Volume variation of the parotid gland during adaptive radiotherapy

Radiation therapy is defined as a type of cancer treatment process using radiation principle at different times for the case of external radiation 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 adaptively for the purpose of maintaining optimal treatment objectives. In order to track the deformable image of biological target (ie. tumor, organ,...) such as the parotid gland, a 3D reconstruction is needed. 5 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. The difficulty is that this manual countour is generally different from one expert to another due to several uncertainties. Thus, 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 is calculated for each patient. The obtained results show a decreasing of the volume of the parotid from one week to other one, which causes the shifting of the identified center of gravity of the reconstructed volume. According to the obtained results, a classification of the patient per volume changes can be made, allowing in the future to adapt the radiation plan with the gland volume time-evolution.