MRI-guided RT reduced acute toxic effects in men with localized prostate cancer

MRI-guided stereotactic body radiation therapy (SBRT) for localized prostate cancer resulted in fewer toxicities and improved quality of life compared to CT guidance, according to the randomized phase III MIRAGE trial.

At 3-month follow-up, the incidence of grade 2 or greater acute genitourinary toxicity was 24.4% with MRI-guided SBRT versus 43.4% with CT (P= 0.01), while the incidence of grade 2 or greater acute 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.

Additionally, a significantly lower proportion of patients had an increase of 15 or more points in the International Prostate Symptom Score (IPSS) at 1 month with MRI guidance (6.8% vs 19.4%, P=0.01), whereas 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 (decrease in 4.1 points against 18.2 points, P<0.001), and there was a significantly higher proportion of patients treated with CT with a clinically relevant decrease (≥12 points) in EPIC-26 gut domain scores (50% versus 25%, P=0.001) at 1 month.

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

“Our results demonstrated that the aggressive margin reduction offered by MRI guidance resulted in a substantial reduction in physician-rated acute toxic effects as well as multiple patient-reported outcome parameters,” Kishan et al. his team.. “Longer-term follow-up is needed to determine if differences in late urinary or intestinal toxic effects will occur and to assess differences in sexual outcomes.”

In explaining the rationale for the study, Kishan and colleagues noted that MRI guidance offers a number of advantages over CT guidance, particularly the ability to reduce planning margins and provide more treatment. targeted, thereby reducing the toxic effects of the treatment on nearby organs and tissues. .

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

In a commentary accompanying the studyShankar Siva, PhD, MBBS, of the Peter MacCallum Cancer Center in Melbourne, and colleagues wrote that the MIRAGE trial “demonstrated clear clinical benefit by implementing an exciting new technology.”

However, they also noted that the data offers “interesting insights” into how doctors assess toxicity versus how patients report adverse events.

“Data noted by the physician show that the likelihood of developing toxicity is lower in the MRI group during the first 90 days after radiation therapy. However, this is where the PROs [patient-reported outcomes] the data offer different perspectives. Although MRI-based SBRT provided benefit in some PRO subdomains, this difference was primarily observed within the first month and largely resolved by the 3-month follow-ups,” they wrote.

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

Siva and colleagues further noted that Kishan’s group estimated the cost differential for the MRI-guided strategy to be around $1,500, and thus “until a full 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 his team enrolled men with histologically confirmed and clinically localized prostate cancer (median age 71 years) from a single center from May 2020 to October 2021. Patients were randomized 1 : 1 for 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.