(5 rad) for single procedures or 100
mSv
(10 rad) for multiple procedures over short time periods are
too low to be detectable & may be nonexistent.
Predictions of hypothetical cancer incidence and deaths in patients exposed to such low doses are
highly speculative
should be discouraged
Slide32