Stereotactic body radiotherapy (SBRT) has become a standard treatment for localised prostate cancer due to its ability to deliver highly focused radiation while minimising exposure to surrounding healthy tissue. A key element of SBRT is the use of imaging guidance to optimise treatment delivery. The MIRAGE trial highlighted the potential benefits of MRI-guided SBRT in improving treatment outcomes compared to traditional CT-guided methods.
The trial demonstrated that reducing planning margins from the typical 4 mm (using CT guidance) to 2 mm (using MRI guidance) significantly reduced acute grade ≥2 genitourinary (GU) and gastrointestinal (GI) toxicities. However, it was uncertain whether these benefits would persist over longer-term follow-up. In a secondary analysis of this phase 3 trial, researchers assessed physician-scored toxicity and patient-reported quality-of-life (QOL) outcomes at the 2-year mark, a key time point for intermediate follow-up.
Results showed that MRI-guided SBRT led to lower rates of late grade ≥2 GU toxicity (27% vs. 51%; p=0.004) and GI toxicity (1.4% vs. 9.5%; p=0.025) compared to CT-guided SBRT. These findings were sustained over the 2-year follow-up period, suggesting that the initial improvements in toxicity and QOL with MRI guidance were maintained. Logistic regression analysis revealed that patients receiving MRI-guided SBRT had significantly lower odds of experiencing clinically relevant deterioration in bowel function and sexual health scores, indicating sustained benefits in these areas.
Despite these promising results, some discrepancies were noted in urinary toxicity outcomes. These may be linked to the use of α-adrenergic antagonists, which were prescribed to manage urinary symptoms, thus limiting patient-reported QOL deterioration while still registering physician-scored grade 2 GU toxicity. Additionally, while MRI guidance appeared beneficial for erectile function, other aspects of sexual function may not have shown significant improvement due to inherent radiation effects on the prostate and surrounding structures.
Although the trial was not designed to evaluate cost-effectiveness, the findings support the clinical benefits of MRI-guided SBRT, particularly in reducing late toxicity and improving QOL measures such as bowel function and sexual health. Further research is needed to explore long-term outcomes beyond 2 years and to address the financial and practical implications of adopting MRI-guided systems.
In conclusion, MRI-guided SBRT offers a promising approach to reducing long-term toxicity and enhancing QOL outcomes in prostate cancer patients, highlighting the importance of imaging guidance in modern radiotherapy practices.
Katie Wright, EMJ
Reference
Kishan AU et al. Magnetic resonance imaging versus computed tomography guidance for stereotactic body radiotherapy in prostate cancer: 2-year outcomes from the MIRAGE randomized clinical trial. Eur Urol. 2024;DOI:10.1016/j.eururo.2024.10.026.
