A Phantom Investigation of the Robustness and Adaptability of a Novel PET LINAC During Lung Cancer Biology-Guided Radiotherapy (BgRT) Characterized by Unplanned Perturbations in the Tumor Trajectory

This novel biology-guided radiotherapy system (BgRT), the RefleXion X1 SCINTIX™ system, uses annihilation photons produced from a PET-avid tumor to plan and then subsequently guide the delivery of beamlets of radiation to the tumor, tracking the dose delivered in real time. The current BgRT system is cleared by the U.S. Food and Drug Administration (FDA) to treat tumors in the lung or bone characterized by periodic or non-periodic motion, respectively. In this work, we assessed the robustness and adaptability of the dose tracking capability under tumor motion perturbation. We designed a phantom study based on a lung case planned under periodic tracking for four-pass (4-Pass) BgRT and then introduced transient translational shifts to the phantom motion continuously under treatment. By comparing the dose delivered under a normal periodic sinusoidal tumor motion to the dose delivered under a perturbed sinusoidal delivery, with a simple perturbation situation characterized by a perturbation introduced at the end of the second pass of the 4-Pass delivery and a more complex situation with perturbation introduced at each of the four passes of the 4-Pass delivery, we assessed the robustness and adaptability of the RefleXion X1 SCINTIX™ system in delivering the correct dose under such circumstances.