Abstract
Respiration and anatomical variation during radiotherapy (RT) of lung cancer yield dosimetric uncertainties of the delivered dose, possibly affecting the clinical outcome if not corrected for. Adaptive radiotherapy (ART), based on deformable image registration (DIR) and Deep-Inspiration-Breath-Hold (DIBH) gating can potentially improve the accuracy of RT. Purpose: The objective was to investigate the performance of contour propagation on repeated CT and Cone Beam CT (CBCT) images in DIBH compared to images acquired in free breathing (FB), using a recently released DIR software. Method: Three locally advanced non-small cell lung cancer patients were included, each with a planning-, midterm- and final CT (pCT, mCT, fCT) and 7 CBCTs acquired weekly and on the same day as the mCT and fCT. All imaging were performed in both FB and DIBH, using Varian RPM system for respiratory tracking. Delineations of anatomical structures were performed on each image set. The CT images were retrospective rigidly and deformable registered to all obtained images using the Varian Smart Adapt v. 11.0. The registered images were analysed for volume change and Dice Similarity Coefficient (DSC). Result: Geometrical similarities were found between propagated and manually delineated structures, with a slightly favour of FB imaging. Special notice should be taken to registrations where image artefacts or low tissue contrast are present. Conclusion: This study does not support the hypothesis that DIBH images perform better image registration than FB images. However DIR is a feasible tool for ART of lung cancer.
Highlights
Anatomical changes and variations due to respiration influence the accuracy of imaging, treatment planning and treatment delivery, and may affect the outcome of the planned treatment if not corrected for [1]
This study does not support the hypothesis that DIBH images result in better image registrations when using a modified demons type algorithm for deformable image registration
Notice should be taken to image artefacts and bad image quality that can affect the outcome of deformable image registration (DIR)
Summary
Anatomical changes and variations due to respiration influence the accuracy of imaging, treatment planning and treatment delivery, and may affect the outcome of the planned treatment if not corrected for [1]. In ART, the treatment plan is adjusted during the course of treatment to minimize the divergence from the planned treatment, in terms of target dose coverage and spearing of dose to adjacent healthy organs at risk. ART has the potential to account for major anatomical changes not accounted for by applied margins [1].
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