MR-LINAC: MRI-GUIDED
ADAPTIVE RADIATION THERAPY

MR-LINAC integrates a magnetic resonance imaging (MRI) scanner with a linear accelerator (LINAC) in a single system, allowing radiation to be planned and delivered using real-time high-quality soft tissue imaging. It solves the fundamental problem of uncertainty in conventional radiation therapy — the fact that a tumour's exact position during treatment often differs from its position during planning.

“Conventional radiation treats where the tumour was. MR-LINAC treats where the tumour is — right now, in real time.”

• Elekta Unity (1.5 Tesla)

  1.5T MRI providing high-resolution anatomical images; 7 MV flattening-filter-free LINAC; ring gantry design; online adaptive workflow using MR-Linac Consortium protocols. Widely installed at major cancer centres globally.

• ViewRay MRIdian (0.35 Tesla)

  0.35T MRI with lower field strength but effective soft tissue guidance; 6 MV LINAC; C-arm gantry; integrated real-time beam gating driven directly by the MRI signal. Particularly used for upper abdominal and thoracic tumours where respiratory gating is critical.

• Why MRI Guidance Changes Everything

  CT (used in conventional radiation) shows bone and air well but provides poor soft tissue contrast for tumours in the pancreas, prostate, rectum, and cervix. MRI provides superior soft tissue contrast — making tumours clearly delineable — and can image continuously during treatment delivery.

• Online Adaptive Radiation Therapy (ART)

  MR-LINAC enables daily re-planning based on that day's MRI — accounting for tumour shrinkage, organ filling, and positional change. The plan is always optimised for the patient's actual anatomy at the moment of treatment, not from an earlier scan.

Each MR-LINAC session follows a structured adaptive workflow that takes 45–90 minutes. The additional time compared to conventional radiation is what delivers the clinical benefit.

1. 1

   Daily MRI Acquisition at Treatment Position

   A high-quality MRI is acquired with the patient positioned on the treatment couch. This shows current tumour and organ anatomy, including any changes since the last session.

2. 2

   Contouring Review and Adaptation Decision

   The radiation oncologist compares the day's MRI to the original plan. If the bowel has moved closer, or the tumour has shrunk, the plan is adapted accordingly.

3. 3

   Online Re-Planning: Adapt-to-Position or Adapt-to-Shape

   Adapt-to-position shifts the plan to match the current tumour location. Adapt-to-shape goes further — re-contouring the tumour on today's MRI and generating a fully new optimised plan from scratch.

4. 4

   Physics Quality Assurance and Plan Approval

   The adapted plan undergoes rapid QA verification by the medical physics team. The radiation oncologist provides final clinical approval before any radiation is delivered.

5. 5

   Real-Time MRI-Guided Beam Delivery

   MRI images are acquired continuously during radiation delivery. On MRIdian, the beam is automatically gated — on when the tumour is in position, paused if it moves out. On Unity, cine MRI provides continuous monitoring throughout.

6. 6

   Post-Session Review and Dose Accumulation Tracking

   After each session, cumulative dose to the tumour and critical structures is tracked. This informs adaptation decisions for the next session and ensures organ dose limits are not exceeded over the full course.

MR-LINAC offers the greatest clinical advantage where conventional radiation is challenged by poor tumour visibility on CT, proximity to critical organs, or significant tumour motion during treatment.

• Pancreatic Cancer — The Flagship Indication

  The pancreas moves with breathing and is surrounded by the duodenum, stomach, bowel, and bile duct. Conventional SBRT requires large safety margins that limit achievable dose. MR-LINAC's real-time gating and daily adaptation enables dose escalation to ablative levels. The SMART trial delivered 50 Gy safely — a landmark result demonstrating what MR-LINAC can achieve where conventional SBRT cannot.

• Prostate Cancer

  The prostate moves with rectal filling and bladder volume changes between and during sessions. MRI provides superior prostate visualisation versus CT. The SHARP trial and multiple prospective series confirm excellent 2-year biochemical control with favourable toxicity — potentially fewer urinary and rectal side effects due to tighter margins.

• Rectal Cancer

  MR-LINAC enables neoadjuvant short-course SBRT (5 fractions) with daily adaptation. The STELLAR trial protocol delivers high-dose radiation with excellent soft tissue visualisation of the mesorectal fascia and adjacent bowel. High pathological complete response rates have been reported — a strong predictor of long-term outcomes.

