In a webinar entitled UCLA clinical experience with MRI-guided adaptive radiotherapy: stereotactic body radiotherapy (SBRT)/stereotactic ablative radiotherapy (SABR) for abdominal tumors and accelerated partial breast radiotherapy (APBR) for breast cancer, doctors from the David Geffen School of Medicine at UCLA shared their insights regarding first-person experience with ViewRay’s MRIdian.

MRIdian is the only clinical MR-guided radiation therapy system in the world that allows clinicians to observe, assess and personalize a patient’s treatment. Clinicians can see soft tissue, visualize and adjust the dose, and gate therapy in real time.

Dr. Michael Steinberg, professor and chair of the department of radiation oncology at UCLA, moderated the seminar, which included presentations by Dr. Percy Lee, associate professor of radiation oncology, and Dr. Philip Beron, assistant clinical professor of radiation oncology.
Lee discussed current challenges in abdominal tumors, specifically liver and pancreas, using cone beam CT-based image-guided radiation therapy, and spoke on how cone beam CT has severe limitations in the abdomen/pelvis in terms of inability to differentiate between normal tissue and target tissue in a patient.

“Many will appreciate the difference in contrast in soft tissue in the MR and the CT, which in theory, will allow for better targeting, better treatment, better gating and new ability to perform adaptive therapy in real time,” Lee said.

Beron discussed MRIdian for use in assessing possible disease spread with accelerated partial breast radiotherapy, with regard to clinical target volume, which is the imaged tumor and some surrounding tissue; and planning target volume, which ensures that the radiotherapy dose is actually delivered to the correct area.

“With the comparison of clinical target volume (CTV) and planning target volume (PTV), we do not use the PTV, because PTV is for position setup error or uncertainty. Since we’re monitoring the cavity throughout the treatment, we have eliminated that uncertainty,” said Beron.

Beron also discussed how physicians can see the treatment live to help reduce certain errors that are known to happen with CT-based treatment. He showed two images of the same patient’s lesion using CT and MR imaging to compare them, and said, “Although the CT scan is somewhat acceptable, there is muddying along the chest wall musculature and the image clearly is superior on the MR.”

In another example, he explained how the CT image, because of some densities in the breast, made it difficult to accurately distinguish the resection cavity that might be removed. However, in the MR image, the resection cavity is clear.

MRIdian received FDA approval in 2012, and CE mark in 2014.

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