TH‐C‐12A‐05: Dynamic Couch Motion for Improvement of Radiation Therapy Trajectories in DCA and VMAT

Abstract

Purpose:To investigate the potential improvement in dosimetric external beam radiation therapy plan quality using an optimized dynamic gantry and couch motion trajectory which minimizes exposure to the organs at risk.Methods:Patient‐specific anatomical information of head‐and‐neck and cranial cancer patients was used to quantify the geometric overlap between target volumes and organs‐at‐risk (OARs) based on their two‐dimensional projection from source to a plane at isocentre as a function of gantry and couch angle. QUANTEC dose constraints were then used as weighting factors for the OARs to generate a map of couch‐gantry coordinate space indicating degree of overlap at each point in space. A couch‐gantry collision space was generated by direct measurement on a Varian Truebeam linac using an anthropomorphic solid‐water phantom. A dynamic, fully customizable algorithm was written to generate a navigable ideal trajectory for the patient specific couch‐gantry space. The advanced algorithm includes weighting factors which can be used to balance the implementation of absolute minimum values of overlap, with the clinical practicality of largescale couch motion and delivery time. Optimized trajectories were calculated for cranial DCA treatments and for head‐and‐neck VMAT treatments and compared to conventional DCA and VMAT treatment trajectories.Results:Comparison of optimized treatment trajectories with conventional treatment trajectories indicates a decrease in dose to the organs‐at‐risk between 4.64% and 6.82% (2.39 and 3.52 Gy) of the prescription dose per patient per organ at risk.Conclusion:Using simultaneous couch and gantry motion during radiation therapy to minimize the geometrical overlap in the beams‐eye‐view target volumes and the organs‐at‐risk can have an appreciable dose reduction to organs‐at‐risk.