Dr. Kishan on the MIRAGE Trial of MRI-Guided SBRT in Prostate Cancer

Amar U. Kishan, MD, associate professor, Vice-Chair, Clinical and Translational Research, chief, Genitourinary Oncology Service, Department of Radiation Oncology, David Geffen School of Medicine and the University of California, Los Angeles (UCLA) Jonsson Comprehensive Cancer Center, discusses interim results from the phase 3 MIRAGE trial (NCT04384770) of magnetic resonance imaging (MRI)–guided stereotactic body radiotherapy (SBRT) in prostate cancer.

This single-center, randomized trial tested MRI-guided SBRT against standard-of-care (SOC) computed tomography (CT)–guided SBRT for prostate cancer. The goal of this study was to assess whether MRI-guided SBRT can provide greater benefit to patients at the same radiation dose as standard CT-guided SBRT, Kishan begins. The study’s primary end point was the incidence of acute grade 2 or greater, physician-reported genitourinary (GU) toxicity. Physician-reported gastrointestinal (GI) toxicity and patient reported outcomes were also assessed, Kishan notes.

A prespecified interim analysis of the trial was conducted on October 1, 2021, and findings were subsequently in January 2023. Results showed that the use of MRI-guided SBRT resulted in a significant reduction in acute GU toxicity from 43.4% to 24.4%, while acute GI toxicity was reduced by 10.5%, Kishan states. Moreover, patient-reported urinary symptom burden decreased from 19.4% with CT-guided SBRT to 6.8% with MRI-guided SBRT at 1 month according to the International Prostate Symptom Scoring (IPSS) system. The IPSS consists of a 0- to 35-point scale, with 15 points as the classification threshold for significant symptom burden, Kishan explains.

Similarly, bowel symptom burden was assessed with the Expanded Prostate Cancer Index Composite-26 (EPIC-26) questionnaire, which has established thresholds for determining clinically relevant decrement in urinary incontinence, urinary irritative or obstructive, bowel, and sexual domains. Analysis of this questionnaire showed a clinically significant decrease in bowel symptom burden from 50% with CT-guided SBRT to 25% with MRI-guided SBRT, Kishan says.

Overall, results indicate that MRI-guided SBRT allowed for tighter planning margins, thereby facilitating a reduction in both physician-reported and patient-reported bowel and bladder toxicities, Kishan concludes.