Impact of number of implanted fiducials on image target localization accuracy / 中华放射肿瘤学杂志

ABSTRACT

Objective To find a proper number of implanted fiducials in order to reconcile both more accurate image tacking and less pain for the patients.Methods The phantom was made of two parts of different materials.The inner part was a ball-cube phantom developed by Accuray Corporation, which could be regarded as a rigid body, with 5 fiducials inside using as the reference to align the whole phantom in the experiment.The outer part was made of additional silicone rubber with two components to simulate soft tissue as a non-rigid body, which was implanted with 8 fiducials inside.All combinations of different number of fiducials were tracked to aquire the target location information, which were then compared with the reference position that was set by the inner 5 fiducials to obtain the deviations of the translation and the rotation parameters.Thus the impact of the number of fiducials on image target localization accuracy could be analyzed easily.Results When 4 fiducials are used for tracking, the decline of translation and rotation errors for every fiducial is largest (0.086 mm and 0.033°).The translation error was decreased by 0.343 mm from 1 to 4 fiducials, while by only 0.077 mm from 4 to 8 fiducials;the same decline was observed for rotation errors (0.131° for 3 to 4 fiducials , and 0.09° for 4 to 8 fiducials , respectively) .Conclusions When 4 fiducials are used for tracking, the decline of errors for every fiducial is maximum.When one more fiducial is adding, the image target localization accuracy can be enhanced obviously from 1 to 4 fiducials, but not as obvious for more than 4 fiducials.