Quyen Huynh
OHSU SOM, MS4
•CT radiation and use
•Physician and patient understanding
•Radiation terms
•Cancer Risk with CTs
•Ways to decrease radiation to the patient
•Summary
Although there are many types of medical imaging……
The focus of this talk will be on: CT
(Computed Tomography) imaging
• High rates of use
• Higher amounts of radiation exposure
•Why is it important?
•RISK vs. BENEFIT
•Important to understand how much radiation medical imaging
delivers
•Increasing
use of CTs in healthy individuals
•Risk of potential cancer may outweigh diagnostic value
•The threshold for CT use has DECLINED
•3-fold increase in CT use since 1993 (~70 million
scans/year in the US)
•Use of CTs even when imaging results may not change
medical management
Rebecca Smith-Bindman, MD et al; Radiation Dose Associated with Common Computed Tomography Examinations and the Associated Lifetime Attributable Risk of Cancer; Arch Intern Med/Vol 169
(No.22), Dec 14/28, 2009
Amy Berrington de Gonzalez, Dphil et al; Projected Cancer Risks from Computed Tomographic Scans Performed in the United States in 2007; Arch Intern Med/Vol 169 (No.22), Dec 14/28, 2009
Lee Cl, Haims AH, Monico EP, et al. Diagnostic CT Scans: assessment of patient, physician, and radiologist awareness of radiation dose and possible risks. Radiol. 2004;231;393-398 Emergency Radiology
2006 Oct: 13(1):25-30
•2004 survey,
•most Radiologists and ED Physicians
underestimated actual CT radiation dosage by a
factor of 10.
•Literature
estimates 1 Abd CT scan equivalent to 100-250 chest
radiographs
•Only ~7% of patients were informed of risks and
benefits
Lee Cl, Haims AH, Monico EP, et al. Diagnostic CT Scans: assessment of patient, physician, and radiologist awareness
of radiation dose and possible risks. Radiol. 2004;231;393-398
•Radiation ionization of molecules
•Instability DNA breaks occur
•Body finds and repairs it
Then…. it can either…
1. Repair completely  normal strand
2. Apoptosis
3. Repair incompletely abnormal
transcription/regulation 
Potential for cancer induction!!
Picture taken from : Uzm.Dr.Kamuran Kuş, What is Radiation? http://www.bilkent.edu.tr/~bilheal/aykonu/ay2011/radyasyoning.htm
•Exposure – ability of xrays to ionize air (Roentgens (R))
•Absorbed radiation dose – amount of energy absorbed
per unit mass at a specific point (grays or rads)
•Effective dose – takes into account where the radiation
dose is being absorbed and gives a weighted average of
organ doses
McNitt-Gray MF, AAPM/RSNA Physics Tutorial for Residents: Topics in CT: Radiation Dose in CT; Radiographics 2002;
22:1541-1553
•Average worldwide
individual exposure to
background radiation
per year = ~2.4 mSv
•~52% of that is from radon
in our homes
•Those in Denver, CO will
have 50% more
•altitude dependent
Beir VII: Health Risks from Exposure to Low Levels of Ionizing
Radiation; 2006
•Chest Xray
•~0.1mSv
•~10 days background radiation
•CT Head
•~2mSv
•~8 months background radiation
•CT Chest
•~7mSv
•~2 years background radiation
•CT Abd/Pelvis
•~15mSv
•~5 years background radiation
Safety X-ray; radiologyinfo.org
•Small increased risk of cancer from
radiation exposure difficult to prove
•Mathematical models extrapolated from
studies of radiation exposure
Rice HE, Frush DP, et al.; Review of Radiation Risks from Computed Tomography: Essentials for the Pediatric Surgeon; Journal of Pediatric Surgery
(2007) 42, 603-607
Beir VII: Health Risks from Exposure to Low Levels of Ionizing Radiation; 2006
•BEIR VII Risk Model
•Hiroshima Atomic bomb survivors
•Cohort study
•~120,000 persons followed from 1950-2000
•Mathematical model established Linear-No-Threshold
(LNT) relationship
•Linear-No-Threshold (LNT) model
•Assumes induction of cancer
proportional to exposure
•1 xray increases risk of cancer
•2 xrays increases the risk 2x
Rice HE, Frush DP, et al.; Review of Radiation Risks from Computed Tomography: Essentials for the Pediatric Surgeon; Journal of Pediatric Surgery (2007) 42, 603607
Beir VII: Health Risks from Exposure to Low Levels of Ionizing Radiation; 2006
Keeping it in perspective…
•Baseline lifetime risk of cancer is quite high:
•~42%
in the general population
Rice HE, Frush DP, et al.; Review of Radiation Risks from Computed Tomography: Essentials for the Pediatric Surgeon; Journal of Pediatric
Surgery (2007) 42, 603-607
Beir VII: Health Risks from Exposure to Low Levels of Ionizing Radiation; 2006
Keeping it in perspective…
•42% Baseline lifetime risk
In other words….
