The Applied Research Of Phased Intensity-modulated Radiotherapy In The Treatment Of Local-advanced Nasopharyngeal Carcinoma

Objective： The aim of this study was to evaluate prospectively thevolumetric and dosimetric changes of target volumes and organs at risk(OARs) during the course of intensity-modulated radiation therapy (IMRT)for local-advanced nasopharyngeal carcinoma (NPC) and the necessity andthe best timing of phased intensity-modulated radiotherapy.Methods：20local-advanced nasopharyngeal carcinoma patients treated byconcurrent chemotherapy and IMRT were included. CT and MR images wereacquired for each patient before treatment and at weeks2,3,4,5and6during treatment. The target volumes and OARs were contoured based onthe fused CT-MRI images and hybrid plans were generated. The volumetricchanges and the dosimetric changes were measured by comparing the originalplan and hybrid plans.Results：Significant volumetric changes of target volumes and parotidgland were observed during the treatment course. The primarynasopharyngeal tumor (GTVnx), CTV1, involved lymph nodes (GTVnd) and leftand right parotid glands, shrank at a mean rate of14.7%,11.56%,11.40%,6.54%,6.78%per treatment week, respectively. There were no significantdosimetric differences in GTVnx, GTVnd, CTV1, the spinal cord and brainstem when comparing the initial CT imaging before treatment with thesubsequent weekly CT imaging. On the contrary, the differences in thedosimitric parameters to the bilateral parotid glands were significant (F=6.73, P=0.007; F=7.43, P=0.007).Conclusion：Remarkably volumetric changes were observed, however thedosimetric changes were inconspicuous except parotid. Phasedintensity-modulated radiotherapy might bring benefits for protecting theparotid gland.