Diagnostic Radiation Shielding Considerations

Per the current NCRP Report #147(2004)1.5 General Concepts, states: "The term "qualified expert" used in this report is defined as a medical physicist or medical health physicist who is competent to design radiation shielding for medical x-ray imaging facilities. The qualified expert is a person who is certified by the American Board of Radiology, American Board of Health Physics, or the Canadian College of Physicists in Medicine."

Radiation shielding shall be designed by a qualified expert to ensure the required degree of protection is achieved.

"The qualified expert should be consulted during the early planning stages since the shielding requirements may affect the choice of location of radiation facilities and type of building construction. The qualified expert should be provided with all pertinent information regarding the proposed radiation equipment and its use, type of building construction, and occupancy of nearby areas. It may be necessary to submit the final shielding drawings and specifications to pertinent regulatory agencies for review prior to construction".

Lead shielding requirements should be calculated and determined by a certified radiation health physicist based on the following factors:

  1. Energy: How powerful is the x-ray unit(s) output in kVp? Typically, the higher the output, the higher the shielding requirement.
  2. Workload: How many exposures per week / month / year? Maximum patient volume growth should be projected in, as radiation is cumulative and overexposure causes biological damage on the cellular level. As an example, in California, it is limited to a maximum permissible exposure level of 100 millirem per year, in addition to the 360 millirem of radiation the average person is exposed to per year due to environmental factors (i.e.: ultra violet, solar, radon gas and atmospheric radiation). Always check with all local health and safety laws and codes for current compliance requirements.
  3. Orientation: Each wall section will be calculated by your physicist in relation to the direction of the primary beam target (where it will be aimed) and scatter (secondary) radiation of the x-ray unit, as well as floor or wall bucky cassette holder (target area).
  4. Distance: Radiation dissipates as distance increases. Typically, the closer a partition is to the radiation / x-ray source, the higher the lead shielding requirement.
  5. Occupancy: One of the most important factors of calculation is how much time in a day that a surrounding room common to the x-ray room will be occupied by your personnel or the public. (i.e.: a storage room would have a lower occupancy factor and a waiting room or office may be high). Therefore, it is calculated room by room for all rooms connected (or common) to the x-ray room. If there is no occupancy potential, then typically no shielding will be required (i.e.: floor or roof of a single story building).
  6. Material: Sometimes a physicist will take into consideration the existing or proposed construction material of the wall partition or flooring material, as heavy density materials can attenuate (shield) radiation to a certain degree, such as concrete, steel, plaster, block or multiple layers of drywall. This may reduce, or in some cases, eliminate your lead shielding requirements, depending on the values of the previous five factors to be considered. Always select high quality shielding materials and products by only purchasing from experienced, knowledgeable suppliers with an established good reputation such as Ray-Bar Engineering Corporation at 1(800)444-XRAY
  • There may also be other considerations, such as x-ray film to be protected from radiation exposure to prevent "fogging" and the shielding of various radiation sensitive equipment, or designations of perimeter occupancies as "controlled" or "uncontrolled."

Important notes:

  • All penetrations within a shielded wall partition must be properly shielded with lead or other material of equal or greater thickness.
  • Minimum height of wall shielding is 7'0" A.F.F. per NCRP Report #49 (national standard)
  • Lead shielding for partitions must be bonded to rigid panels (i.e.: drywall, plywood, or paneling) for structural strength.
  • Shielding requirements may change if any one of the five basic factors change.
  • All radiation producing sources must be licensed and registered.
  • Typical diagnostic rooms: X-Ray, Radiographic, Fluoroscopic, C.T. Scan, Cath Lab, Angiography, Cat Scan, Pet Scan, Mammography, etc.
  • Radiation therapy room calculations are much more involved than diagnostic shielding due to the much higher radiation energy levels and other important considerations that arrise with these room types.
  • End user should always have all completed projects tested and surveyed by a qualified radiation health physicist after installation and prior to any occupancy or use.

Please contact Ray-Bar directly for additional technical assistance in designing and providing the x-ray protective materials and radiation shielding products your room needs: Phone# 1(800)444-XRAY(9729) or e-mail at sales@raybar.com or go to our contact us page on this website.

