|
|
Application of the IEC3.1 standard of CTDI100 to a supine CBCT device Host Publication: Abstract book of European Congress of Radiology (ECR 2019) Authors: B. Keelson, D. Buytaert, G. Van Gompel, J. Casselman, K. Bacher, Y. De Brucker and N. Buls Publication Year: 2019
Abstract: Purpose: To investigate the feasibility of extending the IEC 3.1 CTDI100 asdefined by the IAEA to CBCT and compare with device indicated CTDI and anapproximation of the "true" CTDI.Methods and Materials: Weighted CTDI (CTDIw) measurements of a 16cmdiameter dosimetry phantom were obtained on a Newtom 5G (Newtom,Verona, Italy) CBCT using a 15x5 cm and 15x12 cm field-of-view (indicated asdiameter by height).CTDIw following the IEC 3.1 definition was computed bymultiplying the CTDIw of a reference collimation (15x5) with the quotient offree-in-air CTDI measurements at the collimation of interest (15x12) and thereference collimation. In addition, to approximate CTDI8 ("true" CTDI), CTDI measurements were performed in a 32 cm long phantom, constructed as alongitudinal combination of two 16 cm diameter phantoms. For the lattermeasurements, referred to as CTDI300, an integration length of 30 cm wasused i.e. integrated dose over three adjacent positions with the pencilchamber.Results: True CTDIw values were 22mGy/100mAs and 25,8mGy/100mAs forthe 15X5 and 15X12 protocols respectively. These values corresponded to anunderestimation by the device Indicated CTDIw values of 57% and 31% for the15x12 and 15 x 5 protocols respectively. The IEC 3.1 definition howeverresulted in underestimations of 18 and 14 % for the 15x12 and 15x5 protocolsrespectively relative to the true CTDIw.Conclusion: CTDI using the IEC 3.1 method resulted in reasonable deviationsfrom the "true" CTDI and is recommended to allow for comparison of dosesbetween conventional CT and CBCT.
|
|
