Adaptive approach for nasopharyngeal carcinomapatients during Volumetric Modulated Arc Therapytreatment (VMAT)

Patients with head-and-neck cancers receiving radiotherapyshow significant anatomical and dosimetric changes, especially during thelatter part of treatment. the aim of this study is to evaluate the dosimetriceffects of an adaptive volumetric modulated arc therapy (vmat) treatmentprotocol for patients with locally advanced nasopharyngeal cancer (npc).material and methods: ten patients treated with vmat have benefited froma second computed tomography scan (ct2) after 15 fractions in order toapply a new adapted plan. a hybrid plan has been generated applying theoriginal treatment plan configuration beam to the second ct scan. the dose–volume histograms (dvhs) of hybrid and adapted plans have been compared.results: at the end of the 3rd week of treatment, ct2 shows a considerableshrinkage of gtv n70 volume (45.2%) and a diminution of the left and rightparotid glands volume (21.1%, 20.6% respectively). compared to the initialplans, hybrid plans reveal that the dose delivered to target volume gtv n70decreased by 15.2%, and the v30 of the left and right parotid glands increasedby 47.3% and 25.6% respectively. however, there is no significant differencefor the d2 of the brainstem and spinal cord. conclusion: our adaptive vmatprotocol improves dosimetric results in terms of gtv n70 coverage andnontoxic doses to parotid glands