Radiation Dose from Megavoltage Cone Beam Computed Tomography for IGRT
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Date
2018
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Ankara Üniversitesi Nükleer Bilimler Enstitüsü
Abstract
In this study, we try to figure out the organ dose of CBCT for head&neck and pelvis’s critical organs with three different CBCT protocols. We also compare the image quality of these protocols and try to find the optimum one for dose and image quality. In this study, organ doses were measured for three different megavoltage CBCT protocols on the Siemens Artiste linear accelerator treatment machine. Organ doses were measured by distributing thermoluminescent dosimeters (TLDs) throughout critical organs of an anthropomorphic (RANDO) phantom. The selected organs include rectum, bladder, femoral heads and small intestine for pelvis imaging and spinal cord, brainstem, thyroid and parotid glands for head and neck imaging. The TLDs placed RANDO phantom was irradiated by using three different imaging protocol and the doses were compared. We have also performed image quality tests for each protocol. We have seen that 15 MU protocol has no difference with 8 MU protocols in the means of image quality and the dose of critical organs is much higher than the others as expected. When we compare 8 MU and 8 MU half ring protocols in the mean values of organ doses, we have seen that the doses of organs changes according to the geometrical placements of organs. Accordingly, while the doses of organs, such as rectum, spinal cord and brainstem, nearby the posterior decreases with the use of 8 MU half protocol, the doses of organs located anterior, such as intestine, thyroid and bladder, increases. It is observed that both the contrast resolution and the spatial resolution of the 8 MU half protocol is better than the 8 MU protocol. After obtaining all this information about MV CBCT protocols, we figure out that the choice of CBCT protocol should be done after treatment planning by considering of the doses and location of the critical organs.
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Keywords
CBCT, IGRT