Reduced long-term side effects with MRI-guided radiotherapy in prostate cancer

Abstract

Magnetic resonance imaging (MRI)–guided stereotactic body radiotherapy (SBRT) for the treatment of prostate cancer reduces long-term gastrointestinal and genitourinary toxicity compared to computed tomography (CT)–guided SBRT after 2 years of treatment and is linked to less deterioration of bowel and sexual function according to a prespecified secondary analysis of the phase 3 MIRAGE trial published in European Urology.¹

The results provide longer term data at 2 years after treatment on the incidence of physician-scored toxicity and patient-reported quality-of-life measures after MRI-guided radiotherapy versus CT-guided radiotherapy.

Previous results of the MIRAGE trial showed that MRI-guided radiotherapy, which included an aggressive reduction in the planning treatment margin from 4 mm (used with CT-guided radiotherapy) to 2 mm, significantly lowered rates of acute genitourinary and gastrointestinal toxicities scored by physicians as higher than grade 2 and lowered patient-reported deterioration of urinary and bowel quality of life in the first 3 months following treatment.²

At 2 years, MRI-guided SBRT significantly reduced the incidence of late grade 2 or higher genitourinary toxicity (27% vs. 51%, p = .004) and gastrointestinal toxicity (1.4% vs. 9.5%, p = .02) versus CT-guided SBRT.

Clinically relevant deterioration of urinary irritation with MRI-guided SBRT also was reported by patients (14 of 73 vs. 24 of 68, p = .03), as was deterioration of bowel function (19 of 72 vs. 30 of 71, p = .04).

“This work supports the use of MRI-guided stereotactic body radiation therapy with tight margins for men with clinically localized prostate cancer to reduce posttreatment adverse effects,” says Gianluca Giannarini, MD, associate editor of European Urology.

Commenting on the study, Walter M. Stadler, MD, Chief Clinical Officer for City of Hope, Chicago, says that although the results are promising, there are several issues that limit the applicability of MRI-guided SBRT. He says that SBRT versus current short-course radiotherapy for localized prostate cancer is not yet considered standard treatment for most patients with localized prostate cancer. Another issue is that the assessment of toxicity in the study was based on physician assessment—not patient derived—and this could be potentially biased.

“Finally, the increased cost and technology requirements for MRI-guidance means that the vast majority of centers do not have this capacity,” he says.

Given these issues, he thinks that “this is not yet appropriate for general practice.”