鼻咽癌放射治疗野中野设计的探讨

Exploring Field-in-Field Technique in 3DCRT Plan for Nasopharyngeal Cancer

背景与目的:鼻咽癌放射治疗,面颈联合野已作为标准的射野设计,用一个中心半束射野解决了面颈联合野与颈部切线野的衔接问题,但面颈联合野内存在剂量冷点与热点,剂量均匀性差。因此本研究希望就鼻咽癌放射治疗面颈联合野中进行野中野的设计作一些探讨。方法:在设计半束照射面颈联合野时,使野的下部最大剂量保持在105%左右,再在野的上部加射野的设计方案。结果:根据治疗计划系统(treatment planning system,TPS)计算,由于是一个中心的半束射野,面颈联合野与颈部切线野的衔接处无冷热点,在面颈联合野内加入野中野和颈部切线野,故比用两个中心设计的,面颈联合野与颈部切线野,技术员摆位更简单,更准确。其剂量分布比单一的面颈联合野更均匀,更合理。95%的等剂量线包容颅底及鼻咽处肿瘤体积(gross tumor volume,GTV)时,下颈及口咽部最高点剂量为105%左右,而且高剂量区容积也小。结论:用一个中心半束面颈联合野中野和颈部切线野方法照射,比单一面颈联合野照射时,剂量分布更均匀,更合理,比两个中心面颈联合野与颈部切线野照射时,技术员摆位更简单,衔接处的剂量更准确。

Objective：In the 3DCRT plan of nasopharyngeal cancer,face-neck-field has became a standard.The problem of fields gap between the face-neck-field and the tangential low eck-supraclavicular field was solved by mono-isocentric technique,however,the dose distribution within the face-neck-field was heterogeneous with ＂hot＂ and/or ＂cold＂ spots.This study is to explore a ＂field in field＂ technique in the design of face-neck-field in nasopharyngeal cancer.Methods：When designing beam-split face-neck-field,the hot spots in lower part should be less than 105%,and a small field will be added to the beam-split face-neck-field by ＂field in field＂ technique.Results：According to the calculation result of TPS,there are no ＂hot＂ and/or ＂cold＂ spots between the face-neck-field and the tangential low neck-supraclavicular field which is benefit from using the beam-split field with one isocenter.Adding small field and the tangential low neck-supraclavicular field to the face-neck-field lead to better dose distribution,95% isodose line covers the volume of the skull base and GTV,while the maximum dose in the lower neck and pharynx is about 105% of prescribed dose,the volume of high dose is also smaller.And the technique makes the setting up more easier and more accurate.Conclusions：The beam-split face-neck-field and the tangential low neck-supraclavicular field with mono-isocentric radiation technique makes the dose distribution more uniform and reasonable than single face-neck-field radiation technique.Also,setting up of the patient is more easier and the dose between fields gap is more accurate than bi-isocentric radiation technique.