Impact Of Changing Gross Tumor Volume Delineation Of Intensity Modulated Radiotherapy On The The Dose Distribution And Clinical Treatment Outcome After Induction Chemotherapy For The Locally Advanced Nasopharyngeal Carcinoma

Background and Objective:The gross tumor volume(GTV) was obviously decreased after neoadjuvant chemotherapy for locally advanced nasopharyngeal carcinoma.This study was to investigate the impact on the target and normal tissue dose distribution and clinical efficacy by changing GTV delineation after neoadjuvant chemotherapy.Methods:Retrospective analysis of 60 primary locoregionally advanced nasopharyngeal carcinoma patient’s clinical data from Jiangxi Provincial Tumor Hospital Department of Radiation Oncology from February 2010 to October 2012.All the patients were treated with two cycles induction chemotherapy(IC) of TP or PF regimen followed by intensity- modulated radiotherapy(IMRT) with conrurrent chemotherapy.The primary GTV was delineated into two parts: the post-IC primary GTV(GTVpost-IC) and the region of pre-IC primary GTV minus GTVpost-IC(GTVpre-post-IC).The tumor target was delineated according to GTVpost-IC,and GTV-pre-IC was overlaid by CTV60. There was Twelve types of TNM pattern according to the 2008 nasopharyngeal carcinoma stage of III ~IVa. To delineate the GTV of twenty-four cases that each type with two cases selected from sixty patients in accordance with above patterns according to GTVpre-IC.Comparing the difference of the dose distribution of two plans based on GTVpost-IC and GTVpre-IC.The clinical treatment outcome and treatment-related toxicity of all patients were observed.Dosimetric analysis was performed on the patients with locoregional relapse.Compareing of the relationship between r GTV and V95 can distinguish which is the type of locoregional recurrence.Results:The post-IC GTV was significantly decreased comparing with the pre-IC GTV(primary GTV 30.42 cc vs. 17.43 cc, P=0.000; lymph nodes GTV 20.14 cc vs.11.51 cc, P=0.04; the GTVnx and GTVnd with an average shrinkage of 32.1%.and 50.21%,respectively. The high dose region was also decreased( Volumes covered by 66 Gy were 435.9 cc vs. 403.3cc, P=0.026; 304.6cc vs. 273.3cc by 70 Gy, P=0.032,)The dose distribution of the PTV before and after neoadjuvant chemotherapy was not significantly different(P>0.05).There were significant differences in the dose of Dmax 、D1cc of spinal cord and the dose of Dmax、D1 of brain stem between pre-IC and post-IC(P<0.05).The compelet response rate was 20% after IC,and 97% three months after radiotherapy. With median follow-up of 36.months, two patients with nasopharyngeal recurrent,one with lymph recurrent.The group of 1、3-year free from locoregional failure survival rate was 98.3%,94.7%separately;1 、 3-year free from progression survival rate was93.2%,70.4% separately. 1、3-year free from distant metastasis survival rate was 93.3,76.3separately. 1,3-year overall survival rate was96.7%, 85.7separately. By analyzing the NPC recurrence model, two patients with nasopharyngeal recurrent and one with lymph recurrent were all of in- fieldfailure.The treatment toxicity of following IC with concurrent chemoradiotherapy was similiar to that of concurrent chemoradiotherapy alone.Conclusions:neoadjuvant chemotherapy could reduced the tumor volume.The following IMRT with post-IC- GTV plan degrade the deglaciation dose to 60 Gy then reduced the high dose region and the dose of spinal cord and brain stem.It is feasible that taking the post-IC- GTV as a tumor target plan does not add treatment toxicity while not reduce the free from rocoregional faliure survival rate and also can obtain good clinical efficacy.