Xia Shi-An, Zhang Song-Fang, Tu Yong-Qing, Wu Guo-Hua, Lin Qing, Yao Yuan
Department of Radiation Oncology, Xinhua Hospital, Shanghai Second Medical University, Shanghai 200092, P. R. China.
Ai Zheng. 2006 Jan;25(1):119-21.
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.
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. Bi-isocentric 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 facio-upper neck fields.
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.
Bi-isocentric irradiation technique takes a perfect match-plane and a satisfied dose distributional uniformity.
虽然鼻咽癌（NPC）放疗中的射野衔接问题已通过单等中心技术得到解决，但剂量分布仍存在“热点”和/或“冷点”的不均匀性。本研究旨在探索采用双等中心技术解决射野衔接和剂量分布问题的最佳方法。
分别采用单等中心和双等中心照射技术进行模拟照射。单等中心照射技术在匹配平面设计分野面颈上部野和切线野颈下部-锁骨上野。双等中心照射技术在匹配平面即切线野上缘和面颈上部野下缘设计面颈上部野和切线野颈下部-锁骨上野。
通过剂量学测量，单等中心和双等中心照射技术在相邻射野交界处均符合质量保证要求，无“热点”或“冷点”。但CADplan三维治疗计划系统显示，双等中心技术在鼻咽矢状面的剂量分布均匀性明显优于单等中心照射技术，大体肿瘤体积（GTV）内无冷区，正常组织内无热区。
双等中心照射技术具有完美的匹配平面和满意的剂量分布均匀性。
