The application and correlation study of γ rule and DVH evaluation for VMAT dose verification evaluation of cervical cancer patients
Ma YangGuang1, Mai Rizhen2, Pei Yuntong1, Wang Fangna1, Liu Lele1, Guo Yuexin1
1Department of Radiation Oncology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China; 2Department of Medical Equipment, The First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China
Abstract：Objective To evaluate the volumetric modulated arc therapy (VMAT) dose verification of cervical cancer based on γ rule and dose volume histogram (DVH) and to perform correlation analysis between the evaluation results and the dose differences. Methods Twenty cervical cancer VMAT plans were selected and performed on TrueBeam Linac. The delivered point and surface dose was measured by FC-65G and ArcCheck and the results were compared to those calculated by Eclipse. The dose of patients was reconstructed by 3DVH. Then, differences between the reconstructed and plan value of Dmean,D95%,D98% and D2% of PTV, V20Gy of left and right femoral head, V40Gy of rectum, D1cm3 of cord, D98%,D2% and D50% of the 50% prescription iso-dose volume (IDV), were evaluated and 3-dimensional (3D) γ was assessed for each organ. Lastly, Pearson’s correlation coefficient was used to analyze the relationship between point dose difference, 2D γ pass-rate (γ%), γmean and 3D γ% of each organ and the dose difference. Results Small differences were found between the point dose measured, reconstructed and the plan value. Differences between Dmean of PTV, all dose parameters of IDV and plan values were all within 3% and V40Gy of rectum showed the largest difference. As for the 3D γ%, the maximum pass rate was found for the left and right femoral head and the maximum variance for cord D1cm3. There was a moderate correlation between measured and reconstructed point dose deviation and dose difference of each organ, while no significant correlation was found for 2D γ%. Strong correlation was found between 3D γ% of target and D50% of PTV/IDV and no correlation was found for other organs. Conclusion The performance of both γ-and DVH-based evaluation can reveal dose error for dose verification, but both of them have some limitations and should be combined in clinical practice.
Ma YangGuang,Mai Rizhen,Pei Yuntong et al. The application and correlation study of γ rule and DVH evaluation for VMAT dose verification evaluation of cervical cancer patients[J]. Chinese Journal of Radiation Oncology, 2022, 31(5): 450-455.
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2022, Vol. 31 
