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Impact of Detector Array On Per-Beam Planar IMRT QA Gamma Pass Rates

H Cheng*, J Wen , L Hao , X Wang , Xingtai People's Hospital, Xingtai, Hebei


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: To evaluate the effects of specific detector array on the global gamma pass rates and determine the statistical correlation of per-beam IMRT pass rates between predict condition with high evaluated dose resolution and practical condition, whose evaluated dose array was the same as the practical detector.

Methods: A specialized program was designed to selectively sample the planar dose distribution calculated by Eclipse planning system. The sampled dose array was the same as the measurement array of Mapcheck, which is commonly used in plans verification process. The induced-error beams/plans were used as ‘simulated measurements’ to compare with the corresponding data calculated by the error-free plans. The analysis of various gamma criteria, including 1%/1mm, 2%/2mm and 3%/3mm, was performed to evaluate the effects of different detector array. The correlation between actual gamma pass rates and the predicted pass rates was analyzed.

Results: The actual pass rates were different from predicted gamma pass rates with 1%/1mm, 2%/2mm, 3%/3mm criteria; and the difference is more significant with 1%/1mm gamma criteria. According to the results of nonparametric test, the differences between actual pass rates and predicted pass rates was statistically significant. These indicate that the detector array have a great impact on the calculation of gamma index. Moreover, there exists a strong correlation between actual gamma pass rates and predicted gamma rates. The spearman’s correlation was 0.968 at 1%/1mm, 0.96 at 2%/2mm, and 0.93 at 3%/3mm. Actual gamma pass rates is higher than predicted pass rates.

Conclusion: The configuration of detector array has a significant impact on the gamma pass rates. There is a strong correlation between actual gamma pass rates and predicted gamma pass rates. Since actual gamma pass rates is over-evaluated, it is necessary to improve the acceptance gamma pass rates criteria according to the specific array of detectors.


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