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BEST IN PHYSICS (THERAPY): Mixed Beam Treatment Technique Using Photon Dynamic Trajectories and Modulated Electron Beams

S Mueller

S Mueller1*, P Manser1 , W Volken1 , D Frei1 , D M Aebersold1 , M F M Stampanoni2 , M K Fix1 , (1) Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Switzerland, (2) Institute for Biomedical Engineering, ETH Zurich and PSI, Villigen, Switzerland


TH-CD-708-6 (Thursday, August 3, 2017) 10:00 AM - 12:00 PM Room: 708

Purpose: To develop a treatment technique for mixed beam radiotherapy (MBRT) exploiting photon dynamic trajectories (DTs) and modulated electron beams shaped with the photon multileaf collimator (pMLC).

Methods: A deliverable gantry-couch track is determined by minimizing the overlap of the OARs with the PTV. An associated dynamic collimator rotation is established with reduced area between the pMLC leaves and the PTV contour obtaining a complete DT. A simulated annealing based direct aperture optimization is performed to simultaneously optimize photon apertures of several beam directions along the DT and electron apertures of manually defined beam directions. Afterwards, the photon apertures are discarded and instead two photon DT arcs are optimized upon the deliverable dose distribution of the optimized electron apertures using a research version of the Varian photon optimizer. This process is applied for a squamous cell carcinoma case with a PTV including a deep-seated part adjacent to the brain and the left eye. The dose distribution of the resulting MBRT plan is compared to those of a two-arc photon DT radiotherapy (DTRT) plan using the same DT as the MBRT plan and a conventional non-coplanar five-arc VMAT plan.

Results: The dose homogeneity in the PTV of the MBRT plan is similar to the DTRT and VMAT plans, while the mean dose to the parallel OARs are 12-53% and 22-55% lower, D2% to the serial OARs are 0-12% and 15-68% lower and the low dose bath expressed as V10% to normal tissue is 15% and 33% lower for the MBRT plan compared to the DTRT and VMAT plans, respectively.

Conclusion: The developed technique for MBRT offers a great dosimetric potential for future treatments of sites like head & neck, breast and squamous cell carcinomas with superficial targets possibly including a deep-seated part.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by Varian Medical Systems.

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