What is adaptive radiotherapy?
Adaptive radiotherapy (ART) is an image-guided treatment approach that re-evaluates and updates the radiation plan against the patient's actual anatomy on the day of treatment — rather than treating from a plan made days or weeks earlier.
This page is a plain-language, evidence-based introduction to ART: why static plans fall short, how online and offline adaptive workflows differ, the role of CT and CBCT imaging, and the published outcomes that explain why shorter, more precise courses are now becoming standard of care.
Watch: what adaptive radiotherapy actually does
Adaptive radiotherapy by the numbers
Three peer-reviewed findings that explain why adaptation matters.
of online-adapted fractions change the plan
Multi-site CBCT-guided online ART experience: the daily plan is meaningfully different from the original plan in the large majority of fractions.
fewer significant urinary side effects vs non-adaptive
Randomized phase III data of tightly margined, image-guided adaptive prostate SBRT show substantially lower rates of clinically meaningful acute genitourinary symptom flares — with the largest differences seen in patient-reported endpoints — compared to conventionally guided treatment.
sessions can replace 20–35 conventional treatments
Hypofractionated stereotactic regimens (e.g., 5-fraction prostate SBRT) reach cancer-control outcomes comparable to conventional 20–39 fraction courses.
Numerals refer to the references listed below. Outcomes vary by disease site, technique, and patient factors; figures shown are representative of published trials.
Why a static plan isn't enough
Conventional radiation plans are built once, on a single diagnostic CT, and then delivered unchanged across weeks. The body — and the cancer inside it — does not stay still that long.1,3
Tumors shrink and shift
Between simulation and the final fraction, head & neck and lung tumors commonly lose 20–40% of their volume, while organs like the bladder, rectum, and uterus move centimeters with daily filling.
Margins expose healthy tissue
Because traditional planning can't see day-to-day anatomy, planners add a planning target volume (PTV) margin around the tumor to account for uncertainty — and that margin is healthy tissue receiving full dose.
Setup error compounds over weeks
Conventional courses run 20–35 fractions over 5–9 weeks. Small daily setup errors and anatomic drift accumulate, eroding the precision the original plan promised.
See It in Action
Online vs offline adaptive
There are two flavors of adaptive radiotherapy in clinical use today. They differ in when the replan happens — and that timing changes how much the plan can react to the patient's day-to-day anatomy.2
Offline adaptive
Replan between sessions
After one or more fractions, the team reviews recent imaging, decides the plan no longer fits the patient's anatomy, and redesigns the plan in the planning system. The patient is treated on the new plan at the next visit.
Online adaptive
Replan at the moment of treatment
The patient is imaged on the treatment couch, the plan is recalculated against today's anatomy, the physician approves the adapted plan, and treatment is delivered — all in one visit, before the patient gets up.
The Akesis Gemini360RT we operate at 5D Cancer Services delivers online adaptive treatment — your plan is recalculated against your anatomy at every fraction, before a single beam fires.
The role of imaging
Adaptive radiotherapy is only as good as the picture it's reacting to. Different modalities make different trade-offs between speed, detail, and where in the workflow they live.3
CT simulation
Sets up the original treatment plan
A high-resolution CT scan acquired days before treatment begins. Provides the electron-density information physicists need to compute dose, but represents a single moment in time.
CBCT (cone-beam CT)
What we use at 5D for daily adaptation
A 3D scan acquired in the treatment room with the patient in treatment position, immediately before the beam is delivered. Modern CBCT supports automated contouring and online replanning.
MRI
Best soft-tissue contrast — used by MR-Linac systems
Some adaptive systems integrate MRI directly into the treatment room (an MR-Linac) for the highest soft-tissue contrast. We do not operate an MR-Linac; this is included for educational comparison only.
MRI is included for context only. The Gemini360RT we operate uses onboard CBCT for daily image guidance and adaptation — we do not offer MR-Linac treatment.
How AI makes online adaptation possible
Online adaptation only works when contouring, dose calculation, and plan QA happen fast enough to keep the patient on the table. Modern AI-driven workflows have collapsed those steps from hours to minutes.5
Automated contouring
Deep-learning models propose contours of the tumor and surrounding organs on the daily image in seconds, not the 20–60 minutes a manual recontour would take. Physicians review and approve, but they no longer start from a blank slate every fraction.