• Liver Cancer and Liver Metastases

  MR-LINAC's real-time gating locks beam delivery to the breathing cycle, ensuring radiation only reaches the liver tumour at the correct position. Daily adaptation accounts for liver shape and tumour volume change. Prospective studies report 80–95% 2-year local control for liver targets — superior to conventional CT-guided SBRT in adjacent-organ situations.

• Cervical Cancer

  The cervix and uterus change substantially in position and shape during treatment. EMBRACE-II and MR-Linac Consortium trials are exploring whether MR-LINAC can complement or replace brachytherapy — potentially broadening access to optimally dosed treatment in settings where brachytherapy equipment is unavailable.

• Lung, Kidney, and Emerging Sites

  Lung SBRT with MR-LINAC allows real-time motion management without breath-hold — particularly valuable for patients with poor lung function. Renal cell carcinoma in solitary kidneys benefits from the tight dose constraints enabled by daily adaptation. Active investigation continues for head and neck, bladder, oesophagus, and bone metastases.

Understanding how MR-LINAC relates to other radiation platforms helps patients and clinicians make informed choices. The right technology depends on tumour site, clinical context, and centre expertise.

Selected efficacy data from published trials and prospective studies.

• ~80%1-Year Local Control — Pancreatic CancerSMART trial (MRIdian): 50 Gy in 5 fractions — ablative dose previously not achievable safely with conventional SBRT.
• 80–95%2-Year Local Control — Liver TargetsProspective MR-LINAC series for HCC and liver metastases with daily adaptation and real-time gating.
• ~100–150MR-LINAC Systems Installed Globally (2025)Concentrated at major academic cancer centres — less widely available than conventional LINAC.
• 45–90 minPer-Session Treatment Timevs 10–20 min for conventional LINAC — offset by only 3–5 total fractions vs 20–35 for conventional RT.

Eligibility requires a detailed clinical assessment by a radiation oncologist experienced with MR-guided adaptive therapy. These are general factors — individual assessment is mandatory.

MR-LINAC is among the most technology-intensive radiation platforms. Costs vary by country, indication, and number of fractions. All figures are indicative — confirm directly with the treating centre.

A comprehensive workup is required before MR-LINAC treatment can be planned. For patients coordinating care internationally, assembling this information in advance is critical to avoiding delays.

MR-LINAC side effects are similar in type to conventional SBRT at the same site. The adaptive precision may reduce severity by enabling tighter margins — but does not eliminate side effects. Individual risk depends on tumour location, dose, and adjacent anatomy.

• Fatigue

  Universal across all treatment sites. Accumulates across the treatment course and typically resolves within 2–4 weeks of completion. Managing energy and rest during treatment helps.

• Pancreas: GI Effects

  Nausea, mild epigastric discomfort, and transient enzyme elevation during treatment. Late risks include duodenal or gastric ulceration (reduced by MR-LINAC precision) and biliary stricture (rare).

• Prostate: Urinary and Rectal

  Urinary frequency, urgency, and mild rectal discomfort during and shortly after treatment. Generally less common than conventional LINAC-based SBRT due to tighter margins enabled by MRI guidance.

• Liver: Hepatic Effects

  Fatigue, mild nausea, and temporary liver enzyme elevation. Late risk of radiation-induced liver disease — particularly with underlying cirrhosis. Bile duct injury possible if close to treatment volume.

MR-LINAC is a specialised technology available at approximately 100–150 centres globally. Identifying the right centre for the right indication — and reaching it — requires informed navigation.

1. 1

   Medical Report and Imaging Review

   We review pathology, imaging, prior treatment records, and molecular profiling to assess whether MR-LINAC offers a meaningful advantage for the specific tumour site and clinical situation.

2. 2

   Centre Identification and Indication Matching

   We identify MR-LINAC centres with genuine expertise in the relevant indication — pancreatic SBRT, prostate SBRT, liver SBRT — not just those with a machine installed.

3. 3

   Specialist Consultation Facilitation

   We facilitate remote consultations and case presentations to radiation oncology teams with MR-LINAC experience, with translated medical records transmitted in advance.

4. 4

   Clinical Trial Identification

   We search for relevant open MR-LINAC trials — SMART protocol extensions, SHARP follow-on studies, MR-Linac Consortium registries — where trial participation may improve access and outcomes.

5. 5

   Full International Logistics Coordination

   Documentation, translation, visa support, travel planning, accommodation near the treating centre, and in-country support during the 3–5 week treatment period.

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Frequently Asked Questions