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It has been shown that magnetic resonance imaging (MRI) guidance versus computed tomography (CT) guidance for aggressive margin-reduction (AMR) for stereotactic body radiotherapy (SBRT) in prostate cancer reduces acute toxicity, but the longer-term benefits are unknown. We performed a secondary analysis of MIRAGE, a phase 3 randomized clinical trial of MRI-guided SBRT for prostate cancer, to determine whether AMR with MRI guidance significantly reduced 2-yr physician-scored or patient-reported toxic effects in comparison to CT guidance. The cumulative incidence of 2-yr physician-scored toxicity, defined as grade ≥2 genitourinary (GU) and gastrointestinal (GI) toxic effects according to Common Terminology Criteria for Adverse Events v4.03, were lower with MRI guidance. Cumulative incidence rates of late grade ≥2 toxicity at 2 yr with MRI-guided versus CT-guided SBRT were 27% (95% confidence interval CI 19-39%)] versus 51% (95% CI 41-63%) for GU toxicity (p = 0.004), and 1.4% (95% CI 0.2-9.6) versus 9.5% (95% CI 4.6-19) for GI toxicity (p = 0.025). Cumulative logistic regression revealed that MRI-guided SBRT was associated with significantly lower odds of a clinically relevant deterioration in bowel function according to the Expanded Prostate Cancer Index Composite-26 score (odds ratio 0.444, 95% CI 0.209-0.942; p = 0.035) and in the Sexual Health Inventory in Men score (odds ratio 0.366, 95% CI 0.148-0.906; p = 0.03). There were no significant differences in the odds of a deterioration for other quality-of-life metrics. These findings support the hypothesis that aggressive planning for margin reduction for prostate SBRT using MRI leads to continued reductions in toxic effects over 2-yr follow-up. This trial is registered on ClinicalTrials.gov Identifier as NCT04384770.
Kishan et al. (Wed,) studied this question.