For select patients with difficult-to-treat tumors, MR-guided radiation therapy is changing what is possible in radiation oncology. By combining high-resolution magnetic resonance imaging with radiation delivery in a single system, MR Linac technology allows the care team to visualize anatomy in real time, adapt the treatment plan to the patient’s anatomy of the day and verify positioning before and during treatment.

At Baptist Health Cancer Care, Kathryn Mittauer, PhD, senior medical physicist at Baptist Health Herbert Wertheim Cancer Institute, and Michael Chuong, M.D., vice chair and medical director of radiation oncology at Baptist Health Herbert Wertheim Cancer Institute, lead this approach. The technology is intended for tumors in the abdomen, where the stomach, bowel and other organs can shift from day to day — and even during a treatment session.

For patients with locally advanced pancreatic cancer, MR-guided online adaptive radiation therapy can help physicians deliver an ablative dose to the tumor while carefully protecting nearby gastrointestinal organs.

“Online adaptive MR-guided radiation is a very team-oriented treatment,” said Dr. Chuong. “There are many factors within the workflow, including the physician, physicist and radiation therapists. The goal is to drive both efficiency and quality.”

Below, Baptist Health Cancer Care has crafted an educational step-by-step video for medical physicists and radiation oncologists who are interested in learning and adopting online adaptive radiotherapy into their practice.

As dictated by both Drs. Mittauer and Chuong, a full step-by-step has been crafted for reference.

Step 1: Patient Selection and Treatment Planning

The process begins before the patient enters the treatment room. For locally advanced pancreatic cancer, patients often receive chemotherapy first. If there is no evidence of distant metastasis, radiation therapy may be considered as part of a multidisciplinary treatment approach.

In the MR Linac workflow demonstrated by the Wertheim Cancer Institute team, the patient is treated with an ablative five-fraction regimen using a simultaneous integrated boost. The visible gross tumor receives 50 Gy in five fractions, while the elective nodal volume receives 33 Gy in five fractions. Treatment is delivered on consecutive days using MR-guided online adaptation.

This treatment strategy is designed for precision. The goal is not simply to reproduce the original plan each day, but to account for the patient’s anatomy at the time of treatment.

Step 2: Patient Setup

Once the patient is brought into the treatment room, the team positions the patient comfortably on the treatment table. In the demonstrated abdominal workflow, no immobilization is used. The patient lies with arms down by the sides, supported by a pad and abdominal coils.

This differs from many conventional radiation approaches, where reproducibility from day to day is heavily dependent on immobilization. With MR-guided adaptive radiotherapy, the team can image the patient immediately before treatment and adapt the plan to the anatomy of the day, reducing the reliance on rigid setup reproducibility.

Step 3: Image Acquisition

The adaptive workflow begins with image acquisition. The patient completes a breath hold while a fast balanced MRI scan is obtained. In the demonstrated workflow, this scan takes approximately 25 seconds.

The image of the day is then compared with the simulation image. The treatment team performs tumor-to-tumor localization, aligning the gross tumor volume from the simulation image with the tumor seen on the daily MR image.

Before moving forward, the team also checks the skin and field of view. This is a critical quality step because a new plan will be generated from the day’s anatomy. If patient anatomy is cut off, dose calculation accuracy can be affected.

Step 4: Physician, Physicist and Therapist Begin Parallel Contouring

After alignment is approved, the team begins a parallel workflow. The physician, physicist and radiation therapists work simultaneously from separate, integrated workstations.

The therapist contours the tracking structure that will later be used for motion monitoring. The physician contours the targets and clinically relevant organs at risk. The physicist updates electron density assignments and reviews structures such as kidneys, spinal canal and other necessary anatomy.

The parallel structure is important because online adaptive radiotherapy is time sensitive. Internal anatomy, especially gastrointestinal anatomy, can continue to change because of peristalsis and other motion. Efficiency helps ensure that the treatment plan reflects the anatomy as close as possible at the time of delivery.

Step 5: Contour the Anatomy That Matters Most for Decision-Making

In online adaptation, contouring is not about making every structure visually perfect. It is about accurately defining the anatomy that will influence dose delivery and clinical decision-making.

For pancreatic treatments, the gastrointestinal luminal organs are especially important because they are often the dose-limiting organs at risk. The physician focuses on the stomach, duodenum, bowel and other structures close enough to the target to affect whether the plan needs to be adapted.

One common pitfall is under-contouring the gastrointestinal organs. The team emphasizes that the entire wall of the organ should be included, not just the bright fluid or contents inside the lumen. In areas with motion artifact or uncertainty, the physician may contour slightly more generously to avoid missing clinically relevant anatomy.

