直线加速器二级准直器在鼻咽癌调强放疗计划设计中的应用研究

Application of liner-accelerator two-degrade collimator in the treatment of nasopharyngeal carcinom with intensity-modulated radiotherapy

目的 制定鼻咽癌调强放疗计划时,通过控制直线加速器二级准直器的位置及角度以达到更好地限制头颈部危及器官的受照剂量.方法 应用Eclipse计划系统针对10例鼻咽癌患者分别制定T1、T2模式调强放疗计划.T1模式采用0°、52°、106°、160°、212°、258°、308°方向射野,二级准直器位置及角度不做限制,设置优化参数进行剂量运算.T2模式保持射野方向和优化参数与T1相同,根据每个计划实际情况适当修正射野二级准直器位置和角度,然后进行剂量运算.通过剂量体积直方图比较两种模式下计划的计划靶体积和危及器官剂量分布.结果 T1、T2模式调强放疗计划的计划靶体积均满足剂量要求,适形指数分别为0.82、0.83（t=-0.25,P=0.815）.危及器官中晶状体、眼球、视神经和角膜的最大剂量分别降低28.7%（t=4.80,P=0.000）、2.7%（t=2.99,P=0.021）、1. 4%（t=1.05,P=0.032）和30.5%（t=2.99,P=0.020）,腮腺平均受量和V35增加0.6%和9.9%（t=-2.82,P=0.043;t=-2.05,P=0.038）.结论 与T1模式相比,适当控制二级准直器的位置和角度能更好减少散射线及漏射线对眼球特别是晶状体的影响,但会略增加腮腺受量.

Objective To study the efficacy of using multileaf collimators with different position and different degree in the treatment of nasopharyngeal carcinoma （NPC） using intensity-modulated radiotherapy techniques. Methods Ten patients with NPC were administered and analyzed. The penumbra characteristics, dose of target, and radiation conformal indexes （CI） of mode T1 and mode T2 were measured and compared using dose volume histogram generated by Varian Eclipse three-dimensional planning computer system. Mode T1 ：The angles of seven coplanar beams were 0°, 52°, 106°, 160°, 212°, 258°and 308°,respectively. There were no restriction on the position and degree of multileaf collimators. Parameters were set and optimized. Mode T2 ：The beam angles and the parameters were as same as mode T1. According to the actual situations, the position and the degree of the multileaf collimators were changed. Then thedose optimization was performed. Results Target dose coverage in both mode T1 and T2 could be clinically accepted, and the CI were 0. 82 and 0. 83（t = -0. 25, P =0. 815）. The maximum dose reductions in the lens, eyes, optic nerves and corneas were 28. 7% （t = 4. 80, P = 0. 000）, 2. 7% （t = 2. 99, P = 0. 021）,1.4%（t= 1.05,P=0.032）, and 30.5% （t=2.99,P=0. 020）, respectively. However, the mean dose and V35 of the parotid were increased by 0. 6% （t = - 2. 82, P = 0. 043） and 9.9% （t = - 2. 05, P =0. 038）. Conclusions Opimization of multileaf collimators can reduce the scattering and leaking rays. Compared with mode T1 ,controlling the position and degree of multileaf collimators could reduce the radiation dose to the eyes and optic-nerves, especially to the lens.