In vivo three-dimensional dose validation for intensity-modulated radiotherapy of cervical cancer and the optimal gamma passing rate threshold
Objective To analyze thein vivo three-dimensional dose verification using electronic portal imaging device(EIVD)for intensity-modulated radiotherapy(IMRT)of cervical cancer for investigating the differences between the measured and planned doses,and explore the optimal threshold for gamma passing rate in EIVD quality control based on dosimetric sensitivity.Methods A retrospective analysis was conducted on a cohort of 45 patients with cervical cancer who underwent IMRT at Women's Hospital,School of Medicine,Zhejiang University.During the treatment,all patients underwent EIVD to obtain the measured doses.The passing rate was analyzed using global gamma criteria of 2 mm/2%,2 mm/3%,and 3 mm/3%.Additionally,dose-volume histogram parameters were utilized to evaluate any differences between the measured and planned doses.Pearson correlation analysis was employed to investigate the relationship between the gamma passing rate and dosimetric differences.Furthermore,receiver operating characteristic(ROC)curve was generated to determine the optimal threshold for the gamma passing rate.Results The average gamma passing rates for the criteria of 2 mm/2%,2 mm/3%,and 3 mm/3%were 83.07%±5.25%,91.69%±3.52%,and 95.02%±2.46%,respectively.The Dmean deviation between EIVD measurement and planned dose in the planning target area was 2.43%(P=0.016),while the Dmean deviations in the bladder,rectum,and small intestine were 0.35%,0.46%,and 0.30%,respectively(P>0.05).Pearson analysis revealed a strong correlation between the 3 gamma indexes and dosimetric differences in the PTV(r>0.7),but a weak correlation with organs-at-risk(r<0.7).ROC analysis indicated that the optimal gamma passing rate thresholds for the criteria of 2 mm/2%,2 mm/3%,and 3 mm/3%were 79.06%,90.04%,and 94.19%,respectively.Conclusion The implementation of EIVD can ensure the accuracy of dose delivery within the PTV during IMRT for cervical cancer.Moreover,establishing a gamma passing rate threshold provides a valuable clinical basis for subsequent adaptive IMRT for cervical cancer.
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