S984
Clinical - Oligometastatic cancer
ESTRO 2026
Sweden. 6 Radiotherapy, University of Pennsylvania, Philadelphia, USA. 7 Radiotherapy, University Hospital of Zurich, Zurich, Switzerland. 8 Radiotherapy, Froedtert & the Medical College of Wisconsin, Wisconsin, USA. 9 Radiotherapy, University Medical Center Utrecht, Utrecht, Netherlands. 10 Radiotherapy, Sacro Cuore Don Calabria Hospital, Negrar di Valpolicella, Italy. 11 Radiotherapy, Iridium Network, Antwerp, Belgium. 12 Radiotherapy, Institute of Oncology Ljubljana, Ljubljana, Slovenia. 13 Radiotherapy and radiosurgery, IRCCS Humanitas Research Hospital Italy, Milan, Italy. 14 Oncology, University of Turin, Turin, Italy Purpose/Objective: Since the optimal treatment strategy for liver oligometastases remains debated, this study aims to present patient and treatment related factors associated with local control of stereotactic body radiotherapy (SBRT) and their interaction. Material/Methods: Data of liver SBRT patients, treated between April 2019–June 2024, was extracted from two prospective, international registries, MOMENTUM (NCT04075305; MRI-guided [1]) and OligoCare (NCT03818503; mostly CBCT-guided [2]). Inclusion criteria were MRI- or CBCT- guided radiotherapy and, if alive, at least one follow- up moment (up to two years). Exclusion criteria were proton therapy, missing data and registry inclusion <12 months prior. The biologically equivalent planned PTV D98% (BEDD98) was calculated with α / β =1.5Gy (primary tumor origin: prostate), 2.5Gy (breast), or 10Gy (all others). Kaplan-Meier (KM) analyses were performed for local control (LC), with local recurrence defined as recurrence/progression within the PTV. Variables for uni- and multivariable Cox proportional hazards regression analyses were planned BEDD98, image guidance (IG; CBCT/MRI), CTV, primary tumor origin and concurrent systemic therapy. Interaction was assessed between IG and dose and IG and CTV based on KM-curves, split on median dose or median CTV. In case of statistical significance, the interaction was added in the multivariable analyses (MVA), including both BEDD98 and CTV as continuous variables. Significance level α =0.05. Results: A total of 402 patients (499 lesions) were included (Table). Median BEDD98 was 105Gy (IQR 73–173Gy). Median dose and CTV differed between cohorts. For the full cohort, 1- and 2-year LC was 91.9% and 87.9%; 1- and 2-year OS: 81% and 57%.Univariable analyses showed significantly better LC for a BEDD98 above the median (p=0.001), MRI-guidance (p=0.011) and CTV smaller than the median (p=0.0032). A significant interaction for IG and dose was observed, showing significantly better LC for MRI-guidance for BEDD98 ≤ 105Gy (p=0.0017), which was not seen in
characteristics, beam-on time (treatment administration duration), beam-hold time (interruption due to gating), duty cycle (% of beam-on time on the entire duration), positioning shifts. Acute side effects and oncological outcomes were also evaluated. Results: Between September 2023 and October 2025, 40 patients for a total of 44 lesions were treated with liver SBRT at the MR-Linac using CMM. Median dose was 50Gy (range 36-60) in 5 fractions (range 3-10). We used the GTV as “Anatomic Position Monitoring” structure and PTV as “Gating Envelope” and set the VOICE threshold at 95%. All patients completed the treatment. The mean duty cycle for the 212 fractions was 92.83% (95%CI 84.31-95.23%). Mean beam-on time was 12 minutes and 53 seconds (95%CI 9.88- 18.28). Beam-hold occurred in all fractions for a mean count of 59.7 instances (95%CI 43.2-111.9). Fourteen baseline shift plans were performed due to persistent target drifts. We observed 9 cases of CATCAE v5.0 grade (G) 1 fatigue, 6 G1 nausea, 3 G2 nausea, 5 G1 abdominal pain, 2 G1 diarrhea. No ≥ G3 adverse events occurred. With a mean follow up of 8 months (range, 3-24) no ≥ G2 late side effects were recorded, 16 patients had a controlled disease, 9 had a distant progression and/or hepatic out-of-field relapse and 2 an in-field relapses. Conclusion: CMM was efficaciously implemented in our clinical routine in liver SBRT. Treatment duration was only minimally increased and the procedure was well tolerated by all patients. Initial results showed excellent local control with mild adverse events. Keywords: liver metastases, adaptive RT, MR-guided RT Impact of image guidance and dose on local control of patients with liver oligometastases within Momentum and OligoCare studies Julia E Peltenburg 1 , Astrid van der Horst 1 , Rana Bahij 2 , Simon Boeke 3 , Petra M Braam 4 , John P Christodouleas 5,6 , Matthias Guckenberger 7 , William Hall 8 , Martijn PW Intven 9 , Tomas Janssen 1 , Corrie AM Marijnen 1 , Luca Nicosia 10 , Piet Ost 11 , Ivica Ratosa 12 , Marta Scorsetti 13 , Jan-Jakob Sonke 1 , Umberto Ricardi 14 , Helena M Verkooijen 9 , Filippo Alongi 10 , Marlies E Nowee 1 1 Radiotherapy, Netherlands Cancer Institute, Mini-Oral 3779 Amsterdam, Netherlands. 2 Radiotherapy, Odense University Hospital, Odense, Denmark. 3 Radiotherapy, Tuebingen University Hospital, Tuebingen, Netherlands. 4 Radiotherapy, Radboud University Medical Center, Nijmegen, Netherlands. 5 Medical affairs and clinical research, Elekta AB, Stockholm,
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