Initial clinical experience with using a 1.5 Tesla MR-Linac for stereotactic body radiotherapy for cancer of the upper abdomen

Background: Traditional radiation therapy for upper abdominal tumors requires relatively large margins around the tumor to account for respiratory motion, which limits the dose that can be safely delivered to the tumor. Magnetic resonance (MR) -guided radiotherapy provides optimal visualization of soft tissues, which can be improved still further by use of contrast-enhancing agents. We describe our preliminary experience with using a 1.5 T MR-linear accelerator (MR-LINAC) device in combination with liver-specific contrast agents for treating patients with upper abdominal tumors. Methods Nine patients with upper abdominal tumors were selected for treatment with stereotactic body radiotherapy under MR guidance; all patients were given a contrast-enhancer before radiotherapy. We also used the same treatment planning system (Monaco, Elekta version 5.40.02) to provide parallel plans for intensity-modulated radiation therapy (IMRT) for each patient, and all treatment plans were reviewed by two experienced radiation oncologists. Results The 9 patients (8 men, 1 woman; median age 64 years) had multiple types of upper abdominal tumors. The radiation dose (e.g., 40 Gy in 5 fractions, 50 Gy in 10 fractions) depended on the tumor location and clinical characteristics. MR imaging provided excellent soft tissue contrast, which was improved further by the injection of enhancing agent, which led to a contrast-to-noise ratio of 19.28 with vs 5.165 without ( P  < 0.05). Conclusion MR-LINAC-based radiotherapy combined with contrast agents allowed abdominal tumors to be located precisely, potentially allowing the use of narrow treatment margins and hence less potential irradiation of normal tissues around the target area.