Toxicity lower with MRI-guided vs CT-guided RT in prostate cancer

Results from the phase MIRAGE trial reported at the 2022 ASTRO Annual Meeting suggest that MRI guidance is more advantageous than CT guidance in reducing genitourinary (GU) and gastrointestinal (GI) side effects of stereotactic body radiotherapy (SBRT).1,2

The findings showed a 43.4% rate of acute grade >2 GU toxicity for CT-guided SBRT in comparison to a 24.4% rate of acute grade >2 GU toxicity for MRI-guided SBRT with the MRIdian MRI system (ViewRay). The researchers added that a subsequent multivariable analysis—accounting for differences in prostate size, baseline urinary symptoms and use of a hydrogel spacer—revealed a 60% reduction in the risk of grade >2 GU toxicity with MRI guidance.

In the study, which involved 156 patients, the authors indicated that none of the patients in the MRI group had acute grade >2 GI toxicity in comparison to a 10.5 % toxicity rate in the CT group.

In regard to patient-reported outcomes with prostate SBRT, the incidence of increased urinary symptoms measured by the International Prostate Symptom Score was 12.6 % lower in the MRI guidance group, according to the study. The researchers also noted that half of the patients in the CT guidance group reported a decrease in bowel-related quality of life in comparison to 25 % of those who had MRI-guided SBRT.

With these study results, Amar Kishan, MD, a co-author of the study, said he and his colleagues at UCLA have shifted to nearly “exclusive” use of MRI-guided prostate SBRT after offering CT-guided prostate SBRT since 2010.

“A major consideration with prostate SBRT is the margin of normal tissue around the target that is exposed to high-dose radiation. The highly positive final results of our phase III MIRAGE trial show that when MRI guidance is used to shrink that margin, there are significant improvements in both physician-scored and patient-reported toxicity in terms of urinary and bowel side effects,” noted Kishan, an associate professor and chief of the Genitourinary Oncology Service at UCLA.


1. Kishan AU, Ma TM, Lamb JM, et al. Magnetic Resonance Imaging-Guided vs. Computed Tomography-Guided Stereotactic Body Radiotherapy for Prostate Cancer (MIRAGE): Primary Endpoint Analysis of a Phase III Randomized Trial. Int J Radiat Oncol Biol Phys.114(3):S92-S93. doi: 10.1016/j.ijrobp.2022.07.507

2. MIRAGE Phase III Randomized Controlled Trial Demonstrates Superiority of MRIdian® MRI-Guidance in Stereotactic Body Radiotherapy (SBRT) for Localized Prostate Cancer. Published online October 27, 2022. Accessed November 2, 2022.