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BEST IN PHYSICS (THERAPY): A Highly Efficient Linac Design Optimized for 4pi Radiotherapy

T Zhang

T Zhang1*, W Lu2 , R Khan3 , S Mutic4 , (1) Washington University School of Medicine, St. Louis, MO, (2) UT Southwestern Medical Center, Dallas, TX, (3) Washington University School of Medicine, St Louis, MO, (4) Washington University in St Louis, St Louis, MO


TH-CD-708-1 (Thursday, August 3, 2017) 10:00 AM - 12:00 PM Room: 708

Purpose: Traditional C-arm linear accelerators deliver non-coplanar beams by rotating treatment couch, which imposes the risks of collision, treatment reproducibility and prolongs treatment time. The purpose of this study is to design a novel Linac that can efficiently deliver non-coplanar (4π) plans.

Methods: A compact C-band or X-band Linac is mounted on a ring gantry with a pivoting structure that can rotate the beam in and out of the treatment plane and form a non-coplanar (gimbal) angle. The linac design includes a cone collimator can be used for stereotactic radiosurgery (SRS) treatments, while the multi-leaf collimator (MLC) is used for treating large targets. During radiation treatment delivery, the patient translates longitudinally while the gantry rotates about the central axis. In the meantime, the treatment beam tracks the isocenter by gimballing the Linac head.

Results: The new design can deliver non-coplanar beams either continuously in helical mode or intermittently at discrete couch positions and gantry angles. It can provide sufficient degree of non-coplanar angles for the major treatment sites. Treatment plan quality can be significantly improved with the use of a large number of non-coplanar beams. Besides an efficient and collision-free 4 delivery, the gimbal angle can also be used for rotational setup correction, which eliminates the necessity of a complex robotic couch. The gimbal angle further can be used to increase longitudinal coverage and reduce the length of MLC leaves, thereby simplifying the treatment head. The gimbal motion can further be synchronized with respiratory motion for target tracking.

Conclusion: The novel Linac design with additional gimbal rotation is highly efficient in the delivery of non-coplanar beams without a significant increase of the overall complexity. The gimbal rotation can also be used for target tracking, rotation setup correction and extended field coverage.

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