# Proton arc therapy

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

## TL;DR

Rotating the proton beam continuously around the patient instead of firing from a few fixed angles, to spread the entrance dose and sharpen the target dose.

## Summary

Proton arc spreads low-weight spots across a continuously rotating gantry, so each direction contributes only part of the dose, improving conformality and robustness to range uncertainty. Vendors have released treatment-planning implementations and first patients have been reported at a small number of centres; a September 2026 search of ClinicalTrials.gov found no randomised comparison against intensity-modulated proton therapy. Delivery time and quality assurance are the practical barriers.

## Fields

- Kind: Technology
- Status: phase-1
- Last checked: 2026-09-08
- Tags: frontier
- Principle: Spot-scanned protons are delivered during continuous gantry rotation, with energy layers distributed across angles so each direction contributes only part of the dose.
- Strengths: Better normal-tissue sparing than fixed-field proton therapy in planning studies; More robust to setup and range error; Runs on existing proton hardware
- Limitations: No comparative clinical outcome data; Long delivery and QA times; Adds planning complexity for uncertain benefit

## Sources

- ClinicalTrials.gov: proton arc therapy: https://clinicaltrials.gov/search?term=proton%20arc%20therapy

## Connected records

- fronts: [Radiation Therapy](https://onco.cc/fronts/radiation/)
- technologies: [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/), [Pencil-beam scanning and intensity-modulated proton therapy](https://onco.cc/technologies/intensity-modulated-proton-therapy/), [Proton therapy](https://onco.cc/technologies/proton-therapy/), [Proton therapy machines: cyclotrons, synchrotrons and single-room systems](https://onco.cc/technologies/proton-therapy-systems/), [SBRT / SABR (stereotactic radiotherapy)](https://onco.cc/technologies/sbrt/)
- companies: [IBA (Ion Beam Applications)](https://onco.cc/companies/iba/), [Mevion Medical Systems](https://onco.cc/companies/mevion/), [Varian (Siemens Healthineers)](https://onco.cc/companies/varian/)
- roadmaps: [Radical oncology: what could change the war by 2035](https://onco.cc/roadmaps/frontier-2035/), [Radiotherapy roadmap: X-rays → shaped beams → fewer fractions, particles and FLASH](https://onco.cc/roadmaps/radiation-roadmap/)
- terms: [Bragg peak](https://onco.cc/terms/bragg-peak/)

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