Radiology Resident Physics Course Dose Issues in Computed Tomography 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 Are we killing people with CT?

Worse still… Are we killing children with CT? ?

6/19/2001 “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

1 of 1,000 …

Are We Killing Children? Really Slow Bullet 30-40 Years CT Gun

It Gets Worse 2007 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 to 1.5-2.0%. Computed Tomography — An Increasing Source of Radiation Exposure David J. Brenner, Ph.D., D.Sc., and Eric J. Hall, D.Phil., D.Sc.

2007 It Gets Worse Based upon calculations. 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 to 1.5-2.0%. Based upon calculations. Not based upon observations!

100 People Diagnosed with Cancer in 2035 Caused by CT

How Much Radiation from CT? 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 Coronary artery calcification CT Coronary CT angiogram 16 From the FDA

Typical Effective Dose (mSv)1 Does CT Really Kill? 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 Coronary artery calcification CT Coronary CT angiogram 16 http://library.thinkquest.org/

Linear No-threshold Model No safe level of radiation Low Doses are Harmful Model used for Regulations Line Biological Effects Science Radiation Dose

Biological Effect from Radiation High dose effects well known What happens at low doses? Biological Effects Known effects Our Patients ? Us Radiation Dose

Linear Model If a 1,000 pound lion can kill 100 Romans in an hour

Suffering succotash… I mean ROAR Linear Model * A 10 pound puddy tat can kill 1 Roman in an hour. Suffering succotash… I mean ROAR Oh no!

Water Can Kill You!!! H2O

Things that are dangerous in excess are not dangerous in moderation Threshold Model Low Doses are NOT Harmful Things that are dangerous in excess are not dangerous in moderation Biological Effects Radiation Dose

Radiation Hormesis Model Low Doses are Beneficial Radiation is good for you! Biological Effects (bad) (good) Radiation Dose

Expert Panel Clarification Linear No-Threshold Threshold Hormeses Low Doses Are Beneficial, Nyuk, Nyuk, Nyuk Low Doses Are Meaningless Low Doses Can Kill You

2011 CT Summit: “Admit we don't know CT radiation risk” The linear model should be used for setting radiation protection standards most conservative Senseless to use to predict cancer deaths.

We 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 years At the end of the day the controversy will never go away. Cynthia McCollough, Professor of Radiologic Physics, Mayo Clinic

Linear No-Threshold Following 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

Hendee & 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 confidence LNT model appears to conflict with current understanding of biologic mechanisms

Hendee & 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.”

Why All the Attention? USA Today Brenner / Hall Article CT “accidents” Increase in CT usage

Cedars-Sinai CT Overexposures Brain perfusion studies Repeated exposure to same anatomy Table didn’t move No equipment defects Protocols altered Decreased image noise Caused mA/dose to increase X 8 Problem not identified for 18 months!!!

Any wonder our patients/parents are concerned?

Medical 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

Risks 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