European Journal of Molecular & Clinical Medicine ISSN 2515-8260 Volume 08, Issue 03, 2021 979 Dosimetric analysis of VMAT Irradiation in Nasopharyngeal Carcinoma: A Moroccan Radio Oncology Center's experience Bouchra Amaoui 1* , Slimane Semghouli 2 , Dounia Mouhssine 3 , Abdelaziz Bayla 3 , abdellatif Bouih 3 , Nawal Bouih 3 , Hicham Tamri 3 , Mohamed El Mourchid 3 , and Noureddine Benjaafar 4 1 Faculty of Medicine and Pharmacy, Ibn Zohr University, Agadir Morocco 2 Higher Institute of Nursing Professions and Health Techniques Agadir, Morocco 3 Al Kindy Treatment Center of Oncology and Diagnosis Casablanca, Morocco 4 Radiotherapy Department, National Institute of Oncology Rabat, Morocco * Corresponding author: Email: b.amaoui@uiz.ac.ma Abstract Introduction: Volumetric Modulated Arc Therapy (VMAT) is a technique increasingly used in radiotherapy. It was recently introduced in Morocco. Furthermore, technological advances allow the use of conformal radiotherapy to be phased out and replaced by VMAT technique for some locations. This study aims to evaluate the efficacy and quality of treatment with VMAT of nasopharyngeal cancer. Methods: Twenty patients with non-metastatic nasopharyngeal cancer treated curatively by VMAT were studied at the Al Kindy Oncology Center in Casablanca. The dose was delivered using two arcs at a dose of 70 Gy in 35 fractions. The optimization process was performed using the photon optimizer (PO) algorithm, which is available from versions 13.5.35 and beyond of the Varian Eclipse radiotherapy treatment planning system (Varian Medical Systems, Palo Alto, CA). Dosimetric data were collected from dose-volume histograms for target volumes (PTV) and organs at risk (OARs). The homogeneity index (HI) and the conformity index (CI) were calculated. The acute and late toxicities associated with radiotherapy were observed, and the evolution and follow-up of patients were carried out. Results: For high risk (HR), intermediate risk (IR), and low risk (LR) PTVs, the D 95% was (95.54±1.61), (103.00±1.66) and (100.00±1.90)%, respectively, while the D 2% was (105.15±1.11), (105.20±1.42) and (104.56 ±1.25)%, respectively. For HR PTV, CI and HI were (0.98 ± 0.02) and (0.12 ± 0.03), respectively. For late toxicity, there were no reports of grade IV toxicity or grade III xerostomia. In contrast, a drop in the hearing of grade III was reported in 10% of patients. Patients' evolution was marked by a locoregional recurrence rate of 15% and a specific death rate of 20%. Conclusion: The VMAT technique allows an excellent coverage of the target volumes while sparing the OARs particularly the nerve structures and the salivary glands. Keywords: Rhino-pharyngeal cancer, VMAT, Dosimetry, Toxocity