KEY POINTS
- This single-institution retrospective analysis included 20 patients with well-differentiated G1–G3 gastroenteropancreatic neuroendocrine tumors treated with MR-guided RT between 2019 and 2023; 90% had metastatic disease at treatment.
- Treatment was delivered on an MR-guided linear accelerator using daily adaptive planning, breath-hold, and real-time target tracking. Fractionation ranged from 5–10 fractions, most commonly 12 Gy ×5 (35%) and 10 Gy ×5 (25%).
- The median delivered biologically effective dose was BED10 100 Gy (IQR 83.3–132), with a median GTV of 20.5 cm³ and PTV of 25.6 cm³.
- Only one in-field failure occurred, 16 months after treatment of an upper abdominal lymph node. Crude local control was 95%, with estimated 3-year local control of 94% (95% CI 83–100%); no marginal failures were identified.
- Among pancreatic targets, local control was 100%, an important technical signal given the proximity of radiosensitive bowel and difficulty of delivering ablative dose safely in this region.
- Twelve patients developed distant progression. Median progression-free survival was 30 months (95% CI 16–not reached), with PFS of 74% at one year, 57% at two years, and 45% at three years.
- Treatment-related toxicity occurred in 5/20 patients (25%). Two patients (10%) experienced acute grade 3 toxicity involving abdominal pain and/or nausea; no late treatment-related toxicity and no grade 4–5 events were observed.
CLINICAL TAKEAWAY
Ablative MR-guided RT appears capable of durable local control for selected GEP-NET lesions, including pancreatic targets, and may be attractive when surgery or other locoregional therapies are unsuitable. The 95% control rate is compelling but comes from only 20 heterogeneous patients without a comparator, so it should be viewed as a strong feasibility signal rather than definitive efficacy evidence.