Based on DVH reconstruction system to investigate the reliability of three-dimensions gamma rule
Objective To establish and validate the model of VeriSoft DVH,then based on this mode,reliability of three dimensions gamma rule in evaluating the dose verification results was investigated.Methods DVH model of Octavius 4D 1500 system was build first.Then,modules composed of solid water,EBT3 film,homemade foam and ionization cham-ber(Razor)were established.These modules,together with fixed and rotational fields were used to verify the accuracy of DVH model.After that,twenty lung cancer patients were chosen from First Affiliated Hospital of Zhengzhou University whose treatment plans generated by Monaco were delivered by VersaHD Linac and were performed on Octavius 4D 1500 system respectively.Dose calculated in radiotherapy plan and measured results were compared for these patients.One-tenth of the maximum dose was set as the threshold value,and 3％/3 mm,3％/2 mm,2％/3 mm,2％/2 mm,1％/2mm,2％/1 mm,1％/1 mm were selected to calculate the global and local three dimensions y pass-rate.The DVH differ-ence between Monaco calculate and reconstruction by VeriSoft DVH were also evaluated.Results Dose deviation be-tween reconstructed and Monaco calculated,and dose difference between measured and Monaco calculated were both less than 4.46％,indicating that the DVH model was reliable.Three of the cases with large dose deviations were found using the global gamma with 3％/2 mm.Average value of the mean dose difference to the targets was small.To the OARs,V30 Gy and V40 Gy of the heart and maximum dose of the affected lung have large average deviation up to 9.27％,14.25％and 9.51％.High correlation was only found between the heart mean dose deviation and all y pass rates,and moderate correlation was found between GTV mean dose deviation and all y pass rate.To other dose deviations,no correlation was found between them and correspond y pass rate.Conclusions The DVH model is established accuracy though a reliable process and its reliability is validated.The gamma evaluated based on Octavius 4D is reliable in most cases,but a false negative result would occur by accident.Therefore,it is suggested that three dimensions reconstruction-based evaluation method combined with gamma rule would be a better choice.
dose volume histogram reconstruct modeldosimetry verificationthree gamma evaluationlung cancer
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