Clinical Study Of Nasopharyngeal Carcinoma Treated By Tomotherapy

Objective:To evaluate the preliminary clinical outcome of 57 nasopharyngeal carcinoma(NPC) patients treated with TomoTherapy.Methods:Between September 2007 and February 2009,57 continuous newly diagnosed NPC patients were treated with TomoTherapy system.The distributions of clinical stages according to the FUZHOU 92's staging system were 5,15,31 and 6 for stageⅠ,Ⅱ,ⅢandⅣ,respectively.The prescription dose was 64～76Gy/32～33F to gross tumor volume(pGTVnx) and positive lymph nodes(GTVnd),with 58～66Gy/32～33F to high risk clinical target volume (CTV1),while delivering 49.5～60Gy/32～33F to low risk clinical target volume (CTV2).Pre-treatment megavoltage CT scans were registered with the planning CT images to correct setup errors and calculate M_PTV.Acute toxicities were evaluated with the established RTOG/EORTC criteria,and preliminary tumor response was evaluated at the same time.Results:The median follow-up was 9 months(2～18 months).The dose-volumn histograms showed that the average dose delivered to pGTVnx, GTVnd,CTV1 and CTV2 was 70.3Gy,69.7 Gy,60.5Gy and 54.1Gy,respectively. The average therapeutic time was 476.1±65.9 seconds.Setup errors were 1.381mm,1.589mm and 0.895mm in X,Y,Z axes.M_PTV were 3.92 mm,4.22 mm, and 2.77mm in 3 directions.Acute skin toxicities of grade 1,2 and 3 were 77.2%, 14.0%and 5.3%;acute mucositis of grade 1～2 and 3 were 96.5%and 3.5%;acute xerostomia of grade 1,2,and 3 were 49.1%,45.6%,and 0%,respectively. Average weight loss was 11.0%(0%～22.2%).Eleven patients achieved complete remission(CR),38 achieved partial remission(PR) and 8 had stable disease(SD) for the primary nasopharyngeal tumor.Fourteen patients achieved CR,25 achieved PR and 4 had SD for regional lymph nodes.The remission rate of primary lesion and positive nodes were 86.0%and 90.7%,respectively.No local recurrence was detected.Three patients developed distant metastasis.Conclusions:Helical TomoTherapy has a better homogeneity,steeper dose gradient and better protection for organs at risk in NPC radiotherapy with a short therapeutic time.IGRT technique can correct setup errors and provides the evidence for CTV expanding.The incidence of severe acute toxicities is low. Objective:To quantify parotid gland and spinal cord dose variations for nasopharyngeal carcinoma patients using helical tomotherapy megavoltage computed tomography(MVCT) and Planned Adaptive application.Methods:Five local advanced nasopharyngeal carcinoma patients treated by TomoTherapy were selected,each patient received 70Gy/35F.Daily MVCT scans were registered with the planning CT images to correct the patient setup errors. Contours of parotid glands were drawn every four fractions and locations of spinal cord were corrected by MVCT IGRT system every two fractions to a total number of 135 times.The actual doses delivered in these organs were calculated using the Planned Adaptive application of TomoTherapy system.Result:Average volume of parotid gland decreased by 42%(left) and 33% (right) at the end of treatment,respectively.En average,parotid V1 increased by 26.0%(left) and 31.4%(right),and the D50 increased by 15.8%(left) and 17.3% (right),respectively.The average maximal dose of the spinal cord increased by 1.23%.Conclusions:During radiation therapy course,the volumn parotid glands decrease leading a higher actual dose,while the maximal dose of spinal cord chages little.Constant monitoring anatomic changes of organs at risk and selective replanning,by using adaptive radiation therapy technique,is necessary for protecting these organs.