鼻咽癌放射治疗射野衔接设计的探讨

A Bi-isocentric Irradiation Technique in Radiotherapy for Nasopharyngeal Carcinoma

背景与目的:放射治疗鼻咽癌,面颈联合野已作为标准的射野设计,用一个颈部等中心半束照接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,本研究试图就鼻咽癌放射治疗中面颈联合野与颈部切线野最合适的射野衔接设计作一些探讨。方法:分别用两种方法设野,一种方法用一个等中心,半束照射面颈联合野与颈部切线照射,另一种用两个等中心,面颈联合野用鼻咽等中心照射,选用适当的楔形角,床转一定的角度,下颈切线照射再用颈部等中心半束照。比较两种设野衔接的区别。结果:根据治疗计划系统(treatmentplanningsystem,TPS)计算,两种设计的面颈联合野与颈部切线野之间的剂量衔接处都无冷点热点。用两个等中心设计的面颈联合野与颈部切线野,面颈联合野加角头足方向楔形板和床转一定的角度,其剂量分布比单一中心设野更均匀,更合理。99%的等剂量线包容颅底及鼻咽处大体肿瘤体积(grosstumorvolume,GTV)时,下颈及口咽部最高点剂量为103%,而且高剂量区容积也小,而用单一等中心设野时,如果要使95%的等剂量线包含颅底及鼻咽处GTV时,最高点处剂量达120%以上。结论:用两个等中心设计面颈联合野和颈部切线照,比单一颈部等中心设野时,接野处可以达到与单一等中心相同的结果,即不产生冷点及热点,而且三维TPS显示比单一等中心更合理、更均匀。

BACKGROUND ＆ OBJECTIVE. Although the problem of fields gap in radiotherapy for nasopharyngeal carcinoma （NPC） was solved by mono-isocentric technique, the dose distribution was heterogeneous with ＂hot＂ and/or ＂cold＂ spots. This study was to explore the best way to solve the problems of both fields gap and dose distribution using bi-isocentric technique. METHODS. Mono-isocentric and bi-isocentric irradiation techniques were used to simulate irradiation, respectively. Mono-isocentric irradiation technique was used to design the beam-split facio-upper neck field and the tangential low neck-supraclavicular field at the match plane. Biisocentric irradiation technique was used to design the facio-upper neck field and the tangential low neck-supraclavicular field at the match plane, namely the upper border of the tangential field and the lower border of the facioupper neck fields. RESULTS. Both mono-isocentric and bi-isocentric irradiation techniques were conformed well to QA at the junction of the neighboring portals, without ＂hot＂ or ＂cold＂ spots, by dosimetry. But the CADplan Three Dimensions Treatment Planning System showed that the dose distributional uniformity of sagittal plane in nasopharynx was much better in bi-isocentric technique than in mono-isocentric irradiation technique, without cold region in gross tumor volume （GTV） and/or hot region in normal tissue. CONCLUSIONS. Bi-isocentric irradiation technique takes a perfect matchplane and a satisfied dose distributional uniformity.