千伏级锥形束断层扫描在鼻咽癌适形调强放射治疗中的初步应用

Preliminary Application of Kilo-volt Cone-beam Computed Tomography to Intensity-modulated Radiotherapy of Nasopharyngeal Carcinoma

背景与目的:调强放射治疗(intensity-modulated radiotherapy,IMRT)由于剂量分布较常规放疗更符合鼻咽癌病灶与临近解剖结构对剂量的复杂要求而逐渐被临床采用,但IMRT对摆位精确度及其验证的要求高。千伏级锥形束断层扫描(kilo-volt cone-beam computed tomography,kV-CBCT)是新出现的实时图像引导技术,本研究旨在评价kV-CBCT图像引导技术在鼻咽癌调强放射治疗摆位修正中的应用价值。方法:应用kV-CBCT于放疗实施前对22例鼻咽癌患者进行扫描,并在线将重建的容积图像与计划CT扫描图像匹配,调整床位后给予放疗。对患者数据离线后进行分析,计算摆位误差以及计划靶体积(planning target volume,PTV)边界。结果:22例患者共754次kV-CBCT扫描中,首次kV-CBCT(调整前)扫描共505次,其中摆位偏差在左右、头足和前后3个方向误差≤2mm的检测次数分别为386(76.4%)、384(76.0%)和433(85.7%);调整床位后(调整后)扫描共106次,其中在3个方向摆位偏差≤2mm的检测次数分别为:103(97.2%)、103(97.2%)和106(100%);治疗后扫描共143次,3个方向误差≤2mm的检测次数分别为125(87.4%)、124(86.7%)和129(90.0%)。患者摆位的系统和随机误差调整前在X、Y、Z轴分别为(-0.7±1.6)mm、(-0.7±1.8)mm和(-0.3±1.7)mm,调整后分别为(-0.4±0.8)mm、(0.3±0.8)mm和(0.0±0.7)mm,治疗后分别为(0.2±1.2)mm、(0.3±1.3)mm和(0.1±1.1)mm。在调整前、后PTV最大边界分别为4.0mm和2.1mm。结论:kV-CBCT图像引导放射治疗在鼻咽癌IMRT中可以提高等中心摆位精度,检测并调整摆位误差,有效减小照射野边界。

BACKGROUND ＆ OBJECTIVE. The intensity-modulated radiotherapy （IMRT） with its highly conformed dose distribution to nasopharyngeal cancer （NPC） and the surrounding critical organs is being accepted increasingly in clinical practice. Due to the steep dose fall-offs of IMRT at the target margin, precise patient positioning and verification are required. This study was to evaluate the role of kilo-volt cone-beam computed tomography （kV-CBCT） in guiding the accurate positioning of IMRT for NPC. METHODS, kV-CBCT was performed on 22 NPCpatients before radiotherapy. The acquired CBCT were co-registered with the planning CT for online set-up correction and offline planning target volume （PTV） analysis. RESULTS, The 22 patients received a total of 754 kV-CBCT scans. Among the 505 scans before couch correction, the detection rates of deviation of ~〈2 mm were 76.4% in left-to-right （X） direction, 76.0% in superior-to-inferior （Y） direction, and 85.7% in anterior-to-posterior （Z） direction; among the 106 scans after correction, the detection rates were 97.2%, 97.2%, and 100% in X, Y and Z directions, respectively; among the 143 scans after treatment, the detection rates were 87.4%, 87.6%, and 90.0%, respectively. The overall setup errors in X, Y and Z directions were （-0.7±1.6） mm, （-0.7±1.8） mm and （-0.3±1.7） mm, respectively, before correction; （-0.4±0.8） mm, （0.3±0.8） mm and （0.0±0.7） mm, respectively, after correction; （0.2±1.2） mm, （0.3±1.3） mm and （0.1±1.1） mm, respectively, after treatment. The maximal PTV margin was 4.0 mm before correction and 2.1 mm after correction. CONCLUSION. kV-CBCT image-guided radiotherapy may improve the set-up precision of IMRT for NPC.