6 Sigma过程能力控制技术对加速器射野均匀性的评估与改进

Evaluation and improvement of acceleratior’s flatness and symmetry by six sigma capability and control technology

针对医科达Synergy直线加速器均匀性检测过程中出现的不稳定情况,应用6 Sigma过程能力控制技术对采集的直线加速器束流均匀性数据进行统计学分析,评估其稳定性及受控状态。在评估结果不佳的情况下,对X、Y方向上的对称性及平坦度进行相关性分析,建立了合理的多元回归模型,并给出了最优解。改进后,加速器束流均匀性有明显的改善,整体达到了预期的稳定状态。利用单值-移动极差图监控束流均匀性,对不稳定状态及时发出预警,及时、准确地采取适当的措施来校正束流均匀性,进而长时间维持均匀性在平稳状态,实现了加速器的质量控制由被动检测进入主动预防并修正阶段。

[Background]Six sigma capability and control technology has been used to analyze the data of synergistic linear accelerator and evaluate the stability and controlled state.Uniformity of accelerator irradiation field is an important performance parameter of intensity-modulated radiation therapy(IMRT)with linear accelerator.[Purpose]This study aims to employ six sigma capability and control technology in IMRT to keep the beam uniformity stable for a long time.[Methods]X-ray uniformity data were collected and recorded for 9 consecutive months,once a week.A data record includes four types of parameters:X-direction flatness,X-direction symmetry,Ydirection flatness and Y-direction symmetry.First of all,the correlation between symmetry and flatness in the X,Y direction in the irradiation field of X-ray beam were analyzed.At the same time,a reasonable multiple regression model was established to search an optimal solution of beam uniformity.Then,the uniformity of accelerator would be adjusted to the optimal solution.Finally,the Individual and Moving Range Charts(I-MR)were applied to monitor the uniformity,and to provide timely warnings when unstable conditions exist.[Results]Through the above improvements,the uniformity performance is better and stable.The results reflect the instability of beam uniformity.[Conclusion]This technology can change the quality control of the accelerator from the pattern of passive detection mode to the active prevention mode.