Medical Physics Seminar – Monday, October 24, 2011
Radiation Safety in Medical Imaging
Frank Ranallo, Ph.D., DABR
Associate Professor(CHS), Medical Physics and Radiology, UW-School of Medicine & Public Health, Madison, WI USA
The actual and possible detrimental effects of radiation from medical imaging have been frequently in the news over the last few years. Most of this discussion has centered on computed tomography and its increasing use in medical diagnosis. This has resulted in beneficial discussions on how we can reduce unnecessary radiation, but has also resulted in unfounded fears in many concerning the radiation from medical imaging and the resultant avoidance of needed imaging procedures.
This talk will provide information on the basics of radiation and its possible clinical effects. It will cover the following topics:
• Radiation Units
• Typical radiation exposures from background radiation and other sources including medical procedures
• The clinical effects of radiation:
o Deterministic
o Stochastic, including arguments concerning the validity of the Linear No-Threshold Hypothesis
o Effects on the conceptus
• Exposure Limits for occupational exposures and exposures to the general public
• Minimizing radiation dose to the clinician and patient in medical imaging procedures
While it is important in medical imaging to avoid unnecessary radiation exposure to the patient, it is even more important to provide adequate clinical image quality for proper diagnosis. The radiation dose should never be lowered to the point that important diagnostic information is compromised.
As one example: The clinical guidelines of the ACR either recommend (adult) or require (pediatric), that routine head scans not include the eyes in the image. This appears to be based on a desire to prevent the formation of cataracts in the patient. However some important diagnostic information may be missed by limiting the imaging in this way. There appears no logical reason for not imaging the eyes since the formation of cataracts is presently believed to be a threshold phenomenon, whose threshold dose is about one thousand times the amount of radiation the eyes of patient would receive in a CT scan.