MR-guided online adaptive stereotactic body radiotherapy (MRgSBRT) of primary lung tumors and lung oligometastases.

Purpose: Stereotactic body radiotherapy is pivotal in the treatment of lung tumors, demonstrating effective local control. However, challenges persist with intra-fractional anatomical changes and organs at risk during delivery. Magnetic resonance-guided online adaptive stereotactic body radiotherapy (MRgSBRT) represents a novel technique promising to achieve safe delivery of ablative doses with improved outcomes for primary lung tumors or lung oligometastases.

Methods: In this single-institution retrospective analysis, we evaluated 64 patients (92 lesions) with primary lung cancer or lung oligometastases treated with MRgSBRT. Using Kaplan-Meier method and log-rank test; we estimated local control (LC), local progression-free survival (LPFS), distant progression-free survival (DPFS), and overall survival (OS).

Results: A total of 64 patients (92 lesions) treated with MRgSBRT were included comprising 14.1% primary lung cancer lesions and 85.9% lung oligometastases. Median total dose, fraction number, fraction dose and BED₁₀ were 50 Gy (range, 21-70 Gy), 5 (range, 1-10), 10 Gy (range, 6-34 Gy), 100 Gy (range, 48-180.0 Gy) respectively. Of the 420 fractions administered, 88.6% (n = 372) involved on-table adapted plans. Median LPFS was not reached and the 1‑ and 3‑year LPFS rates were 96.3% (95% CI 92.4-100.0%) and 86.4% (95% CI 76.9-95.9%), respectively. No local recurrences were observed post-treatment with a total dose of > 50 Gy, BED10 > 100 Gy, fractional dose of > 10 Gy or a CCI > 0.96.

Conclusion: Our study of MRgSBRT in 92 lung lesions revealed a 1-year and 3‑year LPFS rates of 96.3 and 86.4%, respectively without ≥ grade 3 toxicity. Future prospective studies evaluating lung MRgSBRT are awaited.