Program Information
Individual Volume Based 3D Gamma Indices for Pretreatment VMAT QA
X Jin*, J Yi , C Xie , the 1st Affiliated Hospital of Wenzhou Medical University, Wenzhou, Zhejiang
Presentations
SU-F-P-63 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:
To investigate the feasibility of individual volume based 3D gamma indices for pretreatment volumetric modulated arc therapy (VMAT) QA.
Methods:
Both model- and measurement-based VMAT QA for one- and two-arc VMAT plans were performed with COMPASS system. Percentage dosimetric errors (%DE) of dose-volume histogram (DVH) metrics between TPS and QA reconstructed dose distribution, percentage gamma passing rate (%GP) for individual volume and global gamma indices, as well as the statistical correlations between %GP and %DE were investigated. The sensitivities of different %GP were also investigated.
Results:
The %DE of model-based QA for most DVH metrics of VMAT plans were within 3%. There were 9, 12, and 9 out of 15 metrics %DE, and only 2 out of 15 %DE metrics were correlated with individual volume %GP and global %GP of nasopharyngeal cancer (NPC) with 2%/2 mm, 3%/3 mm and 4%/4 mm criteria, respectively. For prostate cancer, there were 18, 16 and 13 out of 23 %DE metrics, and 19, 12 and 1 out 23 of %DE metrics were correlated with individual volume %GP and global %GP with 2%/2mm, 3%/3mm and 4%/4mm criteria, respectively. The area under curves (AUC) of individual volume %GP were higher than those of global %GP for NPC patients, but with a mixed results for prostate cancer patients.
Conclusion:
Individual volume based %GP were strongly correlated with DVH metrics %DE compared with global %GP for both one- and two-arc VMAT plans. Sensitivity analysis indicated that individual volume gamma indices were feasible for VMAT QA.
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