Dosimetric evaluation of IMRT (SS / SW) and VMAT treatment plans for nasopharyngeal cancer

Abstract

Introduction: Radiotherapy of the sphere ORL is still difficult by the presence of complex geometries and very sensitive organs around the target volume.This weapon has benefited from the advances of the VMAT (Volumetric Modulated Arc Therapy) technique, introduced in 2009, it combines the advantages of dynamic arc therapy techniques with the advantages of conformational radiotherapy techniques with intensity modulation (RCMI) by stationary beams.Materials and Methods: The treatment plans of the 4 patients were compared and treated with SS, SW, and VMAT (6MV X-ray beam). The target volumes were three: PTV 70, PTV 63, and PTV56. The organs at risk delineated were the spinal cord, the brainstem, the parotid gland .The dose was delivered once a day, five days a week and in 35 sessions in Integrated Boost (Simultaneaous Integrated Boost (SIB)), aiming to deliver the prescribed dose to the tumor volume while respecting the dose constraints in the organs at risk and minimizing their degree of toxicity.Results: Similar results were found for target volume coverage (Dmax). The SS technique allowed better parotid sparing, which explains its contribution to limiting late complications such as xerostomia. The VMAT technique allows better protection of the brainstem by reducing about 6 Gy, for the spinal cord the doses received were almost equal. Finally, there is no statistically significant difference between the different techniques.Conclusion: All these results conform the conformational capacities of these innovative techniques from a dosimetric and above all clinical point of view. Their ability to cover the target volumes while largely respecting the constraints on organs at risk.