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PET/CT, Cardiac CT, Colonography CT : A New IAEA Safety Report Series

PET/CT, Cardiac CT, Colonography CT : A New IAEA Safety Report Series. Dawn Banghart, CHP Sr. Health Physicist/Alternate Radiation Safety Officer Stanford University . Introduction. The IAEA Safety Report Series recently published No. 58, 60 and 61 to address safety issues in: PET/CT (58)

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PET/CT, Cardiac CT, Colonography CT : A New IAEA Safety Report Series

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  1. PET/CT, Cardiac CT, Colonography CT : A New IAEA Safety Report Series Dawn Banghart, CHP Sr. Health Physicist/Alternate Radiation Safety Officer Stanford University

  2. Introduction • The IAEA Safety Report Series recently published No. 58, 60 and 61 to address safety issues in: • PET/CT (58) • Cardiac CT (60) • Virtual Colonography (61) • This talk will encapsulate key principals and standards highlighted in these reports and raise the question: • Is it possible to write a comprehensive document in this changing technological environment?

  3. Learning objectives: • After this talk you will be able to: • Site the average effective dose for CT Colonography, Cardiac CT and whole body PET/CT • Askthree very good PET/CT dose optimization questions to raise awareness in the clinical setting • List dose reduction strategies for PET/CT staff • Compare CT Colonography to conventional endoscopy

  4. IAEA Safety Reports Series • Four international organizations collaborated to produce reports 58, 60 & 61 : • The International Atomic Energy Authority • The World Health Organization • The International Society of Radiology • The International Commission on Radiological Protection • The reports provide guidance and advice for those involved in some of the more dose-intensive areas emerging in radiology and cardiology today

  5. Report General Comments • Pet/CT (No. 58) directed towards patient AND staff radiation protection • Cardiac CT (No. 60) and Virtual Colonography (No. 61) directed towards patient radiation protection ONLY • All three identify • Rapid industry growth • Sharp increase in patient effective dose since the emergence of CT technology (1970s) and PET technology (2001) • Expanded applications (e.g., in psychiatry, infection imaging)

  6. Rapid industry growth?Improvements in Technology CT use has increased from 3 million scans in 1980 to 62 million a year currently (including 4 million kids) Circa 1975 Present-day, shows six-fold increase in detail (images courtesy Siemens Medical Systems and Imaginis.com)

  7. Beyond new Technology what’s up with dose?Increasing Obesity 1960 - 2000 From CDC's Diabetes Systems Modeling Project

  8. What’s up with increased applications? Over the 20th century, the older population grew from 3 million to 35 million

  9. Increased CT Scans in Children • CT scans in children significantly increased between 2004 and 2006 and comprised approximately 8–10 % of the total number of CT scans in the USA(1) • According to a Duke study from 2000 to 2006, pediatric ED patient volume increased by 2%, triage acuity remained stable (2) • From the same study, pediatric ED number of scans increased • Chest by 435% • Cervical spine CT by 366 % (2) • Children are at greater risk from a given dose of radiation compared with adults due to increased radiosensitivity of their bodies and a greater period of time in which to manifest these changes(1).

  10. What All 3 Reports Share • Primary concern – • Cancer induction from PET/CT and CT imaging • Patient benefits from PET/CT and CT imaging will have to be balanced against “the cost of the radiation burden to the individual patient, and possibly to the community” • General Aspects of PatientRadiation Protection are directed by identifying the practice, justifying and optimizing the practice. The “must dos”: • Use of radiation in medicine must do more good than harm (i.e., The procedure should improve diagnosis) • Reasonable measures must be employed to improve protection and decrease exposure • Individual cancer risk seems low compared to spontaneous incidence, however, there is room for improvement with respect to radiation dose exposures to the patient

