(Wednesday, 7/17/2019) 10:30 AM - 11:00 AM
Room: Exhibit Hall | Forum 9
Purpose: Perfusion studies deliver one of the highest exposure doses among clinical CT head protocols. The purpose of this study is to investigate the eye lens dose accumulated from Shuttle-mode perfusion CT exams, and the effect of Organ Dose Modulation (ODM) on the dose to the lens of the eye.
Methods: For this study a skull phantom and OSL dosimeters (NanoDots) were implemented to measure eyes dose. Scans were performed with a GE - OPTIMA CT660 scanner. The calibrated dosimeters were placed on the eyes of a skull phantom. The phantom was scanned using AAPM shuttle-mode protocol with a CTDI of 174 mGy. Neither gantry tilt nor ODM were allowed for this mode. Scans with the phantom tilted (chin tucked) were also performed. Since the protocol did also include an axial head scan (CTDI= 56 mGy), other NanoDots (calibrated for 120 kV) were used.
Results: From the NanoDot results, the eye lens dose from the shuttle-mode CT perfusion (CTP) was estimated to be 153.3 mGy. The axial fixed mAs CT scans were compared with the eye dose from the same CT scans acquired with ODM. No significant difference in eye dose was found between axial scans with fixed mAs and ODM. Both scans resulted in 0.91 per mGy CTDI. Perfusion scans with the phantom head tilted to lower the dose to the eyes lens showed reduction of about 80%.
Conclusion: In helical shuttle CTP, dose to the eye lens reaches 0.88 per mGy CTDI. Since the ODM and gantry tilt are not applicable in this mode, applying chin tilt may reduce a dose up to 80%. Further investigations will be performed and presented on effectiveness of both ODM on axial scans and chin tilt angle in shuttle CTP.
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