MR-LINAC: Advanced Radiation Therapy

Introduction

MR-LINAC (Magnetic Resonance Linear Accelerator) represents one of the most significant innovations in modern radiation oncology. This technology integrates high-resolution MRI imaging with a linear accelerator, enabling clinicians to visualize tumors in real time during radiation delivery.

Unlike conventional radiotherapy, where imaging is typically performed before treatment, MR-LINAC allows continuous soft-tissue visualization throughout each session. This enables adaptive, highly personalized treatment.

Despite its clinical potential, MR-LINAC remains a relatively rare technology. In Spain, there are currently only a handful of operational systems, approximately four centers, highlighting its exclusivity and technological complexity. One of the leading institutions offering this technology is the Quirónsalud Proton Therapy Center in Madrid.

What Is MR-LINAC?

MR-LINAC combines two advanced technologies:

• MRI scanner — provides high-contrast imaging of soft tissues
• Linear accelerator (LINAC) — delivers radiation therapy

This integration allows for:

• Real-time tumor tracking
• Daily treatment adaptation (adaptive radiotherapy)
• Precise targeting while sparing healthy tissues

The most widely used systems are developed by companies such as Elekta (Unity MR-Linac) in collaboration with Philips for MRI technology.

Advantages Over Standard Radiation Therapy

1. Real-Time Imaging During Treatment

One of the defining features of MR-LINAC is continuous visualization of the tumor and surrounding organs during radiation delivery.

This allows clinicians to:

• Monitor tumor motion (e.g., due to breathing or organ filling)
• Interrupt or adjust treatment if the tumor moves
• Ensure radiation is delivered only when the target is correctly positioned

2. Synchronization With Tumor Position

MR-LINAC enables gating and tracking, meaning radiation can be synchronized with the tumor’s exact position in real time.

This is especially important for:

• Prostate cancer
• Pancreatic tumors
• Liver and lung lesions

3. Adaptive Radiotherapy (ART)

Each treatment session can be adjusted based on daily anatomical changes:

• Tumor shrinkage
• Organ movement
• Changes in surrounding tissues

This process is known as online adaptive radiotherapy, which improves accuracy and safety.

4. Increased Precision and Reduced Toxicity

Because MR-LINAC provides superior soft-tissue contrast:

• Smaller safety margins are needed
• Less healthy tissue is irradiated
• Potential side effects may be reduced

5. Fewer Treatment Sessions (Hypofractionation)

One of the most impactful benefits is the ability to deliver higher precision doses per session.

For example:

• Traditional prostate radiotherapy: ~20 sessions
• MR-LINAC-based treatment: 3–5 sessions in selected cases

This approach is often referred to as stereotactic body radiotherapy (SBRT).

MR-LINAC vs Proton Therapy

Both MR-LINAC and proton therapy represent advanced forms of radiation therapy, but they differ fundamentally in their physical principles and clinical applications.

Key Differences

Clinical Considerations

• MR-LINAC excels in cases where tumors move or are close to critical organs
• Proton therapy may be advantageous for reducing dose to surrounding tissues, especially in pediatric or complex anatomical cases

These technologies are not competitors but complementary tools. The choice depends on:

• Tumor type and location
• Patient-specific anatomy
• Clinical goals

Treatment decisions are always individualized and made by a multidisciplinary medical team.

MR-LINAC at Quirónsalud Proton Therapy Center

The Quirónsalud Proton Therapy Center in Madrid represents a unique example of integrating two of the most advanced radiation technologies:

• MR-LINAC (Elekta Unity system)
• Proton therapy

This strategic combination allows:

• Tailored treatment selection
• Access to both photon-based adaptive therapy and proton therapy
• Multidisciplinary expertise in one location

Technology Platform

The center utilizes:

• Elekta Unity 1.5T MR-LINAC
• MRI integration by Philips

This system enables full implementation of online adaptive radiotherapy workflows, including:

• Adapt-to-Shape (ATS)
• Adapt-to-Position (ATP)

Clinical Leadership: Dr. Walter Vasquez

The MR-LINAC program at Quirónsalud is led by Walter Vasquez Rivas, Radiation Oncologist and Clinical Lead for the MR-Linac Unity program.

Dr. Vasquez brings:

• Over 8 years of clinical experience in radiation oncology
• Leadership in MR-LINAC commissioning and program development
• Expertise in adaptive radiotherapy and SBRT
• Specialization in genitourinary cancers, including prostate cancer

He is actively involved in:

• Daily adaptive treatment planning
• Multidisciplinary case evaluation
• Development of clinical protocols

Additionally, Dr. Vasquez has participated in international MR-LINAC training and collaborations, including advanced clinical observerships in specialized centers.

His work focuses on delivering high-precision, patient-centered care, particularly for international patients.

Modern Research and Future Perspectives

MR-LINAC is an evolving technology with ongoing clinical research in:

• Adaptive radiotherapy protocols
• Dose escalation strategies
• Hypofractionation
• Integration with systemic therapies

Organizations such as:

• European Society for Radiotherapy and Oncology (ESTRO)
• National Comprehensive Cancer Network (NCCN)

continue to evaluate its role in clinical guidelines.

While early data are promising, long-term outcomes are still being studied.

When to Consider MR-LINAC

MR-LINAC may be considered in cases where:

• Tumors are located near critical organs
• Tumor motion is significant
• High precision is required
• Fewer treatment sessions are desirable

Examples include:

• Prostate cancer
• Pancreatic tumors
• Liver metastases
• Oligometastatic disease

A detailed evaluation by a radiation oncologist is required to determine suitability.

Conclusion

MR-LINAC represents a major advancement in radiation therapy by combining real-time imaging with adaptive treatment delivery. It offers improved precision, potential reduction in treatment sessions, and enhanced personalization.

When available in specialized centers such as Quirónsalud Proton Therapy Center, it can be part of a broader strategy that includes proton therapy and other advanced techniques.

As with all cancer treatments, the optimal approach depends on individual patient factors and should be determined by experienced multidisciplinary teams.