What Me Worry? The Cancer Risks from CT Scans

1. What Me Worry?The Cancer Risks from CT Scans Irene Hendrickson, M.D. PPMC Medical Grand Rounds November 26, 2008

2. Patient, “Jane” • 26 year-old female • PMH multiple presentations to clinic and to ED for abd pain, headaches, dizziness, hematuria. Also has anxiety and, often, a generally positive ROS. • Radiation exposures: • 4/06 IVP for hematuria • 4/06 renal CT for hematuria, flank pain • 3/07 CT of head for dizziness • 5/07 CXR SOB, cold sxs • 8/07 CT of abd • 8/07 CT-guided kidney biopsy • 9/07 renal CT for flank pain after biopsy • 12/07 CT abd for abd pain

3. Headlines

4. “…increased usage and cumulative dosage from exams that involve radiation exposure have led to a growing concern about potential risks of cancer induction.” “As the ordering physician you can help minimize radiation exposure for your patients...”

5. Objectives • Review radiation exposure associated with CT scans. • Discuss potential malignancy risks associated with increased use of CT scans, both individual and population-based. • Reflect on physician practices and decision-making that can minimize radiation risks to patients.

6. Two main points: • There is an increasing use of CT scans (millions) and increasing potential uses. • Radiation from CT scan is much greater than plain films

7. “CT has become ubiquitous” 2006: 67 million scans • Improved technology • Speeded procedures • Growing list of uses • Proliferation of machines Pediatric scans: 1989 = 4% 1993 = 6% 2000 = 11% • Adult Screening: • CT colonography • CAD • Lung cancer screen • Full Body 1980: 3 million scans

8. Widely adopted new technology “Despite concerns about low sensitivity of CTPA… its adoption has been rapid.” V/Q vs CTPA. • “Non-inferiority study”. • CTPA not inferior to V/Q • V/Q scans still have a role to play for PE.: “involves much less radiation exposure… than CTPA.” • Normal V/Q excludes PE • nondiagnostic V/Q + neg u/s +Wells <4.5 excludes PE “Clinicians have been attracted to CTPA use because it provides a clear result (either positive or negative) and because it may detcet alternative… causes of patients’ symptoms.” Dec 2007

9. NEJM 2007;357:2277-84

10. Sources of Radiation exposure in the United States Total Daily Background Radiation: 0.007 mSv per day United States Nuclear Regulatory Commission

11. Radiation Dose Comparison From www.fda.gov

12. Definitions Absorbed Dose: describes the effects of radiation in a tissue or organ (energy deposited/unit mass) 1 joule/kg = 1 gray (Gy) Equivalent Dose: describes the biological effects of an absorbed dose and the amount of radiation absorbed. Absorbed dose (in Gy) averaged over an organ and adjusted for the radiation Absorbed dose (in Gy) X radiation weighing factor = sievert (Sy) Effective Dose: The risk of cancer induction from an equivalent dose depends on the organ. “tissue-specific weighting factor” accounts for the variation. a calculated quantity estimating the uniform, whole-body equivalent dose that would produce the same level of risk for adverse effects (Sy) Information comes from measured data and from calculated data.

13. Radiation dose variables Doses are dependent on factors: Number of scans (patients get more than one on same day) Size of patient Tube current and scanning time in milliampseconds (mAs) Axial scan range Scan pitch (degree of overlap between CT slices) Specific scanner designs.

14. Biologic effects of ionizing radiation • Large doses (Hiroshima and Nagasaki bombs, Chernobyl accident) • 800-16,000 mSV • Acute radiation sickness, immediate cell/tissue/organ damage • Low doses • Less than 100 mSV spread over time • Radiation knocks electrons from their orbits, creating ions. • Hydroxyl radicals interact with DNA to cause strand breaks or base damage: • Point mutations • Chromosomal translocations • Gene fusions

15. Risks at low doses of radiation • Atomic-bomb survivor subgroups with low radiation (5 to 150 mSv) • Significant increase in overall risk of cancer • Cohort of 86,000 atomic bomb survivors • Solid cancer incidence over 47 years of follow-up: >13,000 • 6.3% attributed to radiation • Solid cancers deaths: 9,335 • 5% estimated to be radiation-related • Equivalent to radiation of a typical CT study of 2-3 scans in an adult Radiation Effects Research Foundation in Radiation Research Oct 2003

