Optical Surface Monitoring系统跟踪运动靶区的位置精度和剂量精度验证

Verification of the accuracy of localization and dose based on optical surface monitoring system for tracking moving targets

目的:评估Optical Surface Monitoring System(OSMS)测量靶区运动的几何精度和使用OSMS跟踪运动靶区放疗时的剂量精度。方法:①分别使用OSMS与锥形束CT监测腹部模体的位置,通过移动治疗床使模体产生位移和旋转,对比二者对模体位置的测量结果;②用呼吸运动平台搭载MatriXX二维电离室阵列,测量不同跟踪阈值时模体内相对剂量,分别与计划剂量分布对比,分析不同跟踪阈值时计划验证的gamma通过率。结果:OSMS和锥形束CT系统对模体平移和旋转预设偏移的测量结果差异很小,使用OSMS门控技术时OSMS的阈值越小gamma通过率越高,相对剂量分布与计划剂量的一致性也越好。结论:OSMS系统对模体表面位置监测精度高,可以应用到实际放射治疗的辅助摆位。使用OSMS门控技术跟踪运动靶区可以提高靶区的剂量精度,而且对患者不附加任何电离辐射,适合应用于分次间的辅助摆位和分次内的靶区跟踪。

Objective To evaluate the geometric accuracy of target motion measurement and dose accuracy in radiotherapy with optical surface monitoring system(OSMS) to track moving targets. Methods The positions of abdominal phantom were monitored with OSMS and cone beam computed tomography(CBCT), separately. The displacement and rotation of the phantom were achieved by moving treatment couch. Finally, the measurements of phantom position between two methods were compared.Matri XX two-dimensional ionization chamber array mounted on a respiratory motion platform was used to measure the relative dose in phantom under different tracking thresholds. The obtained doses were compared with planned doses, thereby analyzing the gamma passing rates of verification plans with different tracking thresholds. Results The difference between OSMS and CBCT system in measuring the preset displacements of phantom translation and rotation was trivial. When using OSMS gating technology, the smaller the threshold of OSMS was, the higher the gamma pass rate was, and the consistency between relative dose distribution and planned dose was better. Conclusion OSMS which has a high accuracy in monitoring the phantom surface position can be applied to the assistant positioning in radiotherapy. Using OSMS gating technology to track moving targets can improve the dose accuracy of target areas, without adding ionizing radiation to patients. OSMS is suitable for inter-fractional assistant positioning and inter-fractional target tracking.