Dosimetric Evaluation of Three Dimensional Conformal and Conventional Treatment Plans of Early Untreated Carcinoma of Nasopharynx

Objective： Conventional external beam irradiation techniques for nasopharyngeal carcinoma have limitations, and improving external beam irradiation techniques is needed to enhance the curative rate. This study was designed to cvaluate the difference in dose distribution of three dimensional conformal radiotherapy （3D CRT） and conventional treatment plan in early untreated nasopharyngeal carcinoma using a three dimensional treatment planning system. Methods： Twenty-two patients with early untreated nasopharyngeal carcinoma were selected. Conventional and 3D CRT plans were made for each of them and compared with respect to target volume coverage （V95）,normal tissue sparing （D50, D33 and D5, etc）, normal tissue complication probability （NTCP）. Results： The average volumetric dose comparison indicated that the V95 of PTVnx70 were 98.22% and 99.99% （P=0.06）, and PTVnd60, 98.41% and 99.63% （P=1.00）, PTV,x60, 98.44% and 99.98% （P=0.03）, PTVnx50, 98.85% and 99.63% （P=0.02） in conventional and 3DCRT treatment plans respectively. With respect to normal tissue sparing, the average D50 of unilateral parotid glands were 51.91 Gy and 64.30 Gy （P=0.00） respectively, and the unilateral temporomandibular joints, 49.98 Gy and 64.47 Gy （P=0.00）, the Dlcc of spinal cords, 44.98 Gy and 48.09 Gy （P=0.00） in 3D CRT and conventional plans. Conclusion： Though only a little bit better dose coverage of target volume in subclinical lesion region was reached in 3D CRT plans, it spared more normal tissues e.g. parotid glands and temporomandibular joints etc and decreased their NTCP while it got the similar dose distribution in target volumes as conventional plans did for these early nasopharyngeal carcinoma cases.

Radiation therapy concurrent with weekly cisplatin therapy for loco-regionally advanced nasopharyngeal carcinoma:outcomes of a clinical trial

Objective:The purpose of this study was to define the maximum tolerated dose(MTD) by describing the doselimiting toxicity(DLT) of weekly cisplatin concurrently with conventional plus 3-dimensional conformal radiotherapy(CT + 3DCRT) in patients with loco-regionally advanced nasopharyngeal carcinoma(NPC).Methods:Patients with loco-regionally advanced NPC(III/IVa stage) were enrolled into a dose-escalating study.Toxicity was graded according to Common Terminology Criteria for Adverse Events version 3.0(CTCAE v3.0).MTD was defined when 2 of 6 patients developed DLT.The starting dose of cisplatin was 15 mg/m2/w,with a subsequent dose escalation of 5 mg/m2/w in cohorts of 3 new patients.CT + 3DCRT was given to the nasopharynx and the upper neck;the lower neck was treated by a single anterior field irradiation.The prescription dose was 70-80 Gy by 35-40 fractions to the nasopharynx gross tumor,and 66-70 Gy by 33-35 fractions to the positive neck lymph nodes.Results:From Jun.2008 to Sep.2009,24 patients received complete chemoradiotherapy,and all of them were eligible for toxicity evaluation.On the first five dose levels of 15 mg/m2/w and 35 mg/m2/w,no patient experienced DLT.On the next dose level of 40 mg/m2/w,1 patient experienced DLT of grade 3 myelosuppression for 1.4 weeks,and among the additional 3 patients,no one developed DLT.On the seventh dose level of 45 mg/m2/w,all the patients developed grade 3 myelosuppression for more than 1 weeks,and the dose-escalating trial stopped.The 23(95.8%) patients achieved clinical complete remission(CR) in the local site;22(91.7%) achieved CR in the regional site,and all patients got CR 3 months later.After a median follow-up of 16.4 months,1 patient developed liver metastases 2 months later,1 patient developed bone metastases 10 months later and 22 kept disease-free survival.Conclusion:The MTD of cisplatin weekly with concurrent CT + 3DCRT for local advanced NPC is 40 mg/m2/w,with myelosuppression as DLT.

基于射束方向优化思想鼻咽癌调强放疗计划正向设计技术

目的探讨使用多叶准直器(MLC)正向设计鼻咽癌调强治疗(IMRT)计划,丰富实现IMRT照射计划设计手段。方法总结分析了自2000年9月—2003年7月间和2005年11月—2006年3月间,在哈尔滨医科大学附属肿瘤医院接受IMRT照射的78例鼻咽癌患者计划,研究鼻咽癌正向IMRT计划设计的技巧。全部病例都采用螺旋CT扫描定位,并在ACQSim工作站上完成勾画PTV、GTV及敏感器官,通过DICOM RT网络将患者定位影像及器官勾画数据资料由ACQsim工作站送入ELEKTA Precise PLAN 3D计划系统。笔者基于射束方向优化思想,根据危险器官和PTV形态预设射束方向,用传统3D计划和正向方式完成主野及补野(或子野)优化设计,获得IMRT计划。结果78个病例计划中,预设鼻咽PTV1的射束方向为六个,颈部PTV2射束方向为前后两个；全部射野数量(含补野、子野,及颈部照射野)为18～27个,平均为24个；以90%相对剂量作为靶剂量,靶区剂量均匀性约在10%左右；适形度以鼻咽部PTV的适形度为评价指标,78例的CI为0．58～0．71,平均为0．65；脑干、脊髓控制剂量均≤55%,平均总机器跳数(MU)为950MU左右；另外,在处理鼻咽部PTV与颈部PTV的射野衔接上,不存在剂量问题。从这78例IMRT计划的剂量分布、DVH数据评估结果、射野总数(含补野、子野)、总MU数等评价结果看,结果很好。结论IMRT是一种目前先进的放疗技术,实现这种照射技术的照射计划从运算方式看分逆向和正向两种,方法技巧运用得当的正向计划可以得到与逆向计划相当的结果,且正向剂量调强计划方式表现出更多的灵活性。