Purpose: Magnetic resonance-guided stereotactic body radiation therapy (MRgSBRT) has shown promise in delivering ablative doses to liver tumors. We reported the outcomes of patients with unresectable primary liver cancer treated with MRgSBRT with online adaptive planning when indicated.
Methods: Patients with unresectable hepatocellular carcinoma (HCC), cholangiocarcinoma (CCA), and combined biphenotypic hepatocellular-cholangiocarcinoma (cHCC-CCA) who completed MRgSBRT to 50 Gy in 5 fractions between June of 2015 and December of 2021 were analyzed. The distance of the organs-at-risk (OARs) to the Planning Target Volume (PTV) on the simulation scan was assessed using symmetric volumetric expansion of the PTV in 0.5 cm to 2.0 cm in 0.5 cm increments.
Results: Ninety-nine analyzable patients completed MRgSBRT during the study period and 54% had PTVs within 1 cm of the duodenum, small bowel, or stomach at the time of simulation. Online adaptive RT was used in 53% of patients to OAR constraint violation and/or to improve target coverage. PTVs within 1 cm of the duodenum, small bowel, or stomach were significant predictors of online adaptation use with a sensitivity of 88% (95% CI: 77–96%) and a specificity of 85% (95% CI: 72–94%). In patients who underwent adaptive RT planning, online replanning resulted in superior target coverage when compared to projected, non-adaptive plans (median coverage ≥ 95% at 47.5 Gy: 91% [IQR: 82–96] before adaptation vs. 95% [IQR: 87–99] after adaptation, p < 0.01). The 2-year cumulative incidence of local progression was 9.8% (95% CI: 1.5–18%) for patients with HCC and 9.0% (95% CI: 0.1–18) for patients with CCA/cHCC-CCA.
Conclusion: MRgSBRT, with the option for online adaptive planning when merited, allows delivery of ablative doses to primary liver tumors with excellent local control.
Radiation Dosimetry, MRI, Image-guided Therapy
IM/TH- MRI in Radiation Therapy: MRI/Linear accelerator combined (general)