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Program Information

Dynamic Couch Motion for Improvement of Radiation Therapy Trajectories in DCA and VMAT

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L MacDonald

L MacDonald1*, Dalhousie University, Halifax, Nova Scotia; Dr. Christopher Thomas2 , PhD, MCCPM, Capital District Health Authority, Halifax, Nova Scotia

Presentations

TH-C-12A-5 Thursday 10:15AM - 12:15PM Room: 12A

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 large-scale 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.


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