Department of Radiation Oncology, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, PR China.
J Radiat Res. 2012 Nov 1;53(6):954-60. doi: 10.1093/jrr/rrs041. Epub 2012 Jul 26.
This prospective study was to assess interfractional and intrafractional errors and to estimate appropriate margins for planning target volume (PTV) by using daily cone-beam computed tomography (CBCT) guidance in nasopharyngeal carcinoma (NPC). Daily pretreatment and post-treatment CBCT scans were acquired separately after initial patient setup and after the completion of each treatment fraction in 10 patients treated with IMRT. Online corrections were made before treatment if any translational setup error was found. Interfractional and intrafractional errors were recorded in the right-left (RL), superior-inferior (SI) and anterior-posterior (AP) directions. For the translational shifts, interfractional errors >2 mm occurred in 21.7% of measurements in the RL direction, 12.7% in the SI direction and 34.1% in the AP direction, respectively. Online correction resulted in 100% of residual errors ≤2 mm in the RL and SI directions, and 95.5% of residual errors ≤2 mm in the AP direction. No residual errors >3 mm occurred in the three directions. For the rotational shifts, a significant reduction was found in the magnitudes of residual errors compared with those of interfractional errors. A margin of 4.9 mm, 4.0 mm and 6.3 mm was required in the RL, SI and AP directions, respectively, when daily CBCT scans were not performed. With daily CBCT, the margins were reduced to 1.2 mm in all directions. In conclusion, daily CBCT guidance is an effective modality to improve the accuracy of IMRT for NPC. The online correction could result in a 70-81% reduction in margin size.
本前瞻性研究旨在评估鼻咽癌患者调强放疗中应用锥形束 CT （CBCT）引导每日摆位误差和分次内误差，并估计计划靶区（PTV）的合适边界。10 例接受调强放疗的患者在初始摆位后和每分次治疗结束后分别进行每日治疗前和治疗后锥形束 CT 扫描。如果发现任何平移摆位误差，则在治疗前进行在线校正。记录左右（RL）、上下（SI）和前后（AP）方向的分次间和分次内误差。对于平移误差，RL 方向、SI 方向和 AP 方向分别有 21.7%、12.7%和 34.1%的测量值存在>2mm 的分次间误差。在线校正后，RL 和 SI 方向的残余误差均为 100%≤2mm，AP 方向的残余误差为 95.5%≤2mm。三个方向均未出现残余误差>3mm。对于旋转误差，与分次间误差相比，残余误差的幅度显著减小。如果不进行每日 CBCT 扫描，则 RL、SI 和 AP 方向需要分别为 4.9mm、4.0mm 和 6.3mm 的边界。每日 CBCT 扫描后，边界缩小到所有方向的 1.2mm。总之，每日 CBCT 引导是提高鼻咽癌调强放疗准确性的有效方法。在线校正可使边界大小减少 70-81%。
