Radiation Risk with Medical Imaging

Quyen HuynhOHSU SOM, MS4

Outline

•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

CT radiation and use•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, 2009Amy 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, 2009Lee 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

Physician and Patient Understanding

•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

From Radiation to Cancer•Radiation ionization of molecules•Instability DNA breaks occur•Body finds and repairs it

Picture taken from : Uzm.Dr.Kamuran Kuş, What is Radiation? http://www.bilkent.edu.tr/~bilheal/aykonu/ay2011/radyasyoning.htm

Then…. it can either…1. Repair completely normal

strand2. Apoptosis3. Repair incompletely

abnormal transcription/regulation Potential for cancer induction!!

Radiation terms

•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

Background Radiation•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

Radiation Dose Levels for Common Radiological Procedures

•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

Estimating Cancer Risk with CTs

•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, 603-607Beir VII: Health Risks from Exposure to Low Levels of Ionizing Radiation; 2006

Estimating Cancer Risk with CTs•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

Rice HE, Frush DP, et al.; Review of Radiation Risks from Computed Tomography: Essentials for the Pediatric Surgeon; Journal of Pediatric Surgery (2007) 42, 603-607Beir VII: Health Risks from Exposure to Low Levels of Ionizing Radiation; 2006

•Linear-No-Threshold (LNT) model• Assumes induction of cancer

proportional to exposure• 1 xray increases risk of

cancer• 2 xrays increases the risk

2x

Estimating Cancer Risk with CTs

Rice HE, Frush DP, et al.; Review of Radiation Risks from Computed Tomography: Essentials for the Pediatric Surgeon; Journal of Pediatric Surgery (2007) 42, 603-607Beir 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

Estimating Cancer Risk with CTs

Rice HE, Frush DP, et al.; Review of Radiation Risks from Computed Tomography: Essentials for the Pediatric Surgeon; Journal of Pediatric Surgery (2007) 42, 603-607Beir 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)

Estimating Cancer Risk with CTs

Rice HE, Frush DP, et al.; Review of Radiation Risks from Computed Tomography: Essentials for the Pediatric Surgeon; Journal of Pediatric Surgery (2007) 42, 603-607Beir 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

Estimating Cancer Risk with CTs

Therefore, according to LNT model: 1:100 risk of radiation-induced

cancer

•Apply a small increased risk over a large population = public health problem!

Estimating Cancer Risk with CTs

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, 2009David 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

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

Estimating Cancer Risk with CTs

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

•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

Ways to decrease radiation to the patient

•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)

On the Frontier….

•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

Summary

•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

Thank You!