The Study Of Target Dose Distribution Changes And Efficacy Of Image-guided Intensity Modulated Radiation Therapy With Concurrent Chemotherapy In The Treatment Of Nasopharyngeal Carcinoma

Objective：To analyze the target dose distribution changes and evaluate the short-termefficacy in the treatment of nasopharyngeal cancer by image-guided intensity modulatedradiation therapy (IGRT) technology with concurrent chemotherapy.Methods: From January2009to June2010,42patients who were pathologicallydiagnosed as nasopharyngeal carcinoma were admitted. including28males and14females, aged32-72years, mean age was48years. According to the AJCC2008staging system, in which8cases were stage II,24cases were stage III and10caseswere stage IVA. All patients underwent a simulation CT, and the images were uploaded tothe Xio treatment therapy system(TPS). The target volume and normal tissues werecontoured on the CT image and then the treatment IMRT plan was developed using6MVX,9coplanar fields. The dose to the Nasopharyngeal tumor and lymph node was66Gy/30F/6W, dose to the nasopharynx subclinical lesions and neck lymphatic drainagearea was60Gy/30F/6W. Daily orthogonal images were acquired in the patient treatmentposition to compare with the original treatment planning image, and the patientpositionning error was corrected in three dimensions, then the radiation therapy wasimplemented. Each patient underwent a simulation CT scan weekly to analyz the dosedistribution changes of the target and the normal tissues. Concurrent chemotherapyregimen was cisplatin plus docetaxel every3weeks, during radiotherapy the regimen ofdocetaxel40mg/m2weekly was used. The chemotherapy was started within the beginningof the radiaotherapy. acute toxicity was evaluated after the end of chemoradiotherapy.Lesions were evaluated tow months after the radiotherapy. All patients were followed upuntil June2013, to evaluate the three-year disease free survival and overall survival. Results: The average volume of GTV1was39.19cc before radiotherapy, GTV2was16.59cc, at4th and6th week of the radiotherapy course the average reduction of GTV1were26.41%,62.68%, for GTV2were28.43%and53.93%respectively. Before treatment,the average volume of bilateral parotid was24.16cc, after4weeks of radiation therapy,the average volume of parotid was19.04cc, after6weeks the average volume of theparotid gland was17.54cc. For normal tissues, spinal cord, brainstem, temporal lobe, theinner ear, parotid gland, the dose was increased after3and5weeks radiation comparewith the original plan.3-year follow-up, disease-free survival and overall survival rateswere76.19%and85.71%. Most patients got acute toxicity of degree II. Severe acutereaction of degree IV was not observed.Conclusion:1. In the nasopharyngeal IMRT process, the actual dose distribution ofthe tumor will be some difference to the original plan, but the CTV actual dose is above95%of the prescribed dose, although after a few weeks of treatment the tumor targetvolume and shape changes, the difference was not significant. The dose to the Normaltissues in the whole course of treatment will be increased compared with the original plan,but the increase is within the dose tolerance. To adjust the IMRT plan according to the sizeand morphological changes in tumor and normal tissue of patients during the treatmentcourse is a good strategy to increase tumor dose and to protect the normal tissues moreefficiently.2. The treatment toxicty of degree IV did not occur in skin and mucosal, exceptmyelosuppression of degree IV occurred in one case. patient tolerance is acceptable,image-guided intensity-modulated radiotherapy with concurrent chemotherapy in thetreatment of nasopharyngeal carcinoma can achieve good short-term effect.