Research Article|Articles in Press, 100488

MR-Guided SBRT/Hypofractionated RT for Metastatic and Primary Central and Ultracentral Lung Lesions

Open AccessPublished:February 24, 2023DOI:
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      The recent results from Nordic-HILUS study indicate SBRT is associated with high-grade toxicity for ultracentral (UC) tumors. We hypothesized that Magnetic Resonance-guided Stereotactic body radiation (MRgSBRT) or hypofractionated RT (MRgHRT) enables safe delivery of high dose radiation to central and UC lung lesions.


      Patients with UC or central lesions were treated with MRgSBRT/MRgHRT with real-time gating or adaptation. Central lesions were defined as per the RTOG and UC as per the HILUS definitions: Group A tumors < 1 cm from the trachea and/or mainstem bronchi or Group B < 1 cm from lobar bronchi. Kaplan-Meier estimate and log rank test were used to estimate survival. Associations between toxicities and other patient factors were tested using Mann Whitney U test and Fisher’s exact test.


      47 patients were included with median follow-up of 22.9 months (95% CI 16.4 – 29.4). A majority (53%) had metastatic disease. All patients had central lesions and 55.3% (n=26) had UC Group A. Median distance from the proximal bronchial tree was 6.0 mm (range 0.0 – 19.0 mm). Median biologically equivalent dose (α/β=10) was 105 Gy (range 75 - 151.2). The most common radiation schedule was 60 Gy in 8 fractions (40.4%). A majority (55%) had prior systemic therapy, 32% had immunotherapy and 23.4% had previous thoracic RT. Sixteen patients underwent daily adaptation. One-year overall survival was 82% (median not reached), local control 87% (median not reached) and progression free survival 54% (median 15.1 months, 95% CI 5.1 – 25.1). Acute toxicity included Grade 1 (26%) and Grade 2 (21%) with only 2 patients experiencing Grade 3 (4.3%) in the long term. No Grade 4 or 5 toxicities were seen.


      Prior studies noted high rates of toxicity after SBRT to central and UC lung lesions, with reports of Grade 5 toxicities. In our cohort, the use of MRgSBRT/MRgHRT with high BEDs was well tolerated with two Grade 3 toxicities with no Grade 4/5.