Dosimetric evaluation of IMRT Step and Shoot/ Sliding and Window (SS / SW) and VMAT Treatment Plans for Nasopharyngeal Cancer

Introduction: Radiotherapy of Oto-Rhino-Laryngology (ORL) sphere is difficult due to complex geometries and very sensitive organs around the target volume. This weapon has benefited from the advances of the Volumetric Modulated Arc Therapy (VMAT) technique that combines the advantages of dynamic arc therapy techniques with those of Conformal Radiotherapy with Intensity Modulated (CRIM) by stationary beams. Material and Methods: The treatment plans of 10 patients were compared and treated with Intensity Modulated Radiation Therapy (IMRT) Step and Shoot (SS), Sliding window (SW), and VMAT (6MV X-ray beam). Three target volumes were used: PTV ث Gy, PTV 63 Gy, and PTV 56 Gy. The organs at risk 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 Simultaneous Integrated Boost (SIB). Results: The SS technique permitted better parotid sparing, inducting thus to limiting late complications such as xerostomia. The VMAT technique led to better protection of the brainstem by reducing about 6 Gy while for the spinal cord the doses received were almost equal. There was no statistically significant difference between the different techniques. Conclusion: The results confirm the conformational capacities of these innovative techniques, from a dosimetric and above all clinical point of view as well as their ability to cover the target volumes while largely respecting the constraints on organs at risk.