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Validation of Ceiling Shielding in CT/PET Room with RADEYE

L Ding

L Ding*, G Nguyen, T Yoshizumi, Duke University Medical Center, Durham, NC

SU-C-144-3 Sunday 1:00PM - 1:55PM Room: 144

Purpose: The purpose of this study was two-fold: (a) to measure the magnitude of scattered radiation levels in CT/PET room; and (b) to evaluate the effectiveness of shielding of the ceiling of a PET/CT suite.

Methods: Six RadEye detectors were placed in the CT/PET room, four in the ceiling, and two at one meter above floor. A RadEye detector recorded data every 25 seconds throughout the day. The detector was turned on at the beginning of the day and the doses were transferred to a laptop for analysis at the end of the day. The dose to a non-radiation worker above the CT/PET room was estimated based on the ceiling data. The dose build up factor was used in the dose estimate. The magnitude of transmitted CT radiation in the room above was measured separately with RadEye.

Results: The CT component of the scattered radiations showed approximately cone beam shape of the iso-dose curve. The CT dose contributed about 80% of the total dose while the PET contributed 20% within the scanning room. The combined dose to a person upstairs sitting in a chair at 0.5 meter high above the PET/CT suite was 4x10-6 mSv per week. In addition, the physical measurement at the interstitial space above the ceiling recorded only 0.12 mR per day, which was the background dose.

Conclusion: This study has quantified the CT and PET doses contributions separately in the clinical CT/PET room. An analytical model was developed to calculate the non-occupational personnel dose above the CT/PET room and the calculated results were confirmed by physical measurements. The actual physical dose was 50 times smaller than the NCRP design goals of 0.02 mSv/wk.

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