Kong Cw, Yu Sk, Cheung Ky, Geng H, Ho Yw, Lam Ww, Wong Wk
Hong Kong Sanatorium and Hospital, Happy Valley, Hong Kong, China SAR.
Biomed Imaging Interv J. 2012 Apr;8(2):e14. doi: 10.2349/biij.8.2.e14. Epub 2012 Apr 1.
To evaluate the performance of 2D-array I'mRT MatriXX for dose verification of TomoDirect treatment plans.
In this study, a 2D-array ion chamber device - the I'mRT MatriXX and Multicube Phantom from IBA - was used for dose verification of different TomoDirect plans. Pre-treatment megavoltage computed tomography (MVCT) was performed on the phantom setup for position correction. After the irradiation of treatment plans on the I'mRT MatriXX and Multicube Phantom, the measured doses of coronal planes were compared with those from the planning calculations for verification. The results were evaluated by comparing the absolute dose difference in the high dose region as well as the gamma analysis of the 2D-dose distributions on the coronal plane. The comparison was then repeated with the measured dose corrected for angular dependence of the MatriXX.
When angular dependence is taken into account, the passing rate of gamma analysis is over 90% for all measurements using the MatriXX. If there is no angular dependence correction, the passing rate of gamma analysis worsens for treatment plans with dose contribution from the rear. The passing rate can be as low as 53.55% in extreme cases, i.e. where all doses in the treatment plan are delivered from the rear.
It is important to correct the measured dose for angular dependence when verifying TomoDirect treatment plans using the MatriXX. If left uncorrected, a large dose discrepancy may be introduced to the verification results.
评估二维阵列I'mRT MatriXX在容积调强弧形治疗（TomoDirect）治疗计划剂量验证中的性能。
在本研究中，使用二维阵列电离室装置——I'mRT MatriXX和IBA公司的多立方体模体，对不同的TomoDirect计划进行剂量验证。在模体设置上进行治疗前兆伏级计算机断层扫描（MVCT）以进行位置校正。在I'mRT MatriXX和多立方体模体上照射治疗计划后，将冠状面的测量剂量与计划计算剂量进行比较以进行验证。通过比较高剂量区域的绝对剂量差异以及冠状面上二维剂量分布的伽马分析来评估结果。然后对经MatriXX角度依赖性校正后的测量剂量重复进行比较。
考虑角度依赖性时，使用MatriXX进行的所有测量中伽马分析的通过率超过90%。如果不进行角度依赖性校正，对于有后方剂量贡献的治疗计划，伽马分析的通过率会变差。在极端情况下，即治疗计划中的所有剂量都从后方递送时，通过率可低至53.55%。
使用MatriXX验证TomoDirect治疗计划时，对测量剂量进行角度依赖性校正是很重要的。如果不进行校正，可能会给验证结果引入较大的剂量差异。
