Hybrid Forward and Inverse Planning Approach For Lattice Radiation Therapy
Presentations
PO-GePV-T-261 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
ePoster Forums
Purpose: To demonstrate a hybrid forward and inverse planning approach for spatially fractionated Lattice Radiation Therapy (LRT).
Methods: Patients were planned in Eclipse to deliver 18 Gy to 0.5 cc vertices while maintaining 2 Gy dose to periphery of the tumor. Approximately 1% of GTV was covered by vertices with peak to valley fall difference of at least 8 Gy. All the clinically treated plans utilized a hybrid approach of arc fields focused simultaneously on multiple vertices to deliver ~15 Gy with inverse planned supplementary fields to deliver the remaining homogenous dose to the full GTV. The vertex focused fields simultaneously treat multiple vertices along the MLC axis with regularly placed apertures. Three optimization approaches were considered based on the geometry of the GTV-1) Hybrid combination of forward planned conformal arcs with static MLCs to deliver most of the vertex dose, with inverse planned VMAT/IMRT fields to deliver the remaining peripheral dose.2) Hybrid combination with dynamic MLCs conforming to the vertices.3) Fully inverse planned VMAT fields to deliver the entire vertex as well as peripheral dose.
Results: 1) The static MLC approach produces the sharpest dose gradients in peak-to-valley dose but is limited to target volumes where all the vertices can be placed along straight axis.2) The dynamic MLC approach produces a good compromise of high dose gradients for the vertices while allowing the flexibility to cover vertices away from the optimal axis.3) VMAT approach is the most straightforward but requires manual placement of vertices and achieves the lowest peak-to-valley fall off due to the dose spillage.
Conclusion: There are multiple feasible approaches for linac-based LRT. A hybrid approach of combining forward-planning with inverse optimization can be used to significantly reduce treatment time and produce sharp dose gradients to achieve the necessary peak-to-valley dose fall-off.
Keywords
Treatment Planning, Stereotactic Radiosurgery, Conformal Radiotherapy
Taxonomy
TH- External Beam- Photons: Development (new technology and techniques)
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