Answer to Question #2992 Submitted to "Ask the Experts"

The question as to whether the use of lead or drywall provides adequate shielding for a chiropractic x-ray unit is impossible to answer without additional information. Guidance on shielding evaluations of diagnostic x-ray facilities can be found in the National Council on Radiation Protection and Measurements (NCRP) Report 49, "Structural Shielding Design and Evaluation for Medical Use of X Rays and Gamma Rays of Energies up to 10 MeV (1976)."  To properly evaluate shielding requirements, the following factors need to be considered.

1. EXPOSURE LIMIT TO PEOPLE OUTSIDE OF THE RADIOGRAPHIC ROOM: By regulations, exposures to occupational or radiation workers are to be kept to 50 millisievert (mSv) or 5,000 millirem per year. By medical staff, I assume that not all of the individuals who could be exposed are radiation workers. In this case, what limit is going to be used? NCRP Report 49 recommends a limit of 5 mSv per year for nonradiation workers, but many state regulations require their exposures to be limited to 1 mSv per year.
    
2. WORKLOAD OF THE RADIOGRAPHIC UNIT: How many x rays will be taken in a week and of what type? What are the typical techniques used for each type of exam? That is, what are the time, current, and kilovoltage settings for a typical lumbar spine exam, a knee exam, a cervical spine exam, etc. This information is necessary for calculations of exposures along the direction of the primary radiation beam and for leakage and scatter radiation shielding calculations out of the primary beam.
    
3. ORIENTATION OF THE PRIMARY X-RAY BEAM: What percentage of the exams will the primary beam be aimed in a particular exam? Will 40 percent of the exams, for example, require the primary beam to be aimed toward the floor? During cross-table exams, will the primary beam be aimed toward an exterior wall, an office, a corridor, etc.?
    
4. UTILIZATION OF ADJACENT AREAS AROUND THE X-RAY FACILITY: As part of the evaluation, how frequent are the areas adjacent to the x-ray facility occupied by people? The chance that a person will be in a corridor during x-ray examinations is less than at an office that is occupied all of the time.

My recommendation is to consult with a health or medical physicist who has experience in evaluating radiation shielding requirements. Qualified individuals are usually registered with the radiation regulatory agency in the area where you live. If you are in the United States, a list of state radiation regulatory agencies can be found at the Conference of Radiation Control Program Directors' Web site.

Finally, with regard to your question if x rays travel only in a "horizontal" direction or if they can radiate around or over a wall, photons behave as visible light does. It can be scattered off of objects or refracted or "bent" off of its initial direction as it passes through matter. However, in the process, the intensity of the scattered radiation is reduced by significant amounts.

John Jacobus, MS
Certified Health Physicist