早期鼻咽癌常规放疗相邻野衔接设计的剂量学研究

目的　应用三维治疗计划系统对早期鼻咽癌常规放疗相邻野衔接设计方案进行剂量学研究，探讨其在临床放疗中的价值。方法　对５例早期初治鼻咽癌患者，设计面颈联合野与下颈锁骨上单前野衔接移位方案，即先给予面颈联合野ＤＴ１９Ｇｙ／１０ｆ，下颈锁骨上单前野Ｄｍ２５Ｇｙ／１０ｆ，后将两野衔接上移１５ｃｍ，继续予两野至ＤＴ３８Ｇｙ／２０ｆ和Ｄｍ５０Ｇｙ／２０ｆ；面颈缩野与上后颈电子线照射野衔接时设计５°水平（９５°和２６５°）共线成角及０°水平重叠０５ｃｍ两种方案，两野ＤＴ２０Ｇｙ／１０ｆ。应用三维治疗计划系统比较其与常规衔接方案剂量分布。结果　（１）面颈联合野与下颈锁骨上单前野常规衔接方案衔接处组织受照最高剂量以及ＤＴ５２Ｇｙ以上受照体积分别为ＤＴ（５６.２７±１.８１）Ｇｙ和（１２.４９±８.２９）ｃｍ³，衔接移位方案分别为ＤＴ（５２.８２±１.３）Ｇｙ和（２.１３±４.１６）ｃｍ３，差异均有统计学意义（Ｐ＜０.０５）。（２）面颈缩野与上后颈电子线照射野衔接时，常规０°水平共线衔接两野相邻处存在低剂量区。５°水平共线成角及０°水平重叠０５ｃｍ衔接时未见明显的低剂量区，但衔接处组织受量增加，ＤＴ２３Ｇｙ以上受照体积分别为（２４.０５±９.０３）ｃｍ３和（４４.７±８.２３）ｃｍ^３，差异有统计学意义（Ｐ＜０.０５）。结论　对于早期初治鼻咽癌常规放疗时，面颈联合野与下颈锁骨上单前野衔接移位方案较常规衔接方案可以明显改善衔接处剂量分布。上后颈电子线照射野与面颈缩野衔接时推荐采用５°水平共线成角照射。

Dosimetric evaluation for designed neighboring portals plans in conventional radiotherapy for patients with early nasopharyngeal carcinoma

Objective To evaluate the dosimetry of devised neighboring portals plans in conventional radiotherapy for patients with early nasopharyngeal carcinoma,and the value of clinical practice by using three dimensional treatment planning system.Methods Five patients with early untreated NPC were selected.Plan of junction moving was designed in joint of bilateral facial-cervical fields and low neck-supraclavicular field,which was that mathline of the two fields moved 1.5cm toward head with fields reaching half of irradiated dose,and the two fields given remaining dose of DT 19Gy/10f and Dm 25Gy/10f.When posterocervical triangular field irradiated by electric beam matched decreased facial-cervical fields,two designed joint plans included 5° horizontal（95° and 265°）matching no gap,and 0° horizontal matching the two joint fields overlapping about 0.5cm.Dose of the two fields was 20Gy/10f.Three dimensional treatment planning system was used to compare dosimetry of the designed plans and conventional plans.Results（1）Maximal dose and volume of above DT 52Gy in irradiated joint tissue of junction moving plan were DT 52.82±1.3Gy and 2.13±4.16cm^3.While the conventional matching plan were DT 56.27±1.81Gy and 12.49±8.29cm^3 respectively.Statistical difference was found between the two plans（P〈0.05）.（2）When posterocervical triangular field matched decreased facial-cervical fields,low dose volume was found in joint tissue using conventional 0° horizontal matching with no gap.While using 5° horizontal with no gap matching and 0° horizontal mathing with overlapping 0.5cm,it was not found.Volume-dose in irradiated joint tissue increased instead,of which above DT 23Gy were 24.05±9.03cm^3,44.7±8.23cm^3 respectively（P〈0.05）.Conclusion Comparing with conventional joint in matching bilateral facial-cervical fields and low neck-supraclavicular field,it is found that junction moving plan could obviously improve dose distribution of joint tissue.5° horizontal with no gap matching was recommended in matching posterocervical triangular field and decreased facial-cervical fields.