16. Lifetime risk for incidence of solid cancer and leukemia If 100 people exposed to 0.1 Gy (100 mGy), expect: • 1 cancer from this exposure • 42 cancers from other causes Douple, Evan, The National Academies. Biological Effects of Ionizing Radiation “A summary of BEIR VII”

17. Risks at low doses of radiation Other Epidemiologic Findings: • Occupational exposures • Nuclear industry workers • UK National Registry of Radiation Workers study • Environmental exposures • Medical Exposures

18. Strengths of A-bomb Survivor Study for Use in Risk Assessment • Large population size • All ages and both sexes • Long term follow-up for both mortality and cancer incidence • Whole body exposure • Well-characterized dose estimates for individual study subjects • Useful range of doses Douple, Evan, The National Academies. Biological Effects of Ionizing Radiation “A summary of BEIR VII”

19. Lifetime Cancer Deaths Associated with CT scans Head CT Abdominal CT 25 yo: <0.01% 25 yo: <0.06% Brenner DJ, NEJM2007;357:2277-84

20. Multiple CT scans • Almost all patients having CT scans of abd or pelvis had more than 1 CT scan on same day • For all pts having CT scans: • 30% had 3 scans • 7% had 5 scans • 4% had 9 + scans Mettler et al, CT scanning: patterns of use and dose. J Radiol Prot 2000

21. “Jane” Total Equivalent Background Dose: 16.2 years Total Increased Cancer Death: 0.32%

22. Risks and Benefits • Important to distinguish between individual risks and collective, public-health risks • The individual risks are small, so the benefit / risk ratio for any patient will generally be very large • But the exposed population (~64 million patients/yr in the US) is large • Even a very small individual radiation risk, when multiplied by a large (and increasing) number of patients, is likely to produce a significant long-term public health concern >20,000 CT-induced cancers per year Up to 2% of annual US cancers

23. Some critiques…. • Can dose estimates from atomic bomb survivors be extrapolated to medical imaging? • Can cancer development in Japanese population be extrapolated to US population? • Assumptions that may overestimate risk: • Estimated CT scan radiation doses • Estimates of excess cancers has wide confidence interval

24. What Me Worry? Concerns arise when: • CT exams are used without proven clinical rationale • Alternative modalities could be used with equal efficacy • CT scans are repeated unnecessarily “Any unneededradiation is too much”

25. Increased utilization, esp in traumas, EDs, chronic conditions, repeat imaging for monitoring of conditions Defensive medicine System and procedural inefficiencies Poor communication between providers Lack of physicians awareness of previous scans Public demand for high-end technical exams Up to 1/3 of CT scans may be unnecessary Pediatr Radiol 2002, AJR 2005

26. Worthless CT scans? Systems and Procedures: Initial “non-contrast” CT to save time, but when nothing found, return the patient for a “real” CT with contrast. Patients with inadequate IV sites result in useless contrast injections Patient ends up getting re-scanned a day later with better IV access.

27. CT scan use continues to grow Interest in mass CT screening in asymptomatic adults: • Screening for colon polyps (virtual colonoscopy) • Screening for early-stage lung cancer in smokers and ex-smokers • Screening for cardiac disease • Screening the whole body (full body screening)

28. Adult CT Screening of Asymptomatic Patients No demonstrated effectiveness Medical professional societies have not endorsed * Except CTC - March 2008 Benefit to high-risk individuals for specific diseases (CAD, lung CA, colon CA) is currently being studied Efficacy, as with other general screening modalities Added issue of radiation exposure and potential cancer risks

29. Direct-to-consumer marketing: CT and MR screening of asymptomatic patients • Newspapers and brochures for consumers analyzed for their messages • Conclusions: lacks information on uncertainties and risks associated with imaging • “References to the potential risk of irradiation associated with CT scans were also notably missing…” • Companies for MRI “make explicit reference to the nonradiation modality.” Illes J, et al. Arch Int Med 2003

30. Involves paired scan (prone/supine position) Has the potential to increase compliance for colorectal screening Can be performed with lower radiation doses than other CT Joint Guideline: The American Cancer Society, the US multi-Society task force on colorectal cancer and the American College of Radiology Average-risk patient Starting Age 50 Every 5 years Virtual Colonoscopy

31. Virtual Colonoscopy If screening were standard for age over 50, the potential “market” would be 100 million people in the US. Gastroenterology 2005: • Benefit-risk ratio is potentially large • Cancer Risk 0.14%. Brenner, Georgsson, Gastroenterology 2005. Mass Screening With CT Colonography: Should the Radiation Exposure Be of Concern?

