Evaluation of normal organ doses for extended kV- CBCT protocol in para-aortic region treatment using nanoDot dosimeter

Abstract

Extended cone beam computed tomography (CBCT) imaging protocol was used to extend the longitudinal coverage by acquiring double CBCT which allows an overlapping of doubled doses from the two orbits. The aim of this study was to evaluate the absorbed doses of three normal organs; bladder, small bowel, and rectum in the overlapped region for extended CBCT imaging protocol with 125 kV and 592 mAs of Ethos™ machine in para-aortic lymph node treatment using nanoDot™ dosimeters placed on the Rando phantom. The nanoDot™ correction factor (CFOSLD) and an organ depth dose correction factor (CFDepth) were used to calculate the absorbed doses of each organ. The result showed that the absorbed dose for bladder, small bowel and rectum were 18.71 ± 0.99, 19.57 ± 0.05 and 20.93 ± 0.74 mGy, respectively, which are lower than the radiation tolerance doses. However, the overlapping dose from the extended CBCT protocol should be considered to estimate the imaging dose throughout the treatment course for managing the use of extended CBCT to verify patient positioning before treatment. Additionally, the results can be used to determine the radiation dose in treatment planning to keep the additional imaging dose to the patient as low as reasonably achievable.