A Technique for Reducing Patient Setup Uncertainties by Aligning and Verifying Daily Positioning of a Moving Tumor using Implanted Fiducials

Abstract

Purpose: The purpose of this study is to validate and implement a methodology in which fiducials implanted in the periphery of lung tumors can be used to reduce uncertainties in tumor location.

Methods and Materials: Alignment software that matches marker positions on two-dimensional (2D) kilovoltage portal images to positions on three-dimensional (3D) computed tomography data sets was validated using static and moving phantoms. This software also was used on a patient with fiducials implanted in the periphery of a lung tumor to reduce uncertainties in tumor location.

Results: Aligning fiducial locations in orthogonal projection images with corresponding fiducial locations in 3D data sets can be used to position both static and moving phantoms with an accuracy of 1 mm. In a patient, alignment based on fiducial locations reduced systematic errors in the left-right direction by 3 mm and random errors by 2 mm, and random errors in the superior-inferior direction by 3 mm as measured by anterior-posterior cine images.

Conclusions: Software that matches fiducial markers on 2D and 3D images is effective for aligning both static and moving fiducials prior to treatment and can be implemented to reduce patient setup uncertainties.