Department of Radiation Oncology, David of Geffen School of Medicine at UCLA, Los Angeles, California, USA.
Int J Radiat Oncol Biol Phys. 2013 Jul 1;86(3):432-9. doi: 10.1016/j.ijrobp.2013.01.022. Epub 2013 Mar 6.
Various image guidance systems are commonly used in conjunction with intensity modulated radiation therapy (IMRT) in head-and-neck cancer irradiation. The purpose of this study was to assess interfraction patient setup variations for 3 computed tomography (CT)-based on-board image guided radiation therapy (IGRT) modalities.
A total of 3302 CT scans for 117 patients, including 53 patients receiving megavoltage cone-beam CT (MVCBCT), 29 receiving kilovoltage cone-beam CT (KVCBCT), and 35 receiving megavoltage fan-beam CT (MVFBCT), were retrospectively analyzed. The daily variations in the mediolateral (ML), craniocaudal (CC), and anteroposterior (AP) dimensions were measured. The clinical target volume-to-planned target volume (CTV-to-PTV) margins were calculated using 2.5Σ + 0.7 σ, where Σ and σ were systematic and random positioning errors, respectively. Various patient characteristics for the MVCBCT group, including weight, weight loss, tumor location, and initial body mass index, were analyzed to determine their possible correlation with daily patient setup.
The average interfraction displacements (± standard deviation) in the ML, CC, and AP directions were 0.5 ± 1.5, -0.3 ± 2.0, and 0.3 ± 1.7 mm (KVCBCT); 0.2 ± 1.9, -0.2 ± 2.4, and 0.0 ± 1.7 mm (MVFBCT); and 0.0 ± 1.8, 0.5 ± 1.7, and 0.8 ± 3.0 mm (MVCBCT). The day-to-day random errors for KVCBCT, MVFBCT, and MVCBCT were 1.4-1.6, 1.7, and 2.0-2.1 mm. The interobserver variations were 0.8, 1.1, and 0.7 mm (MVCBCT); 0.5, 0.4, and 0.8 mm (MVFBCT); and 0.5, 0.4, and 0.6 mm (KVCBCT) in the ML, CC, and AP directions, respectively. The maximal calculated uniform CTV-to-PTV margins were 5.6, 6.9, and 8.9 mm for KVCBCT, MVFBCT, and MVCBCT, respectively. For the evaluated patient characteristics, the calculated margins for different patient parameters appeared to differ; analysis of variance (ANOVA) and/or t test analysis found no statistically significant setup difference in any direction.
Daily random setup errors and CTV-to-PTV margins for treatment of head-and-neck cancer were affected by imaging quality. Our data indicated that larger margins were associated with MVFBCT and MVCBCT, compared with smaller margins for KVCBCT. IGRT modalities with better image quality are encouraged in clinical practice.
在头颈部癌症放射治疗中，各种图像引导系统通常与调强放疗（IMRT）联合使用。本研究旨在评估三种基于计算机断层扫描（CT）的在线图像引导放疗（IGRT）模式的分次间患者摆位变化。
回顾性分析了 117 名患者的 3302 次 CT 扫描，包括 53 名接受兆伏锥形束 CT（MVCBCT）、29 名接受千伏锥形束 CT（KVCBCT）和 35 名接受兆伏扇形束 CT（MVFBCT）的患者。测量了正中矢状面（ML）、颅尾（CC）和前后（AP）方向的每日变化。使用 2.5Σ+0.7σ计算临床靶区到计划靶区（CTV-to-PTV）的边界，其中Σ和σ分别为系统和随机定位误差。分析了 MVCBCT 组的各种患者特征，包括体重、体重减轻、肿瘤位置和初始体重指数，以确定它们与每日患者摆位的可能相关性。
ML、CC 和 AP 方向的平均分次间位移（平均值±标准差）分别为 0.5±1.5、-0.3±2.0 和 0.3±1.7mm（KVCBCT）；0.2±1.9、-0.2±2.4 和 0.0±1.7mm（MVFBCT）；0.0±1.8、0.5±1.7 和 0.8±3.0mm（MVCBCT）。KVCBCT、MVFBCT 和 MVCBCT 的日随机误差分别为 1.4-1.6、1.7 和 2.0-2.1mm。在 ML、CC 和 AP 方向上，观察者间的变异分别为 0.8、1.1 和 0.7mm（MVCBCT）；0.5、0.4 和 0.8mm（MVFBCT）；0.5、0.4 和 0.6mm（KVCBCT）。KVCBCT、MVFBCT 和 MVCBCT 的计算最大均匀 CTV-to-PTV 边界分别为 5.6、6.9 和 8.9mm。对于评估的患者特征，不同患者参数的计算边界似乎不同；方差分析（ANOVA）和/或 t 检验分析发现，任何方向均无统计学显著的摆位差异。
头颈部癌症治疗的每日随机摆位误差和 CTV-to-PTV 边界受成像质量的影响。我们的数据表明，与 KVCBCT 相比，MVFBCT 和 MVCBCT 的边界更大。在临床实践中鼓励使用图像质量更好的 IGRT 模式。
