鼻咽癌逆向调强计划中照射野方向和照射野数目对剂量分布的影响  

Influence on dose distribution by beam direction and beam number in inverse intensity-modulated for nasopharyngeal carcinoma

作　　者：常熙[1] 徐志勇[1] 周莉钧[1] 王孝深[1] 朱骥[1] 胡超苏[1] 傅小龙[1] 

机构地区：[1]复旦大学附属肿瘤医院放疗科

出　　处：《中国癌症杂志》2007年第4期324-328,共5页China Oncology

摘　　要：背景与目的:调强放疗技术正逐步应用于鼻咽癌的治疗。对于鼻咽癌这种对放疗技术要求最为复杂的头颈部肿瘤,制定IMRT计划是一个费时费力的过程,有许多物理参数会影响到剂量分布,其中照射野方向和数目的选择又是一个需要反复实验的过程。本研究以鼻咽癌为例着重探讨射野方向和数目对IMRT计划剂量分布的影响,为制定鼻咽癌IMRT计划提供一些参考,可以减少优化中反复实验所需要的时间。方法:选择临床常见的早期鼻咽癌10例、局部晚期鼻咽癌10例,对每个病例分别制定9野、7野调强放疗计划,7野计划有A、B两种不同的线束入射角度方案,同一病例的7野、9野计划均应用相同的物理目标函数。将7野A组和B组做比较以优化射野方向,较优的一组再与9野计划做比较以优化照射野数目;用靶区覆盖度,靶区均匀性、靶区适形度、机器跳数,子野数目等物理参数作为计划评价指标。结果:对于早期病例,7野A组、B组和9野计划均能满足要求,两种计划的靶区覆盖度、靶区均匀性及靶区适形度的差别不大,7野A组中机器跳数、子野数均低于B组;对于晚期病例,虽然9野计划中机器跳数尤其是子野数都劣于7野A组及B组计划,但9野计划在靶区覆盖度明显优于7野计划。结论:照射野方向和照射野的数目对剂量分布有影响,增加照射野的数目可以改善体积较大的病灶的剂量分布。对病灶体积大的肿瘤,9野计划比7野的优势明显。综合考虑物理及生物效应,建议对于早期病例7野计划可基本解决问题,对局部晚期病例,9野方案较为可靠。Background and purpose： Intensity-modulated radiation therapy （IMRT） is now widely used in the treatment of nasophyngeal carcinoma（ NPC）. How to optimize treatment planning is the most challenging problem in the clinic in terms of dosimetry due to the complicated anatomy. Dose distribution will be influenced by many physical parameters including beam number and beam direction and the optimization process could be very time-consuming. This study was to evaluate the influence of different beam number and beam angle on dose distrihution in the treatment of NPC by IMRT and hopefully to set up the baste points on how to plan IMRT with shorter time than hefore. Methods： 20 NPC patients with early stage（10） and locally advanced stage（10） were selected . IMRT treatment plan with seven beams and nine beams were formulated tbr every patient. Two beam angulus incidentiae （ A, B groups） for seven beams plan were designed. The same physical objective function was applied tot the same patient and both groups . We compared seven beams plan with different beam angulus incidentiae to optimize beam angle, and then seven beams plan with the preferable angle is compared with nine beam plan to optimize beam number. Plans were evaluated in terms of target coverage, larget dose uniformity, target conformability, monitor unit and segment numbers. Results： In the patients with early stage NPC.all parameters were met in both seven beams plans and nine beams plans, hut MUs and segment number were fewer in group A than those in group B. In the patients with locally advanced stage NPC, although MUs and segment number were fewer in gruup A and group B than those in nine beams plans, target dose coverage and target dose uniformity in nine beams plans were superior to those in seven beams plans. Conclusions： The beam angle and the number of beams have influence upon dose distribution, the dose distribution would be improved for large volume target with the inctwnent of heam number. Taking therapeutic index （TCP/NTC

关 键 词：鼻咽癌 放射治疗 逆向调强放疗计划 照射野方向 照射野数目 

分 类 号：R739.6[医药卫生—肿瘤]