CBCT System Radiation Shielding in Dental Practices
Considerations when Replacing Panoramic Systems
The use of cone beam computed tomography (CBCT) systems in dental and orthodontic practices has become commonplace. Many practices find it straightforward to place the CBCT in the area formerly occupied by the panoramic system. However, care should be taken to ensure the difference in scatter radiation is accounted for in case additional area shielding is required.
Radiation Dose During Cone-Beam Computed Tomography
While a panoramic x-ray is considered to be a low radiation procedure, CBCT imaging typically results in a 7x higher radiation dose to patients. However, the radiation dose can be more than 10x higher. The actual dose differs considerably by model, with major factors including the energy level and exposure time.
Radiation scatter is also a consideration for staff, patients and others surrounding. The National Council on Radiation Protection and Measurements states that the scatter radiation differential is actually much higher with CBCT, ranging from 2-40 uGy/scan at a 1 meter distance, with the variation highly dependent on the system and imaging setup. Rather than using the highest end of this range, ask your CBCT manufacturer for specific scatter dose data.
Calculating Radiation Dose and Scatter for CBCT Procedures
Highly complex raw calculations, like those in the NCRP Report 147, can be performed by a Health Physicist to determine the amount of radiation dose and scattered delivered during a medical imaging procedure. However, simple estimates can be determined using data from the CBCT manufacturer and data from your specific layout. An example is shown below:
- Scatter Dose at 1 meter (from the manufacturer): 20 uGy/scan
- Maximum procedures performed each week in your office: 10 scans
- Distance from the CBCT to the barrier: 2 meters
- Calculate the weekly dose: 20 uGy/scan * 10 scans/wk *(1 m / 2 m)^2 = 50 uGy/wk (or 0.05 mGy/wk)
The NCRP Report 147 limits radiation exposure in controlled and uncontrolled areas. Radiation regulations and requirements can vary by country, state and territory. Local radiation experts or Health Physicists should always be consulted to insure compliance.
In a controlled area, the weekly shielding design goal is 0.1 mGy air kerma (5 mGy per annum).
In an uncontrolled area, the weekly shielding design goal is 0.02 mGy air kerma (1 mGy per annum).
In this case, a barrier used to section off an uncontrolled area frequented by non-radiation workers (administrative staff, the general public, etc) will need to provide sufficient shielding to reduce the dose equivalent by a minimum of 60% (1 - 0.02 / 0.05).
Then, determine if the current barrier would be acceptable, a reduction in radiation dose of 60% radiation would be achieved by either:
- 2 sheets of 5/8” gypsum board (drywall),
- 0.1mm of lead sheet ( or equivalent in a barrier, curtain or other shielding device)
Radiation Shielding for CBCT
Care should be taken to properly shield for the additional radiation scatter produced from CBCT procedures. Lead and lead-free radiation barriers are a highly effective way to provide a full-body shielding barrier. X-Ray room shielding in various forms is considered to be the most effective way of limiting scattered radiation.
Using leaded drywall, flexible x-ray curtains, leaded glass, mobile barriers, lead-lined doors and other shielding products are methods to shield controlled and uncontrolled areas. Many of these products can be particularly useful in dental offices.
Lead-free alternatives are available for radiation shielding, offering equal protection from scatter. Lead-free room shielding is lightweight, non-toxic and environmentally friendly.
Professional Shielding Consultation from XrayCurtains.com
As experts in design and certification of x-ray systems, we know how to provide optimized solutions for any application which will be compliant with your national regulations. The experienced staff at XrayCurtains.com can perform shielding calculations for many types of operations, whether utilizing lead or non-lead materials for shielding.