MR Linac

What is MR Linac?

The MR Linac (MRL), also known as MRI-guided Linac, is the most advanced form of image-guided radiotherapy currently available. It uniquely combines high-resolution MRI scanning with a linear accelerator, allowing doctors and radiographers to visualise the prostate and surrounding tissues in real time as the radiotherapy is being delivered. For men with prostate cancer, this innovation means greater precision, fewer side effects, and the possibility of shorter treatment courses.

Why use MR Linac for prostate cancer?

The prostate is a small gland located close to several sensitive structures, including the rectum and bladder. These organs can shift position daily, influenced by bowel filling, bladder volume, or even slight changes in posture. Conventional radiotherapy must account for this variability by expanding the treatment margins, which can inadvertently expose healthy tissues to radiation.

MR Linac’s live MRI imaging provides a much clearer view of the prostate and its surrounding structures than CT. This allows for:

• Precise targeting of the cancer, even if the prostate moves during treatment.
• Smaller safety margins, reducing radiation exposure to the rectum and bladder.
• Real-time plan adaptation—the treatment plan can be adjusted on the spot based on the prostate’s position that day. 

Treatment on the MR Linac

A typical course of prostate radiotherapy used to require 20–37 daily sessions. With MR Linac, many patients can be treated with just five sessions. This type of treatment is called stereotactic ablative radiotherapy (SABR).

Each session on the MR Linac takes about 45–60 minutes, compared to 10–15 minutes with conventional radiotherapy. This is because of the extra steps involved, including:

• A daily MRI scan before treatment to assess anatomy.
• On-the-day plan adaptation by the clinical team.
• Real-time tracking and automatic pausing of the beam if the tumour moves.

This level of precision ensures that the radiation dose is delivered exactly where it’s needed, every time. 

Benefits of MR Linac for prostate cancer

• Exceptional accuracy: the prostate is visualised clearly each day, and treatment is adjusted accordingly.
• Fewer side effects: by avoiding healthy tissue, patients experience fewer urinary and bowel symptoms.
• Simultaneous Integrated Boost (SIB): MR Linac allows clinicians to give a higher dose to the most aggressive part of the tumour without increasing side effects.
• Treatment flexibility: suitable for patients who have already had prostate radiotherapy or those seeking fewer treatment visits.

In a study conducted at VU University Medical Centre in Amsterdam, patient-reported side effects with MR Linac were low, particularly regarding bowel and urinary symptoms. 

Who can have MR Linac radiotherapy?

Not all prostate cancers are suitable for MR Linac treatment.

Factors that influence eligibility include:

• Prostate size
• Urinary symptoms
• Prior radiotherapy history
• Ability to lie still for up to an hour

Your suitability will be assessed by a multidisciplinary team, including oncologists and urologists, who will tailor a personalised treatment plan.

It’s important to inform your clinical team if you have pacemakers, surgical clips, or joint replacements, as some may not be MRI-compatible. Patients with claustrophobia should also inform the team in advance, as strategies such as relaxation techniques or mild sedatives may be helpful. 

What to expect during treatment

Planning appointment:

• Lasts around 2 hours.
• Involves MRI and CT scans in treatment position.
• You will be asked to attend with a comfortably full bladder.

Treatment sessions:

• Occur over five consecutive or more frequently on alternate days.
• Each day starts with an MRI to assess internal anatomy.
• Treatment plan is adapted in real time.
• The beam automatically pauses if your prostate moves.
• You can return home after each session. 

Side effects

Thanks to its accuracy, MR Linac radiotherapy is associated with fewer and milder side effects than traditional radiotherapy.

Common short-term effects may include:

• Mild discomfort or urgency when urinating.
• Loose or more frequent bowel movements.
• Tiredness.