"When protection is required, there is no substitute for skill and experience"

TERMS

Activation
The process of making a radioisotope by bombarding a stable element with neutrons, protons, or other types of radiation
Alpha particle
A positively charged particle ejected spontaneously from the nuclei of some radioactive elements with very low penetrating power and a short range. Alpha particle will generally be easily stopped by a sheet of paper.
Atom
The smallest particle of an element that cannot be divided or broken up by chemical means consisting of a central core of protons and neutrons, called the nucleus, with electrons revolving in orbits surrounding the nucleus.
Attenuation
Attenuation is the process by which the number of particles or photons entering a body of matter is reduced by absorption and scattering.
Background radiation
Radiation from cosmic sources; naturally occurring radioactive materials, including radon (except as a decay product of source or special nuclear material), and global fallout as it exists in the environment from the testing of nuclear explosive devices. The average individual exposure from background radiation is approximately 360 millirems per year.
Becquerel (Bq)
The unit of radioactive decay equal to one disintegration per second. The Becquerel is the basic unit of radioactivity used in the international system of radiation units, referred to as the “SI” units. 37 billion becquerels = 1 curie (Ci).
Beta particle
A charged particle emitted from a nucleus during radioactive decay, with a mass equal to 1/1837 of a proton. Thin sheets of metal or plastic may stop beta particles.
Curie (Ci)
The original unit used to express the decay rate of a sample of radioactive material. . It was based on the rate of decay of atoms within one gram of radium. It is named for Marie and Pierre Curie who discovered radium in 1898. The curie is the basic unit of radioactivity used in the system of radiation units in the United States, referred to as "traditional" units.
Detector
A material or device that is sensitive to radiation and utilized for measurement or analysis. A radiation detection instrument.
Dose
A general term used to refer to the effect on a material that is exposed to radiation. It is used to refer either to the amount of energy absorbed by a material exposed to radiation or to the potential biological effect in tissue exposed to radiation
Dosimeter
A small portable instrument (such as a film badge, thermoluminescent or pocket dosimeter) for measuring and recording the total accumulated dose of ionizing radiation.
Dosimetry
The theory and application of the principles involved in the measurement of ionizing radiation doses.
Electron
A negatively charged beta particle.
Exposure
A general term used loosely to express what a person receives as a result of being exposed to ionizing radiation.
Film badge
Photographic film used for measurement of ionizing radiation exposure for personnel monitoring purposes
Gamma radiation
High-energy, short wavelength, electromagnetic radiation emitted from the nucleus of an atom. Gamma radiation frequently accompanies the emission of alpha and beta particles
Geiger-Mueller Counter
A radiation detection and measuring instrument. It is also called simply a Geiger counter or a G-M counter, and is the most commonly used portable radiation measuring instrument.
Half-life
The time in which one-half of the activity of a particular radioactive substance is lost due to radioactive decay.
Health Physics
The science concerned with the recognition, evaluation, and control of health hazards to permit the safe use and application of ionizing radiation.
Mrem (Millirem)
One thousandth of a rem.
NCRP
The National Council on Radiation Protection and Measurements
Neutron
An uncharged elementary particle with a mass slightly greater than that of the proton, and found in the nucleus of every atom heavier than hydrogen.
NORM
An acronym for Naturally Occurring Radioactive Material. Naturally occurring radioactive materials are common in virtually all rocks, minerals, and soils. They naturally contain small amounts radioactive isotopes. Plants and animals are also naturally radioactive; they contain very small levels of radioactive materials that are formed by cosmic ray interactions in the atmosphere.
Photon
A quantum (or packet) of energy emitted in the form of electromagnetic radiation. Gamma rays and x rays are examples of photons.
Positron
A positively charged beta particle
Rad
The original unit developed for expressing absorbed dose, which is the amount of energy from any type of ionizing radiation such as alpha, beta, gamma, x-rays, neutrons, etc. A dose of one rad is equivalent to the absorption of 100 ergs (a small but measurable amount of energy) per gram of absorbing tissue. The rad has been replaced by the gray in the SI system of units (1 gray = 100 rad).
Radiation area
Any area with radiation levels greater than 5 millirems in one hour at 30 centimeters from the source.
Radiation (diagnostic)
Alpha, Beta, Gamma, X-Ray, Protons, Neutron and other energy given off as either particles or rays from the unstable nucleus of an atom
Radioisotope
An unstable isotope of an element that decays or disintegrates spontaneously, emitting radiation. Approximately 5,000 natural and artificial radioisotopes have been identified.
Radiological survey
The evaluation of the radiation hazards under a specific set of conditions. Such evaluation customarily includes a physical survey of materials and equipment, measurements or estimates of the levels of radiation that may be involved
Radiology
The medical diagnostic imaging and therapeutic treatment applications of radiant energy, including x rays and radioisotopes.
Rem (Roentgen)
A unit in the traditional system of units that measures the effects of ionizing radiation on humans.
Scatter radiation
Radiation that, during its passage through a substance, has been changed in direction. It may also have been modified by a decrease in energy. It is a form of secondary "scatter" radiation.
Sievert (Sv)
The international system (SI) unit for dose equivalent equal to 1 Joule/kilogram. The sievert has replaced the rem. One sievert is equivalent to 100 rem.
Shielding
Any material, product or other obstruction that absorbs radiation and thus tends to reduce or protect personnel, equipment or materials from the effects of ionizing radiation.
X-Rays
Penetrating radiation having a range of wavelengths (energies) that are similar to those of gamma photons. X-Rays are usually produced by excitation of the electron field around certain nuclei.