Reno Cancer Center

Prostate radiation (MRI-guided)

1–2 minutes
This time-lapse video (played at 4x speed) of real-time MRI imaging of the pelvis in the sagittal plane during treatment shows significant deformation of the prostate as a result of bowel gas distending the rectum.

MRI-guided radiation

Prior to going bankrupt in 2023, the ViewRay MRI Linac was making waves in real-time target visualization during radiation treatment. Previously difficult moving organs to treat in the abdomen such as the pancreas and liver could now be clearly seen on MRI and tracked to only deliver radiation when the cancer was in the target volume.

Prostate SBRT seemed like a natural use case for this new technology as well. The team at UCLA ran the MIRAGE trial, comparing the ViewRay system to a Truebeam C-arm Linac. Now, the ViewRay system is limited in the number of beam angles that can be delivered, making a high dose gradient harder to achieve. However, the superior imaging allowed the planned margin for error to be reduced to 2mm around the prostate. The trial specified a 4mm margin around the Truebeam treated patients. The median treatment time was 19 minutes for the ViewRay vs 3 minutes for the Truebeam.

In addition to reducing the proportion of men needing medication for increased urethra/bladder irritation, none of the 78 patients treated on ViewRay had diarrhea vs 8 of the 76 patients treated on Truebeam. Another advantage of the MRI-Linac is it doesn’t require fiducial seeds to be placed into the prostate. I’ve heard ViewRay systems are still being supported by private equity. Elekta also makes an MRI-Linac, so hopefully this technology will continue being developed and available for patient care.