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Measurement of Imaging Dose Outside CBCT Scan Length

S Deshpande*, V Kannan , S Naidu , P.D.Hinduja National Hospital Mumbai, Mumbai, MH


(Sunday, 7/14/2019) 3:00 PM - 3:30 PM

Room: Exhibit Hall | Forum 9

Purpose: To measure imaging dose outside scan length from Kilo voltage cone beam computed tomography (kV-CBCT) and its clinical application.

Methods: To measure imaging dose outside the field edge from kV-CBCT TLD chips were arranged along y direction at one centimeter apart. Total 10 TLD chips were placed from edge of the field, they were placed one centimeter apart so as to measure dose up to 10 centimeter from field edge. We measured dose outside field at the depth of 8 cm. We used standard dose head and neck CBCT protocol (kVp 100V and mAs 145). We performed these measurements on Varian clinic IX machine. To get sufficient signal TLD chips were irradiated for five times with same setup.

Results: Imaging dose fall off outside scan length very rapidly. It has observed that dose at one centimeter is 48.4 % of central axis dose, 17.8 % at 5 centimeters and 5.8 % at 10 centimeter from central axis.

Conclusion: While performing CBCTs the organ at risk can be kept outside the scan area by carefully setting the scan length to irradiate only the area of interest. Clinically this can be applied while imaging the head and neck cases where eye lens is a very radiation sensitive structure. Even a simple technique of maintaining a 1cm distance between field edge and eye lens can reduce the imaging dose to eye lens by nearly 50%.


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