早期鼻咽癌三维适形、常规和传统外照射计划的剂量学评价

Dosimetric Evaluation for Three Dimensional Conformal, Conventional, and Traditional Radiotherapy Plans for Patients with Early Nasopharyngeal Carcinoma

背景和目的:传统鼻咽癌外照射技术存在不少的缺陷,改进鼻咽癌外照射技术已成为提高鼻咽癌疗效的一个努力方向,本研究利用三维治疗计划系统对鼻咽癌传统、常规和三维适形放疗(3DCRT)计划作剂量学比较,评估采用不同方法的意义。方法:选择22例早期鼻咽癌患者,用三维治疗计划系统对每例患者分别作出传统、常规和3DCRT计划设计,然后根据靶区覆盖率(V95)、正常组织受量(D50,D33和D5等)和正常组织并发症发生率(NTCP)比较这三种计划。结果:剂量学比较表明,三种不同计划的PTVnx60和PTVnx50的V95分别为90.29%和77.67%(传统)、98.44%和98.85%(常规)、99.98%和99.63%(3DCRT),3DCRT和常规放疗有满意的V95,尤其是在亚临床病灶范围,两者均优于传统放疗;在正常组织保护方面,3DCRT和常规治疗计划均比传统方式能更好地保护脑干、颞叶、视交叉和垂体,而3DCRT比常规和传统方式更好地保护了腮腺和颞颌关节。结论:三种计划设计方式中,3DCRT和常规方法均有很好的V95,尤其是在亚临床病灶方面,而3DCRT治疗早期鼻咽癌的优势在于给予靶区特别是亚临床病灶区相同的剂量分布的前提下,可以比常规和传统方法减少某些正常组织器官如腮腺、颞颌关节等的照射剂量。

BACKGROUND &OBJECTIVE:Traditional external beam irradiation techniques for nasopharyngeal carcinoma have a lot of shortcomings, and improving external beam techniques have become an endeavor to enhance curative effectiveness. This study was designed to compare the dose distribution of three dimensional conformal radiotherapy (3D CRT) with traditional and conventional radiotherapy plans in the patients with early nasopharyngeal carcinoma using three dimensional treatment planning system. METHODS: Twenty two patients with early nasopharyngeal carcinoma were selected. Traditional, conventional, and 3D CRT plans were made for each of them and compared with respect to target coverage (V95), normal tissue sparing (D50, D33, and D5, etc), normal tissue complication probability (NTCP). RESULTS: Dosimetric comparison indicated that the V95 of PTVnx60 and PTVnx50 for three different plans were 90.29%and 77.67%(traditional), 98.44%and 98.85%(conventional), 99.98%and 99.63%(3D CRT), respectively; and both conventional and 3D CRT had satisfied dose coverage of target volume especially in subclinical lesion region compared with traditional radiotherapy. With respect to normal tissue sparing, 3D CRT and conventional treatment plans could spare more brainstem, temporal lobe, optic chiasm, and pituitary than traditional plans; and 3D CRT could spare more parotid gland and temporomandibular joint than traditional and conventional treatments. CONCLUSION: Considering the dose distribution of the three treatment plans, both conventional and 3D CRT had satisfied dose coverage of target volume especially in subclinical lesion region compared with traditional radiotherapy, and 3D CRT plans can spare more normal tissues such as parotid gland and temporomandibular joint etc, and decrease their NTCP while it get the same dose distribution in target volume as traditional and conventional plans do in the treatment of early nasopharyngeal carcinoma.