Proton Stereotactic Radiosurgery with Shoot-Through Proton Arc Beams: Planning Feasibility and Dosimetry
W Gu*, J Zou, B Teo, L Dong, S Nagda, M Alonso-Basanta, T Li, University of Pennsylvania, Philadelphia, PA
Presentations
PO-GePV-T-187 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
ePoster Forums
Purpose: The unique physics of proton and the increasing number of proton centers provide potential applications of protons-based stereotactic radiosurgery (SRS). Compared with Intensity-Modulated Proton Therapy, rotating high-energy transmission proton beams has the potential of superior dosimetry, with sharper penumbra and more beams. We intend to investigate the dosimetry feasibility of Transmission beam-based Proton Arc(TPArc) for intracranial SRS.
Methods: Three patients with brain single metastasis were retrospectively tested. matRad(open-source platform in Matlab) was used for proton dose calculation and in-house developed code used for optimization. TPArc plans were generated using one full coplanar arc, and two half arcs at 30° and 330° couch angles, with 5° spacing between control points. At each sub-beam, single energy proton pencil beams (236MeV from matRad generic beamline), were positioned to cover the target. robust-optimized plans (TPArc-RO), optimizing GTV, were generated using worse-case algorithm, under 2mm setup uncertainty, 2.4% range uncertainty, and 1° rotational uncertainty. TPArc plans optimized to PTV (2mm expansion to GTV), with conventional methods (TPArc-Conv) were generated to investigate robustness difference. They were compared against clinical Linac-based SRS plan using VMAT.
Results: The three methods generated plans with similar GTV coverage. Compared with VMAT, both TPArc-Conv and TPArc-RO plans show lower brain doses and improved dose fall-off. But TPArc-Conv plan is affected by uncertainties, with a worst reduction of 8.5% of GTV D99%. TPArc-RO plans maintained good GTV coverage under worst uncertainties cases. On average the Brain V12Gy, V6Gy, and V3Gy was reduced by 4.9cc, 20.2cc and 81.3cc by TPArc-RO from VMAT plans.
Conclusion: This proof-of-concept study demonstrated that transmission beam based proton arc plan provided superior dose fall-off, normal tissue sparing and robustness under various setup and range errors. It showed TPArc is a dosimetrically feasible solution for SRS. In further work, optimal proton energy and delivery efficiency will be investigated.
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