32. Lung Cancer Screening with CT Early reports of success in finding small lung tumors with spiral CT scans sparked widespread enthusiasm. (Lancet 1999;354:99-105) • Concluded that spiral CT scans greatly improve detection of lung cancer “at an earlier and potentially more curable stage.” • Generated extensive medial coverage • Public interest led to early adoption of scans • Many marketing efforts to smokers via newspapaer, TV, billboards

33. Lung Cancer Screening with CT • NEJM 2006: lung CA had 10 yr survival approaching 90% if detected by CT • Arch Int Med Nov 2007: “Overstating the evidence for lung cancer screening” authors do not agree that lung CA screening has been shown to have more good than harm

34. Lung Cancer Screening with CT National Lung Cancer Screening Trial currently underway in US (Vastag B. Lung screening study to test popular CT scans. JAMA 2002;288:1705-6) • Eight-year study, began 2002 • will examine the risks and benefits of spiral CT scans compared to chest X-rays in lung cancer screening • CT or CXR yearly x 3 years

35. Lung Cancer Screening and CT Radiation Risks • Screening technique involves “low dose” protocol compared with standard CT lung scans • Smokers may be more susceptible to radiation cancer risk. • Radiation-induced cancers generally decrease with age exceptlung cancers, which may increase with age • 50 year old smoker, annual screening CT, radiation lifetime lung cancer risk = 0.5%. • Baseline lung cancer risk = 14%

36. CT –based Cardiac Screening • Coronary artery calcification by CT or CT angiography • High organ doses of radiation, lung and breast • CT coronary angiography = 40-100 mGy • CT-based calcium scoring = 10 mGy • Information obtained when heart in diastole • dose delivered during other parts of heart cycle is effectively wasted

38. CT- based cardiac screening Screening for Heart Attack Prevention and Education (SHAPE), 2006 • Panel of cardiologists convened by “Association for Eradication of Heart Attack” • Call for non-invasive screening (CT or u/s) • All asymptomatic men (45-75) years and women (55-75 years) • In US = 61 million people

39. Estimated radiation-associated mortality risks for multidetector row CT calcium score The total predicted lung cancer deaths is ~7000 out of the 61 million screened (about 1/8000) Hall and Brenner, Brit J Rad 2008

40. Full-Body CT Screening Hall and Brenner, Brit J Rad 2008

41. “We recommend therefore that services offering whole body CT scanning of asymptomatic individuals should stop doing so immediately”

42. Two main points: There is an increasing use of CT scans (millions) and increasing potential uses. Radiation from CT scan is much greater than plain films

43. Can CT usage be reduced? • Can other imaging modalities replace CT usage without loss of efficacy? • Known kidney stones: u/s + abd xray • AAA screening: ultrasound • Presurgical diagnosis of appendicitis • Need for continuing physician education on imaging modalities

44. “provide…guidance for nonradiology house staff regarding both the risks associated with radiation and the appropriate clinical indications for imaging”

45. Acute Abdominal Pain Appropriateness rating 1-9

46. Can CT usage be reduced? Eliminate “worthless” CT scans Improve communication between physicians Optimize use of EMR Develop point-of-care decision support

47. Electronic Orders, protocols “Patient must have a peripheral IV access (18g preferred.) Only “Power PICC” accepted for central line access.”

48. 63 year-old female, chronic pancreatitis

49. Can CT doses be reduced? • In general, lower CT image noise = higher radiation doses • Tailored protocols • Are pre- and post-IV contrast scans necessary? • Are arterial and portal venous post-contrast scans necessary? • Low dose protocols • Renal colic, CT colonography, follow-up lung mass

50. Can CT doses be reduced? For the ordering physician • “Diagnosis NOT aesthetics” • Communication with the radiologist