# Adaptive radiotherapy (online replanning)

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

## TL;DR

Re-shaping the treatment plan to the anatomy of the day, using the images taken on the treatment couch, so the dose follows a shrinking tumour or a moving bladder.

## Summary

Conventional radiotherapy delivers a plan drawn on one planning scan for the whole course, even though tumours shrink, weight changes and organs move. Adaptive radiotherapy re-contours and re-optimises the plan, either between sessions (offline) or on the couch in minutes (online) using cone-beam CT or MRI with AI-driven contouring. The MR-linac and CT-based systems such as Ethos made daily online adaptation practical from around 2019, and trials in bladder, cervix, head and neck and lung cancer are testing whether the tighter margins reduce side effects.

## Fields

- Kind: Technology
- Status: emerging
- Last checked: 2026-09-16
- Tags: radiation-wave1
- Principle: Daily imaging, automated re-contouring and rapid re-optimisation produce a new plan matched to that day's anatomy before the beam is delivered.
- Since: 2010
- Strengths: Smaller safety margins; Follows tumour shrinkage; Fewer doses to moving organs
- Limitations: Adds time to each session; Depends on fast, reliable auto-contouring; Benefit still being measured in trials

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Adaptive_radiation_therapy

## Connected records

- fronts: [Radiation Therapy](https://onco.cc/fronts/radiation/)
- technologies: [AI auto-contouring and adaptive planning](https://onco.cc/technologies/auto-contouring-ai/), [Dose painting and biologically guided radiotherapy](https://onco.cc/technologies/dose-painting/), [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/), [Knowledge-based and automated treatment planning](https://onco.cc/technologies/knowledge-based-planning/), [MR-guided adaptive radiotherapy](https://onco.cc/technologies/mr-linac/)
- terms: [GTV, CTV and PTV (target volumes)](https://onco.cc/terms/planning-target-volume/), [Organs at risk and dose constraints](https://onco.cc/terms/organs-at-risk/)

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