Peng Jiayuan, Chang Xi, Xu Zhiyong, Wang Jiazhou, Guan Xiyin, Cheng Lin, Zhang Zhen, Hu Weigang
Department of Radiation Oncology, Fudan University Shanghai Cancer Center, China.
Australas Phys Eng Sci Med. 2013 Jun;36(2):193-9. doi: 10.1007/s13246-013-0194-0. Epub 2013 May 2.
This study was designed to investigate the residual rotational error (RRE) of an X-ray volume imaging (XVI) system and evaluate the dosimetric impact of this error on spinal tumor radiation therapy. Various rotational displacements (set rotations) were applied to an anthropomorphic phantom placed on a HexaPod evo RT CouchTop (HexaPod couch). To detect these set rotations, a series of cone-beam computed tomography (CBCT) scans of the phantom were acquired and registered to the planning CT in the XVI system. The RRE of the XVI system was evaluated by comparing the difference between the set rotations and the registration results from the XVI. The error-introduced plans (by applying the RRE to the copies of the reference plan) were generated in the treatment planning system. The dose distribution was compared between the reference plan and the error-introduced plans to assess the dosimetric impact of RRE. The root-mean-square (RMS) of RREs were 0.31°, 0.35°, and 0.25° in the X (pitch), Y (roll), and Z (yaw) direction, respectively. For the reference plan versus the error-introduced plans, the PTV volumes receiving the prescribed dose (V 100) were 95.1 % versus 94.8-95.7 %; the conformity indices of the PTV were 1.17 versus 1.16-1.19; the minimum dose to 1 cc of volume (D1 cc) of spinal cord were 43.73 Gy versus 43.71-43.89 Gy; the left kidney volumes receiving 15 Gy (V 15) were 29.7 % versus 29.2-30.7 %; and the V 15 values of the right kidney were 26.1 % versus 24.6-27.5 %. Relative to the reference plan, the dose difference of error-introduced plans exceeded 3 % in kidney V 15. In conclusion, the XVI system can accurately detect the rotational displacement. However, large dose deviations were introduced by RREs when organs at risk were away from the iso-center even for small RREs.
本研究旨在调查X射线容积成像（XVI）系统的残余旋转误差（RRE），并评估该误差对脊柱肿瘤放射治疗的剂量学影响。对放置在六轴机器人evo RT治疗床面（六轴机器人治疗床）上的人体模型施加各种旋转位移（设定旋转）。为了检测这些设定旋转，对人体模型进行了一系列锥束计算机断层扫描（CBCT），并在XVI系统中与计划CT进行配准。通过比较设定旋转与XVI配准结果之间的差异来评估XVI系统的RRE。在治疗计划系统中生成误差引入计划（通过将RRE应用于参考计划的副本）。比较参考计划和误差引入计划之间的剂量分布，以评估RRE的剂量学影响。RRE在X（俯仰）、Y（横滚）和Z（偏航）方向的均方根（RMS）分别为0.31°、0.35°和0.25°。对于参考计划与误差引入计划，接受处方剂量（V100）的计划靶体积（PTV）分别为95.1%和94.8 - 95.7%；PTV的适形指数分别为1.17和1.16 - 1.19；脊髓1 cc体积的最小剂量（D1 cc）分别为43.73 Gy和43.71 - 43.89 Gy；接受15 Gy（V15）的左肾体积分别为29.7%和29.2 - 30.7%；右肾的V15值分别为26.1%和24.6 - 27.5%。相对于参考计划，误差引入计划在肾V15中的剂量差异超过3%。总之，XVI系统能够准确检测旋转位移。然而，即使对于小的RRE，当危及器官远离等中心时，RRE也会引入较大的剂量偏差。
