Adaptive approach for nasopharyngeal carcinoma patients during Volumetric Modulated Arc Therapy treatment (VMAT)

Background: Patients with head-and-neck cancers receiving radiotherapy show significant anatomical and dosimetric changes, especially during the latter part of treatment. The aim of this study is to evaluate the dosimetric effects of an adaptive Volumetric Modulated Arc Therapy (VMAT) treatment protocol for patients with locally advanced nasopharyngeal cancer (NPC). Material and methods: Ten patients treated with VMAT have benefited from a second computed tomography scan (CT2) after 15 fractions in order to apply a new adapted plan. A hybrid plan has been generated applying the original 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 3 week of treatment, CT2 shows a considerable shrinkage of GTV N70 volume (45.2%) and a diminution of the left and right parotid glands volume (21.1%, 20.6% respectively). Compared to the initial plans, hybrid plans reveal that the dose delivered to target volume GTV N70 decreased by 15.2%, and the V30 of the left and right parotid glands increased by 47.3% and 25.6% respectively. However, there is no significant difference for the D2 of the brainstem and spinal cord. Conclusion: Our adaptive VMAT protocol improves dosimetric results in terms of GTV N70 coverage and nontoxic doses to parotid glands.