Abstract
Purpose:Volumetric modulated arc therapy (VMAT) utilizes dynamic gantry rotation, dynamic MLC and varying dose rate. However, in addition the collimator angle could be changed dynamically, thus, increasing the degrees of freedom for the optimization, which might lead to improved dose distributions. This work investigates the feasibility of including a dynamic collimator rotation for VMAT.Methods:In this work a 20×20×20 cm3 water phantom with a cigar shaped target volume and a spherical shaped critical structure was used. By means of the Eclipse Research Scripting a predefined collimator rotation was included in a not yet optimized treatment plan, consisting of one partial arc, by assigning for each dicom control point a different collimator angle. Thereby the collimator rotation takes into account the physical limitations for the delivery. This treatment plan was then imported into Eclipse using the Eclipse Research Scripting interface and VMAT PRO3 optimization was performed in a research version of Eclipse. For the dose calculation of the optimized treatment plan the Swiss Monte Carlo Plan (SMCP) was used. Similarly, a dose distribution was determined using a static collimator angle as applied in VMAT. The resulting DVHs for the target and the critical structure were compared for the two treatment plans.Results:A VMAT treatment plan with dynamically moving collimator angle was successfully generated. The comparison of the DVHs for the target volume shows a slight improvement of the coverage and dose homogeneity for the treatment plan using dynamic collimator rotation. Additionally, the dose to the critical structure could be reduced when using the moving collimator rotation.Conclusion:The usage of dynamic collimator rotation for VMAT is feasible and has the potential to improve the dose distribution for the target while reducing the dose to critical structures. This work was supported by Varian Medical Systems.This work was supported by Varian Medical Systems.
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