Technical Analysis Of Volumetric Modulated Arc Therapy

As a new technology, Volumetric modulated arc therapy (VMAT) could achievefast and accurate radiation therapy by changing dynamic factors in360o beamdirections, so more and more institutions in china import this technology. But there aremany parameters involved in the VMAT plan designing. Except the target and organs atrisk need to be given biological objective function for the VMAT plan, arc (o), gantry,energy (MV), increment (o), dose Grid spacing (cm), the Monte Carlo variance (%),smooth, Min MU/Segment and the minimum dose rate must be defined. If theseparameters are not set properly, the optimization time will greatly extend, even theoptimizer is fail. All these will affect the efficiency of clinical works.The purpose of this study is to analyze the impact of the various parameters of theVMAT plan optimization results one by one. The VMAT plans were into seven groupsaccording the seven variables parameters. Only the parameter studied was changed,other parameters and biological objective function were the same in each group. Weanalyze the impact on the assessment results of target and organs at risk, the time ofplan optimization and calculation, the time of plan delivery and the MU for a singleclinical prescription. The values of seven Parameter in research are as follows: energy(MV) were4,8and15; Increment (o) were10o,20o,30o and40o; dose Grid spacing(cm)&the Monte Carlo variance (%) were0.4&3and0.5&4; smooth values were2,5and8; Min MU/Segment were2,5,10,15and20; and the minimum dose valueswere2,5and8MU/Second.Results: the arc and gantry mainly affect the dose distribution and the values ofthem are given according to the target location. Except the Min MU/Segment, doseassessment of the remaining six parameters to the target and organs at risk are notsignificant (P>0.05); The impact of all parameters in the VMAT plans is mainlyreflected in the time of plan optimization and calculation, the time of plan delivery andthe MU for a single clinical prescription. The effect on the time of plan optimizationand calculation is particularly significant. Under the premise of ensuring the clinicaldose, reduce the computation time and improve work efficiency, we analyze theparameters one by one, then get the recommended values of each parameter as follows:energy (MV) is8MV, smooth is5, Min MU/Segment and the Minimum Dose rate areboth5,too. The recommended values of Increment and dose Grid spacing&the Monte Carlo variance are depend on the target size and shape, the recommended valuesof the big target with complex shape are20o and0.5cm&4%and for the small andsample shape target the values are30o and0.4cm&3%.