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Non-Coplanar Helical Arc Radiation Therapy (NCHART)

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W Lu

M Chen1 , T Zhang2 , S Jiang1 , W Lu1*, (1) UT Southwestern Medical Center, Dallas, TX, (2) Washington University School of Medicine, St. Louis, MO


MO-F-CAMPUS-TT-3 (Monday, July 31, 2017) 4:30 PM - 5:30 PM Room: Therapy ePoster Theater

Purpose: To design a radiotherapy machine that is (1)flexible with a large degree-of-freedom (DOF) in beam directions and in independent beamlets, (2)efficient by allowing the aperture to open as large as necessary, and (3)precise with geometric stability. We propose Non-Coplanar Helical Arc Radiation Therapy (NCHART).

Methods: The NCHART technique can be implemented on either a ring-gantry or C-arm platform. It uses simultaneous gantry rotation and couch translation and dose rate modulation. NCHART has the following features: •A rotating gantry radiation delivery with a translating couch is equivalent to a helical source motion. •The treatment head is equipped with 2D MLC (maximal dimension of 40×40 cm2. •The source (through couch translation) starts at 20cm prior to the superior edge and ends at 20cm after the inferior edge of the tumor. •The non-coplanar beams are realized through the off-axis flattening filter free beam profile •The helical trajectory provides a large treatable range with single pass, i.e. no couch kicks or field junction issues.We also developed a non-voxel-based broad-beam (NVBB) framework with direct leaf optimization to generate high quality plans in NCHART.

Results: Simulations with various complex treatment geometries showed the capability of NCHART that utilized non-coplanar beams, consistently improved target conformity and reduced organ-at-risk dose compared with VMAT and TomoTherapy.

Conclusion: NCHART combines delivery modes of multi-arc VMAT, TomoTherapy, and TopoTherapy. NCHART allows efficient delivery of non-coplanar beams for arbitrary length of tumor with full intensity modulation in a single patient setup, even for TBI and multiple metastases treatments. No beam trajectory, gantry angle or couch optimization is involved. Therefore, simple or full automatic planning is feasible. The method can be applied to any rotational gantry, including ring gantry and c-arm gantry, provided that the c-arm is allowed to rotate back and forth.

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