Biology-guided Radiotherapy

This is the authors' abstract. We don't add key points for this paper.

Background: Advancements in technology allowing the advent of stereotactic body radiation therapy (SBRT) and inclusion of PET imaging into radiation oncology workflows have shaped modern radiation oncology treatment planning and delivery. The X1 (RefleXion Medical) is a novel radiation delivery device that is equipped with PET arcs, which guide the linear accelerator (linac) portion of the machine, allowing for the delivery of biology-guided radiotherapy (BgRT) in which the PET signal is actively used to target external beam radiotherapy during treatment delivery. We provide a review of the X1 machine and BgRT workflow, as well as early cases delivered on the X1 device. Patients and Methods: The X1 device and BgRT workflow are described in detail. Key components of the machine include its two 90-degree PET detector arcs, which collect PET data in real time, enabling the delivery of BgRT. The BgRT workflow is unique from the standard radiation oncology workflow in that radiotracer injections and X1 PET scans are performed as a part of treatment planning, as well as immediately before and during each fraction of BgRT for treatment guidance. Results: We describe 4 of the first BgRT cases including successful treatments of lung (peripheral and central) and bone tumors, as well as unsuccessful treatment of a bone metastasis. Conclusions: BgRT is an emerging treatment paradigm in which PET signals are used in real time to direct external beam radiotherapy. Currently cleared for FDG-guidance for lung and bone tumors, further research is needed to expand the indications and availability of various radiotracers for BgRT delivery.