Stereotactic body radiotherapy (SBRT) guided by MRI for localized prostate cancer resulted in fewer toxicities and an improvement in quality of life compared with CT guidance, according to the randomized phase III MIRAGE trial.

At 3-month follow-up, incidence of acute grade 2 or higher genitourinary toxic effects was 24.4% with MRI-guided SBRT versus 43.4% with CT guidance (P=0.01), while incidence of acute grade 2 or higher gastrointestinal toxic effects was 0% versus 10.5%, respectively (P=0.003), reported Amar U. Kishan, MD, of the University of California Los Angeles, and colleagues.

Moreover, a significantly smaller proportion of patients had a 15-point or greater increase in International Prostate Symptom Score (IPSS) at 1 month with MRI guidance (6.8% vs 19.4%, P=0.01), though this was not the case at 3 months (4.1% vs 1.4%, P=0.30), they noted in JAMA Oncology.

Among the 154 patients in the study, MRI guidance also resulted in a significantly smaller decrease in Expanded Prostate Cancer Index Composite-26 (EPIC-26) bowel domain subscores at 1 month (4.1-point vs 18.2-point decrement, P<0.001), and there was a significantly larger proportion of patients treated with CT guidance with a clinically relevant (≥12-point) decrease in EPIC-26 bowel domain scores (50% vs 25%, P=0.001) at 1 month.

The team also observed a numerically greater increase in EPIC-26 sexual domain scores that favored MRI guidance at 3 months.

“Our results demonstrated that the aggressive margin reduction afforded by MRI guidance allowed a substantial reduction in acute physician-scored toxic effects as well as multiple patient-reported outcome metrics,” Kishan and team wrote. “Longer-term follow-up is necessary to determine whether differences in late urinary or bowel toxic effects will occur and to evaluate differences in sexual outcomes.”

In explaining the rationale behind the study, Kishan and colleagues noted that MRI guidance offers a number of advantages over CT guidance, specifically the ability to reduce planning margins and provide a more focused treatment, thereby reducing the toxic effects of treatment to nearby organs and tissue.

However, “given the increased resources needed for MRI-guided radiotherapy, it is imperative to establish that it offers a tangible benefit for patients,” they added.

In a commentary accompanying the study, Shankar Siva, PhD, MBBS, of Peter MacCallum Cancer Centre in Melbourne, and colleagues wrote that the MIRAGE trial “demonstrated an undoubted clinical advantage by implementing exciting new technology.”

However, they also noted that the data offer “interesting insights” into the ways in which physicians evaluate toxicity compared with how patients report adverse events.

“The physician-scored data show that the likelihood of developing toxicity is lower in the MRI group during the first 90 days following radiotherapy. However, this is where the PROs [patient-reported outcomes] data offer some different insights. Although MRI-based SBRT offered an advantage in some PRO subdomains, this difference was predominantly observed in the first month and largely resolved by the time of the 3-month follow-ups,” they wrote.

“These findings lead us to ask how we, as a community, should value these improvements in early acute toxicity from a patient and payer perspective,” they added.

Siva and colleagues further noted that Kishan’s group estimated that the cost differential for the MRI-guided strategy was approximately $1,500, and thus “until a comprehensive cost-effectiveness analysis is completed, it is difficult for the community to estimate the value of potentially transient improvements in toxicity.”

For this study, Kishan and team included men with histologically confirmed, clinically localized prostate cancer (median age 71 years) from a single center from May 2020 to October 2021. Patients were randomized 1:1 to SBRT with CT guidance or MRI guidance. Planning margins of 4 mm (CT arm) and 2 mm (MRI arm) were used to deliver 40 Gy in 5 fractions.

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