On-couch replanning
Rapid dose calculation and plan re-optimization compress a process that historically took hours into minutes — short enough to keep the patient on the treatment table for a single, adapted session.
Quality assurance built in
Independent dose checks and automated plan-quality metrics run in the background, so the adapted plan that reaches the beam has been verified before a single monitor unit is delivered.
What this means for patients
When the plan reflects today's anatomy instead of last month's, the dose actually delivered to the tumor goes up and the dose to surrounding healthy organs goes down. Multiple peer-reviewed analyses show that the majority of adapted fractions change the plan in clinically meaningful ways — confirming that the static plan was, in fact, drifting.5
That precision is what unlocks hypofractionation: replacing 20–35 daily treatments with a much smaller number of larger, highly targeted doses. Phase III trials in prostate cancer have shown that 5-fraction stereotactic courses achieve cancer-control outcomes comparable to conventional fractionation, with similar or lower acute toxicity.7
And when adaptive precision is used to tighten margins further, randomized data show meaningful drops in side effects — for example, the MIRAGE trial reported a roughly half-rate of significant acute genitourinary toxicity with daily-adapted, image-guided prostate SBRT compared to a conventionally guided arm.6
The MIRAGE trial used MR-guided adaptive SBRT. We cite it because it is the strongest published evidence that tighter, image-guided adaptation reduces side effects — not to imply we operate an MR-Linac. Our adaptation at 5D is delivered with onboard CBCT.
References & further reading
All citations link to the original peer-reviewed source. This page is educational and does not constitute medical advice; please consult our team or your physician for personalized care.
- 1.
Heukelom J, Fuller CD. Head and Neck Cancer Adaptive Radiation Therapy (ART): Conceptual Considerations for the Informed Clinician. Semin Radiat Oncol. 2019;29(3):258–273.
doi.org/10.1016/j.semradonc.2019.02.008 - 2.
Green OL, Henke LE, Hugo GD. Practical Clinical Workflows for Online and Offline Adaptive Radiation Therapy. Semin Radiat Oncol. 2019;29(3):219–227.
doi.org/10.1016/j.semradonc.2019.02.004 - 3.
Sonke JJ, Aznar M, Rasch C. Adaptive Radiotherapy for Anatomical Changes. Semin Radiat Oncol. 2019;29(3):245–257.
doi.org/10.1016/j.semradonc.2019.02.007 - 4.
Heijkoop ST, Langerak TR, Quint S, et al. Clinical Implementation of an Online Adaptive Plan-of-the-Day Protocol for Nonrigid Motion Management in Locally Advanced Cervical Cancer IMRT. Int J Radiat Oncol Biol Phys. 2014;90(3):673–679.
doi.org/10.1016/j.ijrobp.2014.06.046 - 5.
Sibolt P, Andersson LM, Calmels L, et al. Clinical implementation of artificial intelligence-driven cone-beam computed tomography-guided online adaptive radiotherapy in the pelvic region. Phys Imaging Radiat Oncol. 2021;17:1–7.
doi.org/10.1016/j.phro.2020.12.004 - 6.
Kishan AU, Ma TM, Lamb JM, et al. Magnetic Resonance Imaging-Guided vs Computed Tomography-Guided Stereotactic Body Radiotherapy for Prostate Cancer: The MIRAGE Randomized Clinical Trial. JAMA Oncol. 2023;9(3):365–373.
doi.org/10.1001/jamaoncol.2022.6558 - 7.
Brand DH, Tree AC, Ostler P, et al. Intensity-modulated fractionated radiotherapy versus stereotactic body radiotherapy for prostate cancer (PACE-B): acute toxicity findings from an international, randomised, open-label, phase 3, non-inferiority trial. Lancet Oncol. 2019;20(11):1531–1543.
doi.org/10.1016/S1470-2045(19)30569-8
Want to see what adaptive looks like for your case?
Our team in St. George reviews diagnostic imaging and pathology to determine whether adaptive radiotherapy is appropriate. Most consultations are scheduled within a week.
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Adaptive radiotherapy by cancer type
Each cancer presents unique anatomy and motion challenges. Explore how the Akesis Gemini 360 addresses them — with clinical evidence, treatment workflows, and comparisons for your specific diagnosis.
