Effects of image distortion and Hounsfield unit variations on radiation treatment plans: An extended field-of-view reconstruction in a large bore CT scanner

This study aimed to evaluate the effect of image distortion and Hounsfield unit (HU) variation due to the extended field-of-view (eFOV) of the large-bore (LB) computed tomography (CT) on dose distribution. Both home-made inhomogeneity and breast phantoms were scanned at the geometric center position and four different offset positions. We also performed dose optimizations based on different breast phantom CT sets for evaluating the effects of image artifacts on the intensity-modulated radiation techniques. The volume changes were 0.0% to 0.5% in the air, −0.5% to 3.0% in the water, and 4.0% to 5.0% in the high-density material of the inhomogeneity phantom. Both phantoms scanning results indicate that more distortions occurred in the eFOV area due to the biased scanning center. The gamma index differences ranged from 0.87% to 4.87% for the FIF plan and from 0.52% to 6.26% for the VMAT plan. This resulted in decrease of the minimum (7.3–13.1%), maximum (−0.8–2.2%), and mean doses (−0.2–4.4%). We recommend that it should be evaluated whether the applied CT would have an appropriate eFOV range for clinical radiation treatment planning for patients.