Effect Of Respiration On The Dosimetry Of Sliding-Window In IMRT

Background and PurposeCurrently,dynamic modulated radiation therapy(IMRT)is widely used in radiotherapy,and is increasingly applied in the treatment for thoracic and abdominal tumors.With the ever-growing clinical requirements for dose distribution,the subfields of dynamic IMRT are getting smaller and smaller.and the dosimetric differences caused by physiological movements,such as respiration,are becoming significant.At present,researches on dosimetry differences as a result of respiratory movement are mainly focuses on difference comparison of dose distribution for a single treatment or the whole course with or without respiratory movement.Specific subfield parameters have not been researched.This study focuses on two important characteristics of dynamic IMRT field for the first time the width of subfield(field width)and the speed of MLC leaf moving(leaf speed)are used to design and research the effects of respiratory on dynamic IMRT field dosimetry.Moreover,whether dynamic intensity modulated technology can be applied in the radiotherapy of breast cancer will be analyzed.Materials and MethodsQuasar drive platform was used to drive the IMRT verification phantom to simulate respiratory movement.A set of sliding window field with different field width and leaf speed was designed to radiate IMRT phantom.Placing EBT2 film in the IMRT phantom to collect the dose distribution during a breathing cycle with or without respiratory motion.Analyzing the film by processing the film and generating a curve analysis film of dose distribution.Comparing the factors such as movement mode,leaf speed and field width,and analyze the reasons.A set of patients' dynamic IMRT field was used to radiate the IMRT phantom,and the dose distributions at the center field were collected with or without respiratory motion in the case of continuous breathing,then comparing and analyzing the reasons by processing the film and generating a dose distribution curve.ResultsIn the single breathing mode,different modes have significantly different effects on the dose distribution;as the leaf speed increases,the amplitude of the dose fluctuation in the field increases significantly;as the width of the field increases,the amplitude of the dose fluctuation is reduced.Small field width and high leaf speed have the most significant effect on the dose distribution.The maximum dose in mode A is not statistically significant,but the minimum dose is 49.93%±13.49%;in mode B,the maximum dose is 204.79%±49.35%,and the minimum dose is 27.53%± 6.96%.However,in the actual radiation field,the dose fluctuation range is significantly reduced in the irradiation field with similar dose distribution curve,and the dose difference is mainly represented by the dose shift.ConclusionWith respiratory motion,its effect on the dose distribution of SW field should be reduced by increasing the radiation field width and/or reducing the leaf speed.