  11. IAEA Safety Report Series No. 58 Radiation Protection in Newer Medical Imaging Technologies: PET/CT - Extracted Gems • Cautions against using effective dose (whole body dose) to estimate cancer detriment • The effective dose intent was to estimate detriment to a population (specifically workers exposed to radiation) • Effective dose intended for whole body exposure, not partial exposure (e.g., cardiac scan, head scan) • Note: Both effective dose and organ dose are estimated using phantoms or via Monte Carlo calculations • Pediatric patient effective dose may be underestimated • Patient-specific dose information can not be obtained due to height, weight and age considerations

  12. Safety Report Series No. 58 Extracted Gems continued • “Dose assessment in CT is challenging” !! • On a practical level for patient dose management Report Series No. 58 provides three very good questions to help raise awareness of dose in the clinical setting: • Is a high quality CT scan for PET/CT needed for diagnosis or therapy management? • Can previously acquired anatomical data be used for correlative interpretation of PET? • Can the low dose CT scan be replaced by the contrast enhanced diagnostic CT scan? • Quoting from the report’s page 20, “image quality in CT often exceeds the clinical requirements”

  13. Case in Point - Cedars-Sinai • Cedars-Sinai error attributed to a "misunderstanding" about an incorrectly programmed CT machine, remained unchecked for 18 months, involved 206 people • Exacerbated nationwide concerns that patients are exposed to excess radiation during medical testing • It appears as though Cedars-Sinai group lowered the noise ratio which automatically increased mA setting • The chief executive said manufacturerscould help prevent future errors by • Improving internal settings and by • Installing more safeguards

  14. Typical effective dosesWhole body w/10 mCi FDG Figure 5. Safety Report Series No. 58 Note: Effective dose refers to the detriment to the whole body

  15. Staff PET Radiation Protection • Nuclear medicine technicians receive about 0.3 – 0.4 mSv whole body per month performing the usual nuclear medicine protocols minus PET (Note: Radiology Technicians receive “minimal” exposures) • Technicians dedicated to PET patients will see as high as 3 times the above average • Main Sources of Radiation • Patient handling • Unshielded radiopharmaceuticals • The patient toilet (you know its true!) • Tasks with greater radiation exposure: • Drawing the dose • Patient positioning on the scanner bed

  16. Staff Dose Reduction Strategies • Exposures to PET radiopharmaceuticals can be minimized through: • Good facility design • Good practice (e.g., conduct patient interviews before injection, use shield carrier to transfer dose) • Use unit dose syringes (bulk doses lead to higher hand exposures) • Provide patient instructions/ensure patient cooperation (e.g., remind to bring warm clothing, any prescribed pain medication, to leave PET center when done) • Minimize time and increase distance by using remote video cameras and audio communication

  17. Question 1 • Of the below dose reduction strategies which task might most reduce a nuclear medicine technician’s exposure? • a. Using a shield carrier to transfer dose • b. Conduct patient interviews before lunch • c. Patient positioning on the scanner bed • d. Shielded radiopharmaceuticals

  18. Question 1 The Correct Answer is c. Patient positioning on the scanner bed

  19. IAEA Safety Series Report Series: No. 60 - Radiation Protection in Newer Medical Imaging Techniques: Cardiac CT • For several reasons it seems likely that pressures will develop to apply new Cardiac CT technologies: • Coronary disease is major of cause death in many countries • Accumulation of calcium in coronary arteries may predict a future heart attack or other heart disease • Technologies (cardiac CT) are now available to monitor the calcification of the coronary arteries • Aging populations for western countries is increasing

  20. The Score on Cardiac CT • Some authors suggest the use of CT calcium scoring in healthy 40-50 year old subjects • Calcium scoring may be helpful in behavior modification programs (i.e., routine follow-up CT scans) • Applications of CT coronary angiography • Can obviate need for invasive catheterization (and its risks) • Evaluation of artery abnormalities • Bypass graft condition • Surgical planning

