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; 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 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;

Radiation  ionization of molecules Instability  DNA breaks occur Body finds and repairs it Picture taken from : Uzm.Dr.Kamuran Kuş, What is Radiation? Then…. it can either… 1.Repair completely  normal strand 2.Apoptosis 3.Repair incompletely  abnormal transcription/regulation  Potential for cancer induction!!

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:

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, 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 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, Beir 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

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

Therefore, according to LNT model: 1:100  risk of radiation-induced cancer Apply a small increased risk over a large population = public health problem!

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 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 % done at age <18 66% done in Females

Griffey RT., Sodickson A.; Cumulative Radiation Exposure and Cancer Risk Estimates in Emergency Department patients Undergoing Repeat or Multiple CT; AJR:192: , 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

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 /s ; 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