头颈肿瘤立体定向分次照射靶区定位的误差分析

背景与目的:明确靶区定位的精确度是立体定向分次照射质量保证的基本要求。本文主要分析头颈肿瘤立体定向分次照射(fractionatedstereotacticradiotherapy,FSRT)中机械等中心、CT定位、治疗摆位以及CT图像误差等可能引起的靶区定位误差。方法:使用立体定向治疗计划系统、靶点模拟器、头部定位框架检查各个治疗阶段靶区定位的误差。设置任意5个参考点,使用靶点模拟器检查CT定位误差;选取7个不同机器臂架/治疗床角度,定期用胶片检验使用的PhilipsSL-18直线加速器等中心误差大小;用验证片检查治疗摆位误差;对自制模体行CT扫描,分析CT图像伪影可能引起的图像误差。结果:CT定位误差约为(1.5±0.4)mm;在检查的不同机器臂架/治疗床角度中机械等中心最大误差为(1.0±0.6)mm;患者摆位的距离误差为(1.0±0.3)mm;整个治疗过程中靶区定位误差约为(2.1±0.8)mm。结论:立体定向分次照射中需要综合考虑各个阶段中可能对治疗靶区定位产生的影响,误差分析结果可用来确定治疗的计划靶区。

Analysis of target localization errors in fractionated stereotactic radiotherapy for head and neck carcinoma

BACKGROUND & OBJECTIVE: Accurate target localization is the essential requirement in the quality control in fractionated stereotactic radiotherapy (FSRT). This paper is to analyze the magnitude of errors in FSRT for head and neck carcinoma including the errors of CT localization, mechanical isocenter, setup of patients, and CT image. METHODS: The stereotactic radiotherapy treatment planning system (SRT-TPS), target simulator and head frame were used to check the errors of target localization during each radiation procedure. Five reference points were set randomly; the CT localization error was measured using the target simulator. Seven different mechanical angles of Gantry/Table were selected; the magnitude of isocentric errors of Philips SL-18 linear accelerator were acquired with films. Setup errors were collected by portal films. The image error possibly from CT image artifact was analyzed after scanning a self-made phantom by CT. RESULTS: The CT localization error was(1.5+/-0.4)mm.The maximal error of the mechanical isocenter was (1.0+/-0.6)mm according to the different mechanical gantry/table angles. The distance error of patient setup was (1.0+/-0.3)mm. The maximal total errors estimate was (2.1+/-0.8)mm. CONCLUSIONS: The effect of target localization of every procedure should be taken in account in FSRT, the results of the error analysis can be used to determinate the planning target volume in the treatment.