鼻咽癌螺旋断层放射治疗在不同射野宽度下的剂量学研究

Dosimetric study of HT under different field widths for NPC

目的:探讨鼻咽癌(NPC)螺旋断层放射治疗(HT)在不同射野宽度(FW)下的剂量学特性。方法:选取在医院就诊的20例NPC患者,将其病例资料数据传至治疗计划系统,固定螺距为0.287、调制因子(MF)为2.5两个参数,仅改变FW,对每例患者分别设计3个放射治疗计划。评价靶区95%的靶体积所接受的剂量(D95%)、100%处方剂量的靶体积(V_(10)0)、适形度指数(CI)、均匀性指数(HI)和危及器官(OAR)受照最大剂量(D_(max))和平均剂量(D_(mean))、计划设计时间和计划出束时间。结果:鼻咽计划肿瘤体积(PGTVnx)、转移性淋巴结计划肿瘤体积(PGTVnd)和临床计划靶区(PCTV2)的靶区覆盖度D95%射野宽度1.048 cm优于2.512 cm和5.048cm,差异有统计学意义(F=7.758,F=6.542,F=8.058;P<0.05);CI和HI均表现为FW越小越好。3组计划的OAR参数均满足临床要求,OAR 1.048 cm计划参数优于2.512 cm,OAR 2.512 cm计划参数优于5.048 cm,右侧眼晶状体D_(max)、左侧眼晶状体D_(max)、右侧眼球D_(max)、左侧眼球D_(max)、右侧视神经D_(max)、视交叉D_(max)、右侧颞下颌关节D_(max)、左侧颞下颌关节D_(max)、右侧内耳D_(max)、左侧内耳D_(max)、脊髓D_(max)、脑干D_(max)、下颌骨D_(max)、右侧腮腺V_(10)、右侧腮腺V_(30)、左侧腮腺V_(20)、左侧腮腺V_(30)和口腔V_(40)各组之间的差异有统计学意义(F=170.127,F=156.034,F=107.102,F=86.095,F=5.091,F=7.616,F=79.973,F=79.488,F=49.041,F=43.400,F=7.713,F=5.070,F=7.588,F=8.179,F=5.756,F=6.287,F=6.020,F=12.604;P<0.05)。计划设计时间随FW减小而显著缩短,机器出束时间和机架旋转圈数随FW减小显著增加。结论:在选择HT参数时需综合考虑,根据NPC的不同分期以实事求是为原则做出最佳选择。综合以往研究与本研究,建议在治疗患者较多的情况下NPC HT计划射野宽度选用2.512cm。

Objective:To investigate the dosimetric characteristics of helical tomotherapy(HT)under different field width(FW)for nasopharyngeal carcinoma(NPC).Methods:Twenty patients with NPC who admitted to hospital were randomly selected,and the data of them were transferred to the treatment plan system.The two parameters included screw pitch(pitch=0.287)and modulation factor(MF=2.5)were fixed,and only the FW was changed.Three radiotherapy plans were designed for each patient.And then,the exposure dose of 95%target volume of target region(D95%),the target volume of 100%prescription dose(V_(10)0),conformity index(CI),homogeneity index(HI),the maximum dose and average dose of the exposure of organ at risk(OAR),plan design time and the time of beaming in plan were further evaluated.Results:The FW of D95%target coverage of nasopharynx planning gross tumor volume(PGTVnx),metastatic lymph nodes planning gross tumor volume(PGTVnd)and planning clinical target volume-2(PCTV2)was1.048 cm that was better than those of 2.512 cm and 5.048 cm,and the differences were statistically significant(F=7.758,F=6.542,F=8.058,P<0.05).Both CI and HI showed that smaller FW was better.All of OAR parameters of the 3 groups of plans met the clinical requirements.OAR 1.048 cm plan parameters were better than that of 2.512 cm,and OAR2.512 cm plan parameters were better than that of 5.048 cm.The differences of R eye lens D_(max),L eye lens D_(max),R eyeball D_(max),L eyeball D_(max),R optic nerve D_(max),optic chiasm D_(max),R temporal-mandibular joint D_(max),L temporal-mandibular joint D_(max),R inner ear D_(max),L inner ear D_(max),spinal cord D_(max),brain stem D_(max),mandible D_(max),R parotid grand V_(10) and V_(30),L parotid grand V_(20) and V_(30),and oral cavity V_(40) among three kinds of FWs were significant(F=170.127,F=156.034,F=107.102,F=86.095,F=5.091,F=7.616,F=79.973,F=79.488,F=49.041,F=43.400,F=7.713,F=5.010,F=7.588,F=8.179,F=5.756,F=6.287,F=6.020,F=12.604,P<0.05).The planned design time significantly was shortened with the decreasing of FW.And the beaming time of machine and the rotation number of rack significant increased with the decreasing of FW.Conclusion:The determination should be comprehensively considered when chooses the HT parameters.And the best choice should be determined according to the practical and realistic principle of the NPC different stages.On the basis of comprehensive results of primarily research and the exploration of this project,this paper suggests that the FW of NPC HT plan should choose 2.512 cm under the condition with more patients.