# Biology-guided radiotherapy (RefleXion X1, SCINTIX)

Source: https://onco.cc/technologies/biology-guided-radiotherapy/  
OnCo record `biology-guided-radiotherapy` (Technology). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

A radiotherapy machine with PET detectors built in: the tumour's own radioactive tracer signal tells the beam where to fire, hundreds of times a second, so moving tumours and several metastases can be tracked and treated without external markers.

## Summary

RefleXion's X1 is a ring-gantry linac that also carries PET detector arcs and a fan-beam kilovoltage CT. In SCINTIX mode the patient receives a dose of fluorodeoxyglucose, and as the gantry rotates the machine detects pairs of annihilation photons from the tumour and, within a fraction of a second, fires short beamlets back along the lines they came from. The tumour therefore steers its own treatment, motion is handled without fiducials or breath-hold, and in principle several metastases can be treated in one session with the emissions from each guiding its own dose. The system was authorised in the United States in 2023 for lung and bone tumours, primary or metastatic, that take up FDG, and can also deliver conventional image-guided and stereotactic treatments with CT guidance.

It is one vendor's platform with a small number of installations, treatment requires a tracer injection and tumours with enough uptake, sessions are longer than standard radiotherapy, and the clinical claim that biology guidance improves outcomes in oligometastatic and polymetastatic disease is still being tested. Tracers other than FDG, such as PSMA ligands for prostate cancer, are the obvious next step.

## Fields

- Kind: Technology
- Status: emerging
- Last checked: 2026-09-17
- Tags: machines-wave
- Principle: PET detectors on a rotating ring gantry detect coincident annihilation photons from a tracer in the tumour and trigger linac beamlets back along the detected lines of response with sub-second latency, so emissions from the target steer the dose.
- Since: 2023
- Strengths: Tumour signal tracks motion without fiducials; Aims at treating multiple metastases in one session; Also delivers conventional CT-guided radiotherapy
- Limitations: Needs a tracer injection and adequate uptake; Longer sessions and few installations; Outcome benefit still under study

## Sources

- RefleXion Medical: https://reflexion.com

## Connected records

- technologies: [FDG PET](https://onco.cc/technologies/fdg-pet/), [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/), [MR-guided adaptive radiotherapy](https://onco.cc/technologies/mr-linac/), [PET/CT](https://onco.cc/technologies/pet-ct/), [PSMA PET](https://onco.cc/technologies/psma-pet/), [Ring-gantry linacs (Halcyon, Ethos)](https://onco.cc/technologies/ring-gantry-linac/), [SBRT / SABR (stereotactic radiotherapy)](https://onco.cc/technologies/sbrt/), [Stereotactic ablative radiotherapy for oligometastatic disease](https://onco.cc/technologies/sabr-oligometastases/)
- cancers: [Metastatic cancer (cancer that has spread)](https://onco.cc/cancers/metastatic-cancer/), [Non-small-cell lung cancer](https://onco.cc/cancers/nsclc/), [Osteosarcoma](https://onco.cc/cancers/osteosarcoma/), [Prostate cancer](https://onco.cc/cancers/prostate/)
- fronts: [Devices & Physical Therapies](https://onco.cc/fronts/devices/), [Imaging](https://onco.cc/fronts/imaging/), [Radiation Therapy](https://onco.cc/fronts/radiation/)
- companies: [RefleXion Medical](https://onco.cc/companies/reflexion/)
- institutions: [City of Hope](https://onco.cc/institutions/city-of-hope/), [Stanford Health Care / Stanford Cancer Institute](https://onco.cc/institutions/stanford/)

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