Title: Evaluation of Shielding for PET/CT Category: Radiation Protection
Date Initiated: December 15, 2005
Date Completed: September 30, 2006
A) Significance:
We are installing a new PET/CT for which I did the shielding design. Prior to use, we need to evaluate the shielding so we can show that the annual exposure is less than 1 mGy per year in uncontrolled areas and less than 5 mGy per year in controlled areas. State regulations would allow up to 50 mGy per year in controlled areas, but for reasons of ALARA, we have decided to use 5 mGy.
This SDEP will involve:
• Determining the best instruments to use
• Developing efficient techniques for testing to save time and reduce radiation dose to the evaluators
• Developing a spreadsheet to collect and analyze the data
B) Approach/Resources Utilized:
• Complete a literature review using PubMed and Google.
References will include AAPM Task Group Report on PET shielding.
• Derive appropriate equations for evaluating the shielding.
• Determine the most appropriate test equipment.
• Determine best strategy to insure that radiation exposure to physicists conducting the test remains ALARA.
• Make appropriate measurements.
• Report results.
Key Literature
• Patient self-attenuation and technologist. Zeff Yester
MedPhys 32:861-865, 2005.
• AAPM Task Group Report 108: PET Shielding.Med Phys 33;4-
15, 2006.
• Photon Shielding for a PET Suite. Health Physics 81;S24-
28;2001.
We have three possible instruments for evaluating the shielding: an Inovision 451 P pressurized ionization chamber, a Radcal 1010 with a large volume ionization chamber, and an Exploranium. We will determine the best equipment for testing and develop a spreadsheet.
C) Evaluation/Documentation of Achievement:
a. Prospective Statement:
• Conduct measurements to determine the most appropriate equipment.
• Derive equations for efficient testing.
• Create a spreadsheet to implement the equations.
• Test the shielding at the PET facility under construction.
• Present the results at a meeting.
b. Final Statement:
• The instruments were tested. They were all acceptable, but the
Exploranium was the most convenient.
• Presented two talks on PET test: National AAPM 2006 and
World Congress of Medical Physics 2006.
• Derived the appropriate equations and spreadsheet.
• The shielding was tested on 1/11/2006.
D) Impact on Practice/Outcome Statement:
a. Prospective Statement:
It is expected that the testing will be efficient. The testing will be done appropriately and can serve as a resource for the community.
b. Final Statement:
Testing was done efficiently. The talk from AAPM 2006 is in the virtual library, so it is available for other physicists.