Of 100 people 
(represented by all the
circles in this box)
•~42 people will be
diagnosed with
cancer (causes
unrelated to
radiation)
(Green-filled circles)
Rice HE, Frush DP, et al.; Review of Radiation Risks from Computed Tomography: Essentials for the Pediatric Surgeon; Journal of Pediatric
Surgery (2007) 42, 603-607
Beir VII: Health Risks from Exposure to Low Levels of Ionizing Radiation; 2006
And
~1 person could
be diagnosed
with cancer
resulting from a
dose of 100mSv
radiation
Rice HE, Frush DP, et al.; Review of Radiation Risks from Computed Tomography: Essentials for the Pediatric Surgeon; Journal of Pediatric
Surgery (2007) 42, 603-607
Beir VII: Health Risks from Exposure to Low Levels of Ionizing Radiation; 2006
Therefore, according to LNT model:
1:100  risk of radiation-induced cancer
•Apply a small increased risk over a large
population = public health problem!
Some general stats….
•29,000 incident cancers/year estimated could be related to CT scans
•Equates to ~2% of all cancers in the US
•Largest contribution are from scans of the: abd/pelvis, chest, head
•Average lifetime attributable risk of a radiation-induced cancer is 1:1000 patients
receiving 10mSv effective dose (~abd/pelvis CT)
•Half of these expected to be fatal
•Most common projected radiation-related cancer are:
•lung, colon, leukemia
•35% of projected cancers are due to scans done at the age of 35-54
•15% done at age <18
•66% done in Females
Amy Berrington de Gonzalez, Dphil et al; Projected Cancer Risks from Computed Tomographic Scans Performed in the
United States in 2007; Arch Intern Med/Vol 169 (No.22), Dec 14/28, 2009
David J. Brenner, Ph.D, D.Sc, and Eric J. Hall, D.Phil., D.Sc; Computed Tomography – An Increasing Source of Radiation
Exposure; NEJM 357;22, November 29, 2007
•Younger patients
•Radiation risk is greater! Why?
•Increased
radiosensitivity of their organs
•larger amt of dividing cells
•More years of remaining life
•More time in which cancer may develop
Griffey RT., Sodickson A.; Cumulative Radiation Exposure and Cancer Risk Estimates in Emergency Department patients
Undergoing Repeat or Multiple CT; AJR:192:887-892, April 2009
•Decrease the # of procedures performed
•Reduce CT-related dose in individual patients
•Adjust dose according to patient profile, size,
BMI, etc..
•Replace CT use with other options (US, MRI)
•Record and monitor CT-related radiation dose
•Awareness of patient overexposure to medical radiation
•Helps decide if the patient is at high risk
•Useful for educating patients
•Road blocks
•Complicated algorithm to correctly estimate whole-body
effective dose
•Multiple EMRs across institutions (multiple software
compatibilities, lack of consistency with protocols and labels)
Cook TS, Zimmerman SL, et al.; An Alogrithm for Intelligent Sorting of CT-related Dose Parameters; J Digit Imaging;
DOI 10.1007/s10278-011-9410-1; 2011
•Potential public health concern
•Risks vs. Benefits needs to be evaluated with
EVERY CT scan
•Patients need to be informed of risks vs. benefits
•Find ways to decrease radiation exposure in
patients