Deformable image tracking of the parotid gland for adaptive radiotherapy application.

Radiation therapy is a type of cancer treatment using radiation at different times defined as treatment sessions, distributed over different weeks. In each session, we have to determine and define the optimal treatment parameters for the patient. The aim of Adaptive Radiotherapy Treatment (ART) is to identify any change of initial parameters during the treatment course and modify the treatment plan for the purpose of maintaining optimal treatment objectives. In order to track the deformable image of biological organ such as the parotid gland, a 3D reconstruction is needed. 10 patients were scanned at the medical center of Oscar Lambret (Lille, France) using CT scan as imaging modality. The contours of the acquired images were extracted manually by the expert. Relaxed bi-cubic Bézier spline surface has been used in our study for the purpose of automatically reconstruction of the biological organ. Once the reconstruction is accomplished, the volume of the parotid gland at each session of treatment has been calculated for each patient. The obtained results show a decreasing of the volume of the parotid from one week to other one and a shifting of the detected center of gravity. These variations should be used to build a predictive model for adaptive robotized radiotherapy.