Résumé:
The principle of external radiotherapy in the treatment of nasopharyngeal cancer is to deliver a total dose of 70Gy over 6.5 to 7 weeks of treatment. This dose is calculated from anatomical data from an initial CT (Computed Tomography) imaging acquired before the start of treatment. However, it is suggested that the acquisition of a single CT imaging is not sufficient to follow the anatomical changes and their dosimetric consequences occurring during treatment by external radiotherapy. The multiple and regular acquisition of CT imaging and replanning during treatment seems to be able to monitor anatomical changes and their dosimetric impacts. Our work focuses on the adaptation of VMAT radiotherapy treatments by exploring the anatomical and dosimetric indicators that can help make a decision on the need of a replanification and the appropriate time for, and to highlight the contribution of adaptive radiotherapy in the treatment of patients with nasopharyngeal cancer. To do this, the volumetric changes of the parotid glands, the target volume GTV N70, and the external contour of these patients were evaluated and compared based on 3D imaging acquired throughout the treatment. In addition, the dosimetric variations of the V30 of the two parotid glands, the D95 of the GTV N70, the D2 of the brain stem and the spinal cord were quantified from the plans calculated for each acquired CT imaging. The results of our work show that a second CT imaging performed after the third week of treatment is necessary and sufficient for the identification of anatomical changes and the monitoring of dosimetric consequences, in order to improve tumor control of the disease and the quality of life of patients.