  21. Effective Doses (mSv)

  22. Effective dose (mSv) compared to other common procedures Table 2.

  23. Risk to the patient from Cardiac CT scanning • Induction of cancer • Note: epidemiological studies have not demonstrated excess risk of cancer induction at doses less than 100 mSv • However as the number of procedures per individual increases the closer that individual gets to the 100 mSv dose • Authors (3) consider the cumulative effective dose of 50 cardiology patients. “On average, each patient underwent a median of 36 examinations … Three types of procedures were responsible for 86% of the total collective effective dose: • Arteriography and interventional cardiology (12% of examinations, 48% of average dose per patient); • Nuclear medicine (5% of examinations, 21% of average dose per patient • CT (4% of examinations, 17% of average dose per patient).” • Median cumulative effective dose was 60.6 mSv

  24. Cardiac CTPatient Safety Considerations • Based on cumulative exposures and higher dose techniques professional societies view the level of detriment set against benefits is too tenuous to warrant use of cardiac CT in mass screening programs • Less frequent referrals with identified risk profiles (combined with dose reduction methodology) provides a more favorable risk-benefit profile

  25. Safety Series Report 61: Radiation Protection in Newer Medical Imaging Techniques: CT Colonography (CTC) • The report proposes that CTC might be applied for the screening of symptom free patients (but is this “justified” - does CTC benefit outweigh harm?) • Colorectal cancer is the second leading cause of deaths from cancer (Europe and USA) • Screening programs may decrease fatality by 15-30% • 80% of colorectal cancers arise in persons with no known risk factors • Most carcinomas arise from polyps but the vast majority of polyps do not become carcinomas • There is a direct relationship polyp size and its propensity to become malignant

  26. CTC discussion • Conventional endoscopy regarded as the “gold standard” against which all other procedures are compared • There are substantial variations in the scientific literature in estimates of CTC accuracy • 10% of polyps greater than 1 cm become malignant in ten years • Polyp size has a great influence on detection sensitivity From Table 1.

  27. Procedure Risks • Large intestine wall perforation may occur during CTC, barium enema, fiberoptic colonoscopy • The risks for CTC perforation (<1/2000) are higher than the rate quoted for barium enemas and lower than that for conventional colonoscocpy • 40% of patients have CTC abnormalities which may be of no clinical interest • CTC positive findings • Polyps found should be removed

  28. Radiation Dose Table 3.

  29. CTC Conclusions • Cancer risk low compared to spontaneous incidence • As CTC screening increases the number of extra cancers from the procedure may also increase • Proposed CTC screening interval is five years • Implementation of low dose techniques are likely • A number of authors have developed innovative colonic phantoms to optimize CTC protocols • Ultra-low dose protocols result in an effective dose of 1-2 mSv (even 0.05 mSv shown to be feasible!) with polyp detection sensitivity of over 80% for polyps greater than 5mm • Low dose options optimize the procedure, reduces risk and perhaps justifies routine use of CTC

  30. In conclusion …

  31. The dilemma • The dilemma expressed to some degree in all three reports. • When sophisticated but expensive equipment is available there are inevitable pressures to expand applications • New technologies associated with computed tomography are changing rapidly with time, providing improved images and, possibly, better diagnoses of disease BUT due to radiation dose, different considerations need to apply to symptomatic and to asymptomatic patients.

  32. In conclusion • IAEA Safety Report Series No. 58 , No. 60, No. 61 are a nice compact introduction to the primary and basic challenges with patient and occupational radiation exposure from PET/CT and CT procedures. • They are reports to keep in your pocket but technologic advances leave a few questions unanswered. • Being one step behind may be the perpetual dilemma of all comprehensive reports • We are still in the wild west …

  33. Thank you …

  34. References • 1) Brenner D. J., Hall E. J. Computed tomography—an increasing source of radiation exposure. N. Engl. J. Med (2007) 357:2277–2284.[ • 2) Broder J., Fordham L. A., Warshauer D. M. Increasing utilization of computed tomography in the pediatric emergency department, 2000–2006. Emerg. Radiol (2007) 14:227–232 • 3) Bedetti et al., Cumulative patient effective dose in Cardiology, Br Inst Radiology 81 (2008),699-705

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