RefleXion: Biology Guided Radiotherapy (BGRT)

The Stanford Medicine Department of Radiation Oncology is the first radiation oncology program in the world to test a new biology-guided radiation therapy platform known as RefleXion X1.

The RefleXion X1 machine received marketing clearance from the U. S. Food & Drug Administration (FDA) for stereotactic body radiotherapy (SBRT), stereotactic radiosurgery (SRS) and intensity modulated radiotherapy (IMRT). The RefleXion X1 machine combines a 6MV linear accelerator, 16-slice onboard fan-beam CT, on board PET detector and a rotating ring gantry.

RefleXion X1 is the first device to combine radiotherapy with PET technology. When PET radiotracers are introduced into the body, cancer absorbs them and acts like a biological beacon. The biology-guided radiotherapy (BgRT) technology will synchronize these data with the linear accelerator to direct radiotherapy to tumors with sub-second latency. This has the potential to increase the therapeutic ratio of high dose ablative radiotherapy delivered to primary or metastatic tumors.  

Stanford Medicine will conduct a phase 1 clinical trial that begins to evaluate the performance and safety of BgRT.  BgRT is not currently available for routine clinical use.

BGRT Technology

BGRT uses PET signal as a biologic fiducial to track tumors and deliver radiotherapy.  The RefleXion X1 machine continuously acquires limited time sampled (LTS) PET images to deliver a partial fluence of radiation. (Figure 1) Over a treatment session the delivered partial fluences add up to the intended radiation fraction dose.  For mobile tumors, BGRT can reduce the need to treat the target with a large margin to account for intrafraction motion. (Figure 2)

Figure 1. BgRT principle of linear superposition. Just as the LTS images, Xt, sum to the full PET image X, the derived partial fluences sum to the complete intended fluence.

Figure 2

Images courtesy of RefleXion Medical, Inc. © 2021. These images have previously appeared in the British Journal of Radiology and Clinical and Translational Radiation Oncology.

Ongoing Areas of Research Related to BGRT

  • Prospective Phase I trial to identify performance and safety of BGRT
  • Dosimetric quality assurance for BGRT
  • Novel imaging projects using the X1 system
  • Treatment planning techniques with BGRT
  • Population based studies to evaluate epidemiology, patterns of care and outcomes for patients with metastatic disease

Clinical Trial

Performance and Safety of Biology-Guided Radiotherapy using the RefleXion Medical Radiotherapy System (BIOGUIDE-X)


Cohort I: To identify the recommended FDG dose that enables BgRT on the RefleXion X1 system

Cohort II: To determine the performance and safety of an emulated BgRT plan 

Stanford Medicine is currently accepting patients for this trial.

Lead Sponsor: Stanford Medicine


Device: RefleXion X1

Phase: I

Refer a Patient: Phone: 650-498-6000