KEY POINTS
- This secondary analysis used data from the randomized phase III MIRAGE trial and included 117 patients with complete baseline and 24-month sexual-function assessments: 58 treated with CT-guided SBRT and 59 with MRI-guided SBRT.
- Both groups received 40 Gy in 5 fractions. CT guidance used a 4-mm CTV-to-PTV margin, while MRI guidance enabled a 2-mm margin with real-time motion management and gating.
- MRI-guided treatment reduced mean bilateral neurovascular bundle V20Gy from 10.8 to 7.3 cc (p<0.0001) and internal pudendal artery V20Gy from 1.3 to 0.3 cc (p<0.05). Bilateral neurovascular bundle V36Gy was also lower at 5.6 versus 8.0 cc.
- Right neurovascular bundle maximum-dose metrics were nominally associated with clinically significant EPIC26 sexual-function decline, but the association was no longer significant after correction for multiple comparisons. No significant associations were identified for SHIM decline.
- Baseline SHIM scores were higher in the MRI arm (17 vs 10.5; p=0.032), and the analysis was exploratory, underpowered, and based on planned rather than delivered dosimetry.
CLINICAL TAKEAWAY
Reduced treatment margins with MRI-guided prostate SBRT may incidentally lower low- and intermediate-dose exposure to the neurovascular bundles and internal pudendal arteries, potentially contributing to the lower sexual-function decline previously reported in MIRAGE. These findings remain hypothesis-generating and should not yet be used to define prospective planning constraints.