Innovations in Cancer Care: MRI-Guided Radiotherapy and Compact Proton Beam Radiation

In the past year, radiation oncologists at the Alvin J. Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine have treated a select group of patients with two novel radiation-therapy technologies: MRI-guided radiotherapy and compact proton beam therapy.

MRI-Guided Radiotherapy

More than 115 patients have been treated at Siteman Cancer Center with ViewRay, the world’s first radiotherapy system guided by magnetic resonance imaging (MRI). Developed by a Washington University physicist and tested by oncologists at Siteman Cancer Center, the system has proven its ability to precisely target tumors and significantly reduce treatment margins in breast cancer patients, the largest group of patients treated to date.

An MRI scan generates clearer, more detailed views of internal organs than computed tomography (CT) scans, making it ideal for use in treating cancers of the abdomen, head and neck, and breast. By combining continuous MRI with a sophisticated radiation delivery system, specialists can track and observe almost immediate changes in the location of the tumor during treatment.

“The system’s real value is seen when we gate, or set treatment margins around a tumor,” says Sasa Mutic, PhD, director of medical physics in the Department of Radiation Oncology. “Typically, we set margins wide to account for any movement of the tumor during radiation,” he says, noting that surrounding healthy tissue also receives radiation. “With the MRI-guided system, we can plan tighter treatment margins; if the targeted tumor moves beyond prescribed boundaries when the patient breathes or during other movement, the system shuts off until the tumor returns to the targeted treatment site.”

As a result, margin reductions have been significant. Radiation oncologist Maria Thomas, MD, PhD, analyzed the benefits of the new radiotherapy system over the past year, specifically for patients with early-stage breast cancer receiving partial breast radiation.

“Because we can see the surgical cavity in the breast quite well with MRI, we are able to reduce any additional margin and treat only the target volume,” Thomas says. “This translates to a reduction in unnecessary radiation exposure to adjacent normal breast tissue and structures such as the skin, ribs, lung and heart.” She notes that, with MRI-guided treatment, the mean volume of tissue receiving a prescription dose has been reduced by approximately 50 percent.

Mutic notes that data is still coming in. “The next challenge is to better define the use of adaptive radiotherapy (ART) and determine when we should deliver more radiation doses or should shrink margins. I’m excited about the possibilities.”

Compact Proton Beam Therapy

A year ago, the S. Lee Kling Proton Therapy Center at Siteman became home to the world’s first compact proton accelerator. The system, called the Mevion S250, is markedly smaller than conventional proton therapy systems and costs significantly less to operate. To date, Siteman specialists have used it to treat more than 150 patients from Missouri and surrounding states.

“The compact system has surpassed our patient-volume expectations. We’ve used it to treat inoperable tumors that are particularly close to sensitive areas, such as the eyes, brain and spinal cord, and to treat solid tumors that haven’t spread,” says radiation oncologist Jeffrey Bradley, MD, director of the center. And he notes that, in the coming months, the center will install an in-treatment-room CT scanner, which will allow radiation therapists to improve patient positioning and tumor localization. “We think that adding the CT scanner to the mix will enhance the effectiveness of treatment,” Bradley says.

Clinical trials are underway to determine if the number of treatments per patient can be reduced without lowering effectiveness. “Right now, the number of proton treatments is the same as the number of treatments with traditional radiation therapy,” says Bradley. “In one trial, we’re looking at whether we can cut that number in half for patients with lung cancer and still be as effective.”

Bradley adds, “It can be a challenge to get insurance to support proton therapy treatments because they are often expensive. But our results with the smaller, more cost-effective proton system may eliminate that obstacle and open the door for more patients to receive this kind of therapy.”

Siteman Cancer Center is the only place in the world that has both compact proton beam therapy and MRI-guided radiotherapy, Bradley says. The center has a long history of innovation in radiation oncology. “We continue to define treatment parameters for these two technologies, which improve efficacy while reducing side effects.”

Published in Innovate Oncology, vol. V, summer 2015