KEY POINTS
- Retrospective single-center analysis of 31 male patients with pelvic lymph node metastases treated using a “Virtual MR-Linac” workflow between November 2023 and January 2025.
- The workflow used daily treatment-position 1.5 T magnetic resonance imaging, synthetic computed tomography from T1 DIXON sequences for dose calculation, adaptive contouring on 2-dimensional T2 turbo-spin-echo images, and treatment delivery on a C-arm linear accelerator with cone-beam computed tomography positioning.
- Across 99 adapted fractions, treatment was completed as planned in all cases; 52% of patients received 10 Gy in 2 fractions, and 35% received 35 Gy in 5 fractions.
- Plan adaptation produced a median 14% increase in planning target volume coverage and a 7% reduction in bowel D1cc.
- Median total session time was 104 minutes; median imaging, contouring, and planning times were 12, 12, and 20 minutes, respectively. Independent Monte Carlo quality assurance showed a median gamma passing rate of 99.7%.
CLINICAL TAKEAWAY
This study shows that magnetic resonance-informed online adaptation can be implemented without an integrated magnetic resonance linear accelerator by decoupling diagnostic-quality magnetic resonance imaging from cone-beam computed tomography-based delivery. The dosimetric signal is useful, especially for pelvic nodal targets affected by bowel and bladder variability. But this remains technical implementation evidence: single center, small cohort, long session times, no real-time beam-on magnetic resonance imaging, and no clinical outcome or toxicity validation.