A technique for reducing patient setup uncertainties by aligning and verifying daily positioning of a moving tumor using implanted fiducials

Abstract

This study aimed 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.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 to reduce uncertainties in tumor location in a patient with fiducials implanted in the periphery of a lung tumor.Alignment of fiducial locations in orthogonal projection images with corresponding fiducial locations in 3D data sets can 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.Software that matches fiducial markers on 2D and 3D images is effective for aligning both static and moving fiducials before treatment and can be implemented to reduce patient setup uncertainties.PACS number: 81.40.Wx

Interfractional Reproducibility of Lung Tumor Location Using Various Methods of Respiratory Motion Mitigation

“…Treatment using methods designed to mitigate the effects of respiratory motion (breath hold or gating) with setup based on landmarks other than the actual tumor position requires margins of 0.7 to 0.8 cm. Two possible methods of mitigating systematic uncertainty would be either to set the patient up under image guidance based on cone-beam CT imaging of the tumor or kilovoltage imaging of implanted fiducials (16) or to acquire multiple CT data sets for treatment planning and base the treatment portal on a mean tumor location. The magnitude of setup uncertainty appears to be weakly correlated with the magnitude of GTV excursion, although this correlation may not necessarily be significant, nor does it appear predictive.…”

Locally Advanced Non-Small Cell Lung Cancer and Small Cell Lung Cancer

“…Daily CT scan localization is utilized when more precise localization is necessary (e.g., tumors adjacent to the spinal cord), when the size of the tumor is rapidly changing, or when bony landmarks are not representative of internal anatomy. Prior studies have shown that with daily kV imaging, interfractional variation is approximately 5 mm (Nelson et al 2008 ) and, with CBCT, can be reduced to approximately 3 mm. These are thus the margins that are utilized at our institution (Borst et al 2007 ).…”

Adaptive Radiation for Lung Cancer

“…The authors found that systematic and random uncertainties ranged between 4 and 6 mm in all three directions [ 22 ]. With daily portal imaging, the authors found in a subsequent study that alignment based on implanted fiducials reduced systematic errors in the left-right and superior-inferior direction each by 3 mm [ 23 ]. As a result, daily portal imaging is often utilized to decrease setup error in conventionally fractionated regimens, with a daily setup error of up to 5 mm.…”