This is especially important near the pylorus and first portion of the duodenum, where gastrointestinal toxicity, though uncommon, is most likely to occur.

Step 6: Update Electron Density Assignments

For abdominal MR-guided adaptive treatments, the team uses a bulk-density, MR-only approach. The physicist updates density assignments based on the daily MR image. This includes gastrointestinal air, bone, and any lung depending on the anatomy present within the adaptive contouring region.

This step allows the team to calculate dose on the day’s anatomy, even though the workflow is MR-based.

Step 7: Build Adaptive Planning Structures

Once the contours are reviewed, the planning system applies institutional planning rules. For pancreatic treatments, the team uses structures that help maintain target coverage while protecting gastrointestinal organs.

The workflow includes creating combined gastrointestinal organ at risk contours and a gastrointestinal planning organ at risk volume. The gross tumor volume and clinical target volume are cropped based on the gastrointestinal luminal wall. Optimization structures are then used to drive full dose to portions of the target not overlapping with organs at risk.

Additional structures, including PTV expansions and ring structures, help control dose conformity and the 50 percent isodose region. These rules help standardize the adaptive process across treatment days and across cross-covering physicians and physicists who may be covering the case.

Step 8: Generate and Review the Adaptive Plan

The system generates a fully reoptimized adaptive plan based on the patient’s anatomy and contours of the day. The team compares this with the predicted plan, which is the original plan recalculated on the current anatomy.

This comparison helps answer a key clinical question: Is the original plan still acceptable today, or does the patient benefit from adaptation?

The physicist first evaluates plan modulation and performs normalization and/or reoptimization based on the closest organ(s) at risk. The plan is reviewed for organ at risk constraints, target coverage, dose distribution, conformity and quality assurance metrics.

The physician then reviews the adaptive plan with the physicist. Together, they examine hotspots, isodose lines and the relationship of high-dose regions to sensitive organs, anticipating the possibility of small anatomic shifts during treatment.

Standardizing the visual review process, including the colors of numerical isodose lines, helps the team make these decisions efficiently and consistently.

Step 9: Verification Imaging Before Treatment Delivery

Before radiation delivery begins, the team performs verification imaging. In the demonstrated workflow, the patient is monitored using a single sagittal MR plane acquired at eight frames per second.

The tracking contour is reviewed with a three-millimeter expansion that represents the acceptable gating boundary. The therapist and physicist confirm that the tumor and surrounding stomach and bowel still match the anatomy used for the adapted plan. If the anatomy has changed, the team may perform another three-dimensional volumetric scan, shift the patient or readapt the plan, depending on the degree and clinical significance of the motion.

Step 10: Gated Radiation Delivery With Continuous Monitoring

Once verification is complete, treatment begins. The patient uses visual feedback, such as a monitor with a target display, to guide breath holds. Radiation is delivered only when the anatomy is within the defined gating boundary.

The patient holds their breath as long as comfortably possible and breathes freely between holds. The team coaches the patient throughout treatment, helping them return to the appropriate position for gated delivery.

If anatomy moves during treatment, the team can pause delivery, reimage and determine whether a shift or readaptation is needed. This continuous monitoring is one of the major advantages of MR-guided radiation therapy.

Why the Workflow Matters

MR Linac treatment is not a single action but a coordinated sequence of imaging, contouring, planning, verification and delivery. Each step depends on the expertise of the physician, physicist and radiation therapists working together in real time.

“From a physics perspective, the strength of MR-guided adaptive therapy is that it allows us to evaluate the patient’s anatomy in the moment and make informed adjustments before treatment is delivered,” said Dr. Mittauer. “That level of precision is especially important when we are treating tumors close to organs that can move or change position from day to day.”

For patients with tumors near sensitive organs, this can make a meaningful difference. The ability to adapt treatment to the anatomy of the day allows the team to pursue highly conformal, dose-escalated radiation while maintaining careful attention to safety.

For referring physicians, the key takeaway is that MR-guided online adaptive radiotherapy may be an important option for selected patients whose tumors are difficult to treat with conventional approaches because of proximity to the stomach, bowel or other critical structures.

“This workflow gives us the opportunity to personalize treatment each day rather than relying only on a static plan created before therapy begins,” said Dr. Chuong. “For carefully selected patients, that can help us safely intensify treatment while maintaining a strong focus on protecting normal tissue.”

As MR-guided radiation therapy continues to evolve, the focus remains the same: delivering the right dose to the right target at the right time, while protecting the normal tissues that matter most.

For more information regarding radiation oncology offered at Herbert Wertheim Cancer Institute, visit here.