摘要
目的 探讨CBCT获得的摆位误差对脑干剂量影响.方法 局部晚期鼻咽癌患者4例行3DRT并获取在线摆位误差,计划33次放疗,脑干最高总量限量〈54 Gy,脑干单次最高限量为163.6 cGy.将原计划中心点根据摆位误差进行偏移,带入原计划重新运算.每位患者单次治疗后记录脑干每一层面〉163.6 cGy区域.再通过CORELDRAW软件将同一脑干层面超剂量区域进行叠加,用Photoshop软件统计超剂量区域.记录患者放疗前体重变化.配对样本t检验差异.结果 未经校正的116次CBCT在x、y、z方向和床角上的误差分别为（0.90±0.85）、（0.98±0.6）、（0.98±1.05）mm和0.25°±0.49°.116次CBCT共获取2502层脑干图像,其中2040层脑干剂量不同程度超过最高限量;其中1例患者脑干超剂量次数最多,20次以上的总体积达3.83%;1例患者脑干超剂量体积仅占总体积的0.13%.体重减少和摆位误差之间无相关性（P〉0.05）.结论 CBCT获得的摆位误差对脑干剂量有明显影响,它是一种有效的验证手段,对勾画靶区具有指导意义.
Objective To investigate the effects of setup error acquired by cone-beam computed tomography （ CBCT） on the dose to the brainstem. Methods Setup errors were collected from 4 patients with locally advanced nasopharyngeal carcinoma （ NPC） undergoing three-dimensional radiotherapy. In the 33 radiotherapy plans, the upper limit of the dose to the brainstem was 54 Gy in total radiation and 163. 3 cGy in a single radiation. Treatment was re-planed using a corrected center based on setup error. For each patient, areas exposed to radiation higher than 163. 64 cGy were recorded in each layer of the brainstem after single treatment. The CorelDraw software was used to superpose all overdose areas in each layer of the brainstem. The Photoshop software was used to calculate the volume of the overdose areas. The changes in weight after radiotherapy were recorded and analyzed using paired t test. Results In 116 CBCT scans without correction, the setup errors were （0.90±0. 85）,（0.98±0. 6）, and （0.98±1. 05） mm in x, y, and z directions, and （0.25±0. 49）° in rotation. According to the images of a total of 2502 layers of the brainstem acquired by 116 CBCT scans, 2040 layers of the brainstem had doses over the upper limit to different degrees. The patient with the highest frequency of overdose in the brainstem had a total overdose volume up to 3. 83% in 20 scans. Another patient had the overdose volume only 0. 13% of the total volume. There was no significant relationship between weight loss and setup error （ P〉0. 05 ） . Conclusions Setup error acquired by CBCT has a substantial impact on the dose to the brainstem. It is an effective approach for verification of target volume delineation.
出处
《中华放射肿瘤学杂志》
CSCD
北大核心
2016年第12期1331-1334,共4页
Chinese Journal of Radiation Oncology
基金
湖南省科技计划项目（2011SK3220）
