IS THERE A RATIONAL APPROACH TO RADIATION RISK? Philip F. Judy Ph.D. Department of Radiology Brigham and Women's Hospital New England AAPM Chapter Meeting February 15, 2008

Invitation from Robert Cormack “One subject that is of interest to the group is the safety of low diagnostic levels of radiation especially after the recent paper in NEJM. Lee Chin mentioned that you would be well suited to speak about this issue, and I've always appreciated your viewpoint in the BWH RSC meetings.”

Phil Judy response: Many in this audience are more qualified to speak. Whether I am well suited, time will tell. Robert may not completely appreciate the basis for my “viewpoint” at BWH Radiation Safety Committee meetings.

My comment at a 1974 PPBH Radiation Safety Committee Meeting Informed consent for a radiation study requires the statement that the radiation exposure will result in an increased risk of cancer. Without such a statement the consent is not informed. The committee’s response has been no way can such a statement could be included in the informed consent, because there will be no volunteers for research protocols involving radiation exposure.

2008 Risk statement from a consent form – No real change from 1974 “A portion of this study will involve exposure to radiation for research purposes. The radioactive drug study proposed will expose you to 0.7 rem (a rem is a unit of radiation dose). This is equivalent to 14 % of the 5 rem annual limit for a person who works with radiation, or 3 times the natural environmental radiation the average person receives in the United States annually.”

Basis for my position Statement by Eric Hall in his textbook: Radiobiology for the Radiologist – page 145. “The belief that stochastic effects have no dose threshold is based on the molecular mechanisms involved. There is no reason to believe that even a single x-ray photon could not result in a base change leading to a mutation that could cause cancer or a hereditary defect.”

Computed Tomography An Increasing Source of Radiation Exposure David J. Brenner, Ph.D., D.Sc., and Eric J. Hall, D.Phil., D.Sc. New England Journal of Medicine 2007;357:

Brenner and Hall, NEJM, 2007 “In summary, there is direct evidence from epidemiologic studies that the organ doses corresponding to a common CT study (two or three scans, resulting in a dose in the range of 30 to 90 mSv) result in an increased risk of cancer. The evidence is reasonably convincing for adults and very convincing for children.”

Do you believe that radiation exposure from a CT exam increases an individual’s risk of cancer? Respond now!

Brenner and Hall, NEJM, 2007 “In a recent survey of radiologists and emergency-room physicians … 53% of radiologists and 91% of emergency-room physicians did not believe that CT scans increased the lifetime risk of cancer.”

Why change in Eric Hall’s argument from molecular mechanism to direct evidence? Radiation exposure from CT exams is considerable large than projection radiographs. Multi-detector CT has lead to several scans becoming part of standard CT exams. CT exams are repeated. Radiation exposures have increased so direct evidence applies!

Some evidence that radiation exposure from CT exams is considerable larger than projection radiographs.

Dose - Typical Exams BWH Abdomen/Pelvis Exams RadiographicESD (mGy)Eff. Dose (mGy) Single film CTCTDI (mGy)Eff. Dose (mGy) Single scan Nawfel RD, Judy PF, Schleipman AR, Silverman SG. “Patient radiation dose at CT urography and conventional urography,” Radiology 2004 Jul;232(1):126-32

Risk of Radiographic Examinations of Chest Judy PF. “Multidetector-row CT image quality and radiation dose: imaging the lung,” Semin Roentgenol 2003 Apr;38(2):

Diagnostic Procedure Typical Effective Dose (mSv) Number of Chest X rays (PA film) Time Period -Natural Background Radiation Chest x ray (PA film ) days Skull x ray days Lumbar spine days I.V. urogram days Upper G.I. exam year Barium enema years CT head days CT abdomen years

Image Quality Measurement & Prediction Risk & Benefi t Patient Radiation Dose

Risk and Benefit Estimate radiation risk and benefit from CT protocols –Determine characteristics of cases (e.g., age, sex, purpose of exam, and exam frequency) –From effective dose calculate excess mortality associated with radiation exposure (individual and population) –Determine benefits and non-radiations risks of the outcomes of the imaging exam.

Purpose of human radiation exposure (case classification) Research - no benefit to individual – other individuals in future may get benefit Screening – individual may get benefit but typically others will get benefit Diagnosis – benefit to individual Cancer staging and treatment evaluation – benefit to individual Image guided treatment – benefit to individual Combinations of above – usually clinical trials