Monday, March 24, 2008

Concerned About Scatter Radiation???

Concerned by the recent information from ISI on the levels of scatter radiation produced by the i-Cat, I contacted a friend of mine who is a radiation physicist and asked if my layout was safe. This is the response I received.

"Based on the info attached for the scatter measurements (20 second scan measured at 3, 6 & 9 feet from the source of scatter), as long as you stand 9 feet away, you can do up to 50 scans/week without any additional shielding and still be at the exposure level for public occupancy (100 mR/year), much less controlled occupancy."

I feel a lot less concerned now.


Blogger devery said...

I stand behind a 5/8 sheetrock wall and look through leaded window. Feel pretty safe

10:03 PM  
Blogger Eric Iwamoto said...

Los Angeles County ordinance 11.22.620 states that shielding designs for radiation safety must be approved by the Department of Health Services (DHS), County of Los Angeles, Radiation Management Department for all x-ray rooms.

I thought you might be interested when my office submitted an application for the i-CAT back in 2004. Having the second i-CAT machine (Don Croall has the honor of being first) installed in a new x-ray room required the radiation shielding plan application that was submitted as follows:

1. Radiation Shielding Plan
2. Diagram of x-ray room
3. Diagram Key
- Specifications of dental
x-ray laboratory
-Technical specifications
from ISI regarding i-CAT
4. Dosimeter report for i-CAT
5. Renewal of radiation machine
- (required upon possession
of additional radiation
6. Facility inspection report
(inspected and measured
radiation levels)
7. Personnel Exposure records
check of film badges by Los
Angeles County Department
of Health Services, Radiation

The Bureau of Environmental Protection, Radiation Management Department performed an evaluation on my proposed x-ray room addition and made recommendations to reduce the radiation exposure to as low as reasonably achievable by adding lead shielding to the floor (my office is located on the second floor of a two story building) and walls. Windows, window frames, doors and door frames shall have the same lead equivalent as that required of the adjacent wall.

DHS states the time periods (occupancy factors in percentage of time) used for calculation purposes for any one individual to be in an area relative to the x-ray room are 100 percent, except as noted below:

Area Time *
Waiting Room 25%
Room Entrance 25%
Hallway 25%
Roof 6.25%

*Percentage of time an individual would be in this area. (Isn’t it interesting they feel someone would be on the roof 6.25% of the time?)

After the i-CAT was installed and operational, my facility was inspected because it was the first Los Angeles recorded radiation shielding application of a cone beam unit in a new x-ray room. The radiation management team was initially concerned about the radiation levels. After extensive on-site testing revealed scatter levels equivalent to a panoramic unit, they were satisfied that the i-CAT was operating well within regulations.

However, my application triggered a red flag at the Department of Health Services (DHS), Radiological Health Branch in Sacramento and they decided that the State of California should immediate test one of these new cone beam units. DHS discovered that DDI had a NewTom cone beam right in their backyard in Sacramento. According to Craig Dial, DHS visited DDI and strategically placed highly sensitive dosimeters all around the x-ray room and they even put one right on top of the cone beam unit! The results confirmed the Los Angeles testing performed at my office and verified the new cone beam units were emitting scatter radiation levels closer to a panoramic than medical CT
(which I presumed was their main concern).

As noted above, our personnel film badge reports have indicated that the recorded exposure levels are still at a minimum, even after the i-CAT installation. It is a always a good idea to provide your entire staff with personnel film badges to have an official record of the minimal exposure.

12:51 PM  
Blogger Matt Kroona said...

Eric, it's trail blazers like you and Don and Craig that help make the road easier for folks like me.

2:26 PM  
Blogger Eric Iwamoto said...

Thank you Matt, your appreciation is most welcome!

5:39 PM  

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