Motion-compensated Cone-beam CT For Accurate Online Assessment Of The Position Of Lung Tumours

Main Category: Radiology / Nuclear Medicine
Also Included In: Lung Cancer;  Cancer / Oncology;  Respiratory / Asthma
Article Date: 22 Sep 2008 - 4:00 PDT

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High precision radiotherapy requires accurate tumour localisation for patient positioning just prior to treatment. Respiratory motion induces artifacts in cone-beam (CB) CT images of the thorax and upper abdomen which can prevent an accurate localisation of tumours. Respiration-correlated reconstruction has been used to correct for this motion. Because only a subset of the CB projections is used to reconstruct each frame of the 4D CBCT image, long acquisition times are required to obtain adequate image quality. We propose instead online motion-compensated (MC) CBCT, i.e. the compensation of the respiratory motion during the reconstruction from all the CB projections using a prior estimation of a model of the respiratory motion. A model of the patient respiratory motion, represented by a 4D deformation vector field (DVF), was constructed from the 4D planning CT with deformable re¬gistration. The respiratory motion during the CB acquisition was derived from this model depending on the phase of a respiratory signal extracted from the X-ray images. The motion was compensated in the filtered-backprojection reconstruction by warping each backprojection according to the 4D DVF.

The method was evaluated on 26 CBCT scans of 3 lung cancer patients acquired on an Elekta Synergy with the two protocols used for static CBCT (1 min scan time) and 4D CBCT (4 min scan time).

MC-CBCT corrected most of the respiratory motion artifacts as in 4D CBCT thus validating the use of a prior model. The proposed method is therefore an alternative solution to assess the position of lung tumors. Contrary to 4D CBCT, MC-CBCT uses all the CB projections to reconstruct a 3D CBCT which allows the reduction of the acquisition time (from 4 min to 1 min in our institution) while obtaining a higher image quality.

Rit Simon et al. The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital (Radiotherapy), Amsterdam , Netherlands

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