Study On The Effect Of Respiratory Movement On Dose Distribution Of Lung SBRT

In recent years,stereotactic body radiation therapy（SBRT）has gradually developed and matured,and has been widely in the treatment of lung cancer.It is characterized by a small fractions and a large dose of one fractions compared with conventional radiotherapy,so it requires higher mechanical accuracy of accelerator and radiotherapy accuracy.This paper mainly focuses on the following aspects of SBRT in lung cancer.（1）Feasibility research of RIT113 software for verifying the accuracy of accelerator isocenter.The repeatability and accuracy of RIT113 isocenter verification were tested by introducing known displacements and repeated measurements based on the Winston-Lutz experiment.The experimental results show that the software can measure the introduced displacement well,and has good repeatability.The software can be used to measure accelerators isocenter.This paper provides a method for clinical validation accelerators isocenter,and ensuring the accuracy of subsequent experiments.（2）Effect of respiratory movement on target size and dose distribution in lung cancer.End-to-end experiments were performed using Quasar respiratory phantom.This paper studies six respiratory curves with different respiratory amplitude and cycle.Comparing target size delineation based on 3D-CT and 4D-CT,it was found that target delineation based on 3D-CT significantly underestimated the actual tumor size.The target delineation based on 0%-90% respiratory phase was the closest to the actual tumor size.The target delineation method based on maximum density projection（MIP）and average density projection（AIP）both underestimates the target range,but the method based on MIP is closer to the actual tumor size.Therefore,the target delineation method based on MIP can be used in clinical practice to reduce the workload.Three plans with different energy patterns and dose rates were developed for the target area delineation in 0%-90%respiratory phase.The dose distributions were measured with respiratory movement（dynamic measurement）and without respiratory movement（static measurement）,and the measured results were compared with the planned dose distribution.Static measurement results are in good consistency with the planned dose distribution.The dynamic measurement results are as follows: different respiratory cycle,energy patterns and dose rate in the center of the coronal axial profile,the width of 100% prescription dose and gamma pass rate were no significant difference.The greater the respiration,the lower the gamma pass rate,and in the superior-inferior（SI）direction there was an obvious missing doses.（3）Effect of respiratory gating on target size and dose distribution in lung cancer.Based on experiment（2）,respiratory gating experiment was carried out.30%-60%respiratory phases were selected for respiratory gating therapy.The experimental results showed that the size of target is significantly smaller than that of target delineation based on 0%-90% respiratory phase.Three plans were also made for each target area,and the plans were delivered with（gating measurement）and without（static measurement）respiratory movement.For the respiratory movement with amplitude of 1cm,the results of static measurement and gated measurement were similar,and there was no statistical difference in the gamma passing rate.For the respiratory movement with amplitude of2 cm,the dose loss at the edge of the target can be seen even with the use of respiratory gating technique in the SI direction.Compared with experiment（2）which without the use of respiratory gating,the dose distribution in the target area was improved by respiratory gating.In stereotactic body radiation therapy of lung cancer,respiratory movement is the main reason affecting the accuracy of dose distribution in target area,and corresponding respiratory control methods should be adopted for target area with large respiratory range.