Last month we discussed the issue of the hospital in Aurora, CO that reportedly removed the requirement for shielding patients of any age, from babies in NICU to pregnant women. The ensuing controversy has been vigorously debated and led us to consult our expert, Lou Wagner, PhD.
We quoted a part of his response in the last blog and will continue with his words of wisdom below as Dr Lou speaks:
“Many personnel perceive radiation exposure in a room as something like an imperceptible gas that permeates the room from all directions. This is not so and an understanding of radiation distribution in the room is important but poorly perceived by many personnel.
X rays travel in a straight line at the speed of light unless they interact with something. X-ray radiation in medicine is generated inside a box that is well-shielded to assure radiation escapes the box only through a portal directed at the patient (yes, this is a generalization, and there is some escape through the walls of the box. Those levels of escaped x rays are too low for serious consideration in this e-mail). The x-ray beam is comprised of a plethora (think billions and trillions) of individual particles we call photons. They all are traveling toward the patient when they escape the box through the portal. Many will be absorbed inside the patient’s body and cease to exist. A small percentage (think a few percent for our purposes) completely penetrate the patient to reach the detector where the image is produced. Others will collide with atoms or molecules in the patient and be deflected at a degraded energy in some other direction. These x rays are the scattered or stray x rays that principally expose personnel in the room. So, IT IS IMPORTANT TO UNDERSTAND THAT THE PRINCIPAL SOURCE OF RADIATION EXPOSURE TO PERSONNEL EMANATES FROM AND AWAY FROM THE PATIENT. It is best just to let them escape into the room.
The overall consequence is that we cannot shield the patient from x rays originating from inside them because those x rays travel out and away from the patient. Some of the scattered x rays travel internally inside the patient either in a superior or inferior direction. The x rays that travel internally within the patient cannot be blocked either, for obvious reasons. Further, the x-rays that escape into the room generally just disappear from the environment because they are absorbed in the walls. The level that might be reflected back into the room is piteously small and further degraded in energy.
Many personnel use the logic that if we require shielding be worn by personnel we should also require the patient be shielded. My explanation above demonstrates that this logic is falsely applied. Personnel can be shielded from radiation that emanates from the patient, but the patient physically cannot be shielded from radiation that emanates from the patient for the patient physically cannot be shielded from radiation that emanates from the patient.
Many personnel do not understand that the radiation machine is smart and adjusts radiation output to suit the size of the patient. If the shielding accidently or by intention gets into the main beam, the machine will increase output to penetrate the shield. The shield does not effectively reduce radiation exposure because the output is simply increased to assure penetration through the shield. I recently had a physician who thought that wrapping a pregnant patient in a lead apron from chest to pelvis would protect her from radiation from a procedure performed in the abdomen. In other words, the protective apron was twice in the beam at all times – posteriorly and anteriorly. Such egregious misunderstanding of how radiation is generated and how to protect people from unnecessary levels is unforgiveable.
People by nature seldom observe what they cannot see. ___ I know that sounds weird, but it is true. Personnel like the lead apron because they can see it and think it is helpful because it is there. They do not understand the nuances of its proper application and do not perceive that its value is severely limited. On the other hand they do not see the protection provided by the machine itself. There are many protective devices in the machine that are far better at protecting the patient than any lead apron”
Be sure to join us for the next installment and hear the answers to many of the questions our readers wanted to ask Dr Lou.
