Tumour delineation and cumulative dose computation in radiotherapy based on deformable registration of respiratory correlated CT images of lung cancer patients.

PURPOSE To improve treatment planning in radiotherapy for non-small cell lung cancer by including Respiratory Correlated-Computed Tomography (RC-CT) information in tumour delineation and dose planning. METHODS AND MATERIALS Dense displacement fields were computed using a combination of rigid and non-rigid registrations between RC-CT phases. These registrations have been performed independently between each phase of the respiratory cycle and a reference phase for 13 patients. A manual delineation in the reference frame was propagated to every other phase according to the deformation fields recovered from the inter-phase registrations. Resulting delineations were compared to two manual delineations drawn by two physicians at each phase. On the other hand, dose distributions computed for every phase were deformed towards the reference phase. These distributions were then added on the reference phase to estimate the total dose received by each voxel through the whole respiratory cycle. RESULTS The overlap between the deformed and the manual delineations was not significantly different than the overlap between the delineations made by the two physicians for 11 out of 13 patients thus proving that the method accuracy is comparable to inter-observer variability. Calculation of the effective dose distributions showed that these were conserved after deformation. CONCLUSION We developed a method to use RC-CT information into the radiation treatment planning, including semi-automatic segmentation of lung tumours on each phase of the respiratory cycle and a total received dose per voxel estimation.

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