鼻咽癌调强放疗布野方案剂量学比较

Dosimetric Comparison of Intensity Modulated Radiation Therapy Plans for Nasopharynx Carcinoma

目的:通过对鼻咽癌逆向调强放疗三种常用的7野方案进行比较,确定符合临床要求的较佳布野方案。方法:对10例初治鼻咽癌患者采用调强放射治疗方案,针对每例患者按不同方案设计3个计划,分别为方案A:7野均匀分布,方案B:前7野,方案C:后7野。每野的照射范围从颅底到锁骨上淋巴预防区。所有计划都用同样的物理目标函数和约束条件进行优化,分别比较三个计划的靶区和危及器官剂量分布、剂量体积直方图(DVH)、靶区适形度指数(CI)等指标。结果:三个计划的靶区剂量分布无明显差异,方案A、C比方案B降低了口腔黏膜平均剂量的21.2%和31.3%,但是方案C计划增加了后颈部软组织的剂量。方案A、B比方案C分别降低了颞叶D5剂量的2.7%、3.5%和脑干D5剂量的1.7%、2.3%。A、B、C三种方案中脑干、脊髓的D1剂量无明显差别,腮腺、颞颌关节的D50剂量也无明显差别。适形度指数三种方案差别并不显著。结论:调强放疗7野计划可以满足鼻咽癌靶区的剂量要求。布野方向对剂量分布有较大影响,方案A优于方案B、C;但是若肿瘤侵犯到了鼻咽腔的顶壁、前床突、后床突等部位,方案A、C较难避开晶体,只能选择B方案,用非共面射野方式以避开晶体。

Objective： To fred the optimal beam arrangement for nasopharynx carcinoma treatment with intensity modulated radiation therapy （IMRT） technique through comparisons of three different beam arrangements. Methods： Three IMRT plans were designed for each of 10 patients with Nasopharynx Carcinoma. Plan A： seven equispaced fields; Plan B： anterior seven fields; Plan C： hind seven fields. The area of each field was from skullbase to supra clavicular lymph node area. We used the same condition to optimize all the plans.We compared the dose distribution, dose volume histograph （DVH） and conformity index of the three different beam arrangements. Results： There was little difference in target＇s coverage among all plans. Plan A and plan C respectively showed 21.2% and 31.3% decrease of mean dose to the oral mucosal as compared with plan B,but plan C with an increase in dose to the neck. There were not obvious differences in D1 to brain stem, spinal cord and D50 to parotid glands, temporomandibular joints （TMJS） among the three plans. Plan A and plan C respectively showed 2.7% .3.5% decrease of D5 to the temporal lobe and 1.7% ,2.3% decrease of D5 to the brain stem as compared with plan B. There was also little difference in the dose distribution and conformity to the target among the three plans. Conclusions： Intensity modulated radiation therapy （IMRT） with seven fields is able to provide desirable dose distribution for Nasopharynx Carcinoma. Different beam arrangements have great effects on the dose distribution. Plan A is superior to plan B and plan C. But we must choose plan B to avoid lens when the tumor infi＇inged the coping of the nasopharynx antrum ,anterior clinoid process,posterior clinoid process etc.