Evaluation of tumour motion and internal/external correlation in lung SABR

Abstract

Objective: This study aims to analyse lung tumour motion and to investigate the correlation between the internal tumour motion acquired from four-dimensional computed tomography (4DCT) and the motion of an external surrogate. Methods: A data set of 363 4DCT images was analysed. Tumours were classified based on their anatomical lobes. The recorded gross tumour volume (GTV) infor-mation included the centroid GTV motion in the supe-rior–inferior, anteroposterior and left-right directions, and in three-dimensions (3D). For the internal/external correlation, the RPM surrogate breathing signals of 260 patients were analysed via an in-house script. The external motion was correlated with the 3D centroid motion, and the maximum tumour motion via Spear-man’s correlation. The effect of tumour volume on the amount of motion was evaluated. Results: The greatest 3D tumour amplitude was found for tumours located in the lower part of the lung, with a maximum of 26.7 mm. The Spearman’s correlation of the internal 3D motion was weak in the upper (r = 0.21) and moderate in the middle (r = 0.51) and the lower (r = 0.52) lobes. There was no obvious difference in the correlation coefficients between the maximum tumour displacement and the centroid motion. No correlation was found between the tumour volume and the magni-tude of motion. Conclusion: Our results suggest that tumour location can be a good predictor of its motion. However, tumour size is a poor predictor of the motion. Advances in knowledge: This knowledge of the distribu-tion of tumour motion throughout the thoracic regions will be valuable to research groups investigating the refinement of motion management strategies.