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

Christopher Nelson,Bum Choi,Susan Tucker,Tina Briere,Sastry Vedam,George Starkschall,Joe Y Chang,Kara Bucci,Rodolfo C Morice,Rajat J Kudchadker,Lei Dong,Peter Balter

doi:10.1120/jacmp.v9i4.2766

Christopher Nelson, Bum Choi + Show 10 more

Open Access

https://doi.org/10.1120/jacmp.v9i4.2766

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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

Highlights

Provided that the spatial relationship between the lasers in the treatment room and the radiation isocenter of the treatment machine is accurately maintained, alignment of patient surface marks with the lasers should accurately align the patient treatment isocenter with the radiation isocenter of the treatment machine
When setting up the patient using external markers, sufficient margins are added to the clinical target volume (CTV) to account for daily variations in the relative position of the tumor with respect to the surface marks.[4]. Ideally, the margin that accounts for these variations in tumor location is minimized to reduce excess toxic effects to normal tissue
Fiducials implanted in the prostate have been used extensively for patient alignment before treatment.[21,22] For lung tumors, Shirato et al[7,8] have extensively used fiducials implanted near the tumor for both patient alignment and gated delivery of the treatment beam

Summary

Introduction

Provided that the spatial relationship between the lasers in the treatment room and the radiation isocenter of the treatment machine is accurately maintained, alignment of patient surface marks with the lasers should accurately align the patient treatment isocenter with the radiation isocenter of the treatment machine. The patient is not a uniform rigid body and respiratory motion, cardiac motion, and movement of the skin marks introduce uncertainties into the position of the patient’s isocenter. To verify the accuracy of the isocenter position, the patient undergoes procedures such as kilovoltage (kV) or megavoltage (MV) imaging.[1,2,3]. 111 Nelson et al.: A technique for reducing patient setup uncertainties. Surface marks are used for patient setup, the anatomy being treated is typically located deep within the patient. When setting up the patient using external markers, sufficient margins are added to the clinical target volume (CTV) to account for daily variations in the relative position of the tumor with respect to the surface marks.[4] Ideally, the margin that accounts for these variations in tumor location is minimized to reduce excess toxic effects to normal tissue. Small margins increase the possibility of a geometric miss of the CTV

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