A recent chain email, forwarded by a friend, has me concerned. The email focuses on a recent episode of “The Dr. Oz Show,” in which Dr. Mehmet Oz suggested that radiation from mammograms and dental X-rays could be partly responsible for increasing rates of thyroid cancer. According to the email, thyroid guards are available to protect patients during dental and breast imaging, but are not routinely used. My questions: How serious are these thyroid risks? Should I insist on using a thyroid guard when I have dental X-rays and mammograms?