鼻咽癌调强放疗射野方向对急性放疗反应的影响

Effect of Beam Orientation on Acute Complications in Intensity-modulated Radiation Therapy of Nasopharyngeal Carcinoma

目的:比较两种不同射野方案的鼻咽癌调强计划及其导致的急性放疗反应,确定出一种合理的射野方案。方法:随机选20例鼻咽癌患者,应用飞利浦Pinnacle 8.0计划系统进行设计。其中10例患者采用IMRT-7P方案进行治疗,即调强放疗(IMRT)7野后半平面的均分布野方案;另10例患者采用IMRT-7A方案,即IMRT7野均分的布野方案。再分别模拟出对应的后半平面野和均分野计划,进行剂量学比较。比较参数为计划靶区的覆盖、均匀指数(HI)和适形指数(CI)以及危及器官(OARs)。观察并比较两组患者急性放疗反应。结果:两组计划具有相似的靶区覆盖、HI和CI,IMRT-7P对保护脑干、脊髓、腮腺和颌下腺,具有一定的优势(P<0.05),特别是保护了口腔。口腔的D_(MEAN):(29.3±1.3)Gy,(35.7±2.3)Gy,P<0.01;V_(30):(36.2±5.4)%,(73.1±10.9)%,P<0.01;V_(40):(13.3±3.8)%,(29.0±9.7)%,P<0.01。IMRT-7P所治疗的患者在口干、口腔黏膜炎、皮肤损伤和体质量下降上急性放疗反应更轻(P<0.05)。结论:鼻咽癌IMRT-7P治疗方案能一定程度上减少危及器官的剂量,更好的保护危及器官,减轻了急性放疗反应。

Objective： The aim of this study was to compare two different beam arrangements in the treatment plan of intensi- ty-modulated radiation therapy （IMRT） for nasopharyngeal carcinoma （NPC） and its acute complications to find a reasonable beam arrangement. Methods： Twenty NPC patients were randomly selected in the study. Philips Pinnacle Planning System 8.0 was chosen to design the IMRT plan. Ten of the 20 patients were treated by the IMRT-7P plan, which was planned by the hind half-planes of seven fields of the IMRT plan. The remaining 10 patients were treated by the IMRT-7A plan, which was planned by seven equi-spaced fields of the IMRT plan. Then, the plans of homologous hind half-plane and equi-spaced fields were re-planned. Dosimetric comparisons between IMRT-7P and IMRT-7A were conducted to evaluate the coverage, homogeneity index （HI）, and conformity indexes （CI） of the planning target volume （PTV） and organs at risk sparing （OARs）. Acute complications of the patients in the two groups were observed and compared during radiotherapy. Results： IMRT-7P and IMRT-7A had a similar PTV coverage. No significant differences in HI and CI between IMRT-7A and IMRT-7P were observed. However, in the aspect of OARs, IMRT-7P had a better sparing effect on the brain stem, cord, parotid gland, and sub-mandibular gland （P〈0.05） to a certain extent, especially on oral cavity where IMRT-7P plan had significantly lower pertinent parameters compared with that of IMRT-7A [DMEAN：（29.3± 1.3） Gy, and （35.7±2.3） Gy, P〈0.01; V30：（36.2± 5.4）%, and （73.1±10.9）%, P〈0.01; V40：（13.3±3.8）%, and （29.0±9.7）%, P〈0.01]. In the aspect of acute complications, such as xerostomia, acute oral mucositis, skin injury, and weight loss, patients who were treated by IMRT-7P achieved a better curative effect compared with those treated by IMRT-7A （P〈0.05）. Conclusion： IMRT-7P plan for NPC can reduce the dose delivered to OARs to a certain extent and can better protect the normal tissue around the target. In addition, the IMRT-7P plan can better relieve acute complications of radiotherapy compared with the IMRT-7A plan.