Abstract
The purpose of this study was to evaluate the geometric accuracy of thoracic anatomic landmarks as target surrogates of intrapulmonary tumors for manual rigid registration during image-guided radiotherapy (IGRT). Kilovolt cone-beam computed tomography (CBCT) images acquired during IGRT for 29 lung cancer patients with 33 tumors, including 16 central and 17 peripheral lesions, were analyzed. We selected the "vertebrae", "carina", and "large bronchi" as the candidate surrogates for central targets, and the "vertebrae", "carina", and "ribs" as the candidate surrogates for peripheral lesions. Three to six pairs of small identifiable markers were noted in the tumors for the planning CT and Day 1 CBCT. The accuracy of the candidate surrogates was evaluated by comparing the distances of the corresponding markers after manual rigid matching based on the "tumor" and a particular surrogate. Differences between the surrogates were assessed using 1-way analysis of variance and post hoc least-significant-difference tests. For central targets, the residual errors increased in the following ascending order: "tumor", "bronchi", "carina", and "vertebrae"; there was a significant difference between "tumor" and "vertebrae" (p=0.010). For peripheral diseases, the residual errors increased in the following ascending order: "tumor", "ribs", "vertebrae", and "carina". There was a significant difference between "tumor" and "carina" (p=0.005). The "bronchi" and "carina" are the optimal surrogates for central lung targets, while "ribs" and "vertebrae" are the optimal surrogates for peripheral lung targets for manual matching of online and planned tumors.
Highlights
A major advancement in radiotherapy in recent years is the advent of image-guided radiation therapy (IGRT)
It is necessary to screen the surrogate of lung tumors for online image guidance
We reported the initial results of the anatomic accuracy of several candidate surrogates for image-guided lung radiotherapy according to the residual errors (REs) after manual matching
Summary
A major advancement in radiotherapy in recent years is the advent of image-guided radiation therapy (IGRT). An EPID with a well-thought-out correction protocol may be sufficient for some disease sites (e.g., the brain, head, and neck) where bony landmarks can be reliably used to determine the target and critical organ locations (Bel et al, 1995; de Boer et al, 2001). Threedimensional (3D) imaging devices, such as kV CBCT, can generate images with improved soft-tissue contrast by using acceptably low imaging doses. In comparison to EPIDs, IGRT by using 3D imaging may improve tumor targeting during the delivery of radiotherapy
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