Main Session
Sep
28
PQA 04 - Breast Cancer, Patient Reported Outcomes/QoL/Survivorship, Functional Radiation Medicine, Hematologic Malignancies, Palliative Care, and International/Global Oncology
2872 - Clinical Outcomes and Dose-Response of MR-Linac-Guided SBRT for Colorectal Cancer Liver Metastases: A Real-World Study
Presenter(s)
Yuan Tang, MD - Cancer Hospital, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing, Beijing
J. Shuai1, T. Xu1, N. Wang1, H. Li1, S. Qin1, J. Chen1, Y. Cao1, K. Men1, J. Jin1,2, and Y. Tang1; 1State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences (CAMS) and Peking Union Medical College (PUMC), Beijing, China, 2Department of Radiation Oncology,National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital,Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, China
Purpose/Objective(s):
Magnetic resonance-guided stereotactic body radiotherapy (MR-guided SBRT) using a 1.5T MR-linear accelerator (MR-Linac) enables high-fidelity soft-tissue visualization and online adaptive replanning, which may optimize target coverage and reduce exprosure to organ-at-risk in patients with colorectal cancer liver metastases (CRLM). This study evaluates real-world clinical outcomes, toxicity, and dose-response relationships in patients with CRLM treated with MR-Linac–guided SBRT.Materials/Methods:
We retrospectively reviewed consecutive patients with CRLM treated with 1.5T MR-Linac–guided SBRT between January 2020 and June 2025 at a single institution. All treatments incorporated daily MR guidance with online adaptive planning using an adapt-to-position (ATP) workflow. Intrafraction motion was monitored with real-time cine MRI during abdominal compression. Endpoints included intrahepatic local control (LC), progression-free survival (PFS), overall survival (OS), and treatment-related toxicities graded per CTCAE v5.0. LC and survival estimates were generated using Kaplan-Meier method.Results:
A total of 35 patients with 41 liver metastases were included, with a median follow-up of 10.8 months. Extrahepatic disease was 37% (lung 31%). 91% of patients received SBRT to all liver metastases. Median treated liver metastases was 1 (range 1–3). Most patients had received prior systemic therapy; 57% had one line and 40% had =2 lines. The most common dose-fractionation regimens were 60 Gy in 5 fractions (37%) and 50 Gy in 5 fractions (23%), followed by 60 Gy in 10 fractions (20%) and 50 Gy in 10 fractions (9%). Median biologically effective dose (BED10) was 100 Gy (range, 37.5–132), with 80% of lesions receiving BED10 =90 Gy, and 60% received =100 Gy. All patients completed the planned SBRT, and no grade =3 treatment-related adverse events were observed. The 1- and 2-year LC rates were 73.7% and 65.5%, respectively; median LC was not reached. Median PFS and OS were 8.9 and 33.9 months, respectively. The 1- and 2-year OS rates were 90.4% and 55.1%, and corresponding PFS rates were 33.4% and 23.4%. At first post-treatment imaging, best responses included complete response (2.9%), partial response (42.9%), stable disease (51.4%), and progressive disease (2.9%); the majority of lesions with initial stable disease achieved durable in-field control. On univariate analysis, BED10=90 Gy was significantly associated with improved PFS (HR 0.26, P=0.004) and OS (HR 0.20, P=0.006).Conclusion:
MR-Linac–guided SBRT is feasible and well tolerated, in patients with CRLM achieving favorable intrahepatic local control with minimal high-grade toxicity. A BED10 threshold of =90 Gy may represent a clinically meaningful dose level associated with improved survival outcomes, warranting prospective validation in larger cohorts.