Comparison of validation results and leaf open time before and after upgrading of helix tomotherapy planning system / 中华放射肿瘤学杂志

ABSTRACT

Objective:To compare the leaf open time (LOT) parameters and γ passing rates between the 4.0.4 and 4.2.3 helix Tomotherapy planning systems and evaluate the improvement.Methods:Retrospective comparison of the treatment plans of 345 cases selected by 4.0.4 and 4.2.3 versions was performed. The Machine Specific Sinogram of each plan was extracted from the archived plan file to calculate the LOT. The evaluated LOT parameters included the projection time, the maximum LOT, the mean non-zeros time, the time difference between the projection time and the maximum LOT, the relative count of leaves with LOT greater than maximum LOT minus 5 ms, the relative count of leaves with LOT lower than 100 ms and the beam on time. The γ passing rate (criteria 3 mm/3%, 10% threshold and global error) and the LOT parameters between two version systems were evaluated with the independent t-test. The relationship between the LOT parameters and γ passing rate was analyzed by the multiple linear regression method. Results:The γ passing rate of the Ver 4.0.4 system was 97.86%, significantly lower than 98.6% of the Ver 4.2.3 system ( P<0.001). The time gap between the projection time and the maximum LOT of the Ver 4.2.3 system was significantly less than that of the Ver 4.0.4 system (1 ms vs. 11 ms, P<0.001). For the Ver 4.0.4 system, the multiple linear regression method showed that the maximum LOT ratio and the beam on time were negatively correlated with the γ passing rate (both P<0.001). However, for the Ver 4.2.3 system, only the beam on time showed a negative correlation with the γ passing rate ( P<0.001). Conclusion:The γ passing rate of the Ver 4.2.3 system is significantly higher than that of the Ver 4.0.4 system. The decrease of γ passing rate caused by the leaves near the maximum LOT is properly resolved in the new version system.