Shielding from radiation

Richard Whittington, MD
Last Modified: September 15, 2002


Dear OncoLink "Ask The Experts,"

Why doesn't conformal radiation therapy for prostate cancer include coverage of the rest of the body with a protective lead shield to protect from x-ray exposure? You get zapped at the dentist's office and wear a vest, why not with conformal radiation therapy?



Richard Whittington, MD, Associate Professor of Radiation Oncology at the University of Pennsylvania School of Medicine, responds:

Patients receiving conformal radiation therapy are shielded. The shielding is in the head of the machine. The dentist's office is a smaller room and the machine has to be lighter and portable to move around the patient. The radiation machine head weighs over a ton because of the lead and depleted uranium shielding in the head of the machine. To put a ton of shielding on the patient would crush them. It is like treating a patient through a wall with a hole in it. It is easier for the machine with its motors and steel frame to bear the weight of the wall than it is for the patient. Much thinner shields can stop dental x-rays. 1/2 millimeter of lead absorbs more than 90% of the radiation. 12 millimeters of lead will absorb 50% of what comes out of a radiation therapy unit.