3421 - Stereotactic Ablative MR-Guided Online Adaptive Radiation Therapy (SMART) for Management of Borderline Resectable and Locally Advanced Pancreatic Carcinoma
Presenter(s)
N. Dincer1, C. Atahan1, G. Gungor2, T. Zoto Mustafayev3, G. Ugurluer1, M. U. Abacioglu4, B. Atalar1, and E. Ozyar1; 1Department of Radiation Oncology, Acibadem MAA University School of Medicine, Istanbul, Turkey, 2Acibadem MAA University, Maslak Hospital, Radiation Oncology, Istanbul, Turkey, 3Department of Radiation Oncology, Acibadem Maslak Hospital, Istanbul, Turkey, 4Department of Radiation Oncology Acibadem University, School of Medicine. Acibadem Altunizade & Atasehir Hospitals, Istanbul, Turkey
Purpose/Objective(s): The majority of non-metastatic pancreatic cancer patients present at diagnosis with borderline resectable (BRPC) or locally advanced (LAPC) stages unsuitable for surgery. The primary treatment for these patients is chemotherapy and the role of radiotherapy is not yet well established with an increasing trend towards stereotactic body radiotherapy. Stereotactic MR-guided adaptive radiotherapy (SMART) offers advantages such as online adaptive planning in each fraction, enabling dose escalation and protection of organs at risk (OAR). In this study, we aimed to present our outcomes of SMART for BRCP and LAPC.
Materials/Methods: In this IRB approved retrospective study, 53 patients with BRPC or LAPC treated with SMART between September 2018 and October 2024 were analyzed. Treatment was delivered using a 0.35 MR-linac with daily adaptive planning and respiratory gating. Dosimetric parameters, toxicity, and survival outcomes were recorded. Responses were evaluated using PERCIST 1.0 and/or RECIST 1.1 criteria. Local progression free survival (LPFS), distant progression free survival (DPFS), and overall survival (OS) were calculated using the Kaplan-Meier method and log rank test. Toxicity was assessed based on CTCAE v5.0.
Results: The median age was 60.5 (range, 35-90 years), 56.6% of the patients were female and 96.0% had ECOG PS 0-1. Median total dose was 45 Gy (range, 30-50 Gy) and all patients were treated in 5 fractions. Median BED10 was 85.5 Gy (range, 48-100 Gy). In 96.2% of fractions (255/265), adapted plans were used. Twenty-two (36.1%) patients received elective nodal irradiation. Median gross tumor volume was 52.7 cc (range 7.3-133) and median planning target volume was 76.5 cc (range, 13.4-193.4). The median follow-up was 8.3 months (range, 1.2-54.0 months). The median LPFS from the SMART was not reached, 1- and 2-year LPFS from the SMART was 76.3% and 56.5%, respectively. Thirteen patients (21.2%) underwent surgery after SMART, with R0 resection achieved in all but one case. ypT0 rate was 15.4% in resected patients. ypN0 rate was 61.5%. The DPFS from SMART at 1- and 2-year were 38.8% and 20.1%, respectively. The main sites for failure were liver, peritoneum and bone. Median OS from SMART was 31.3 months. Estimated 1- and 2-year OS rates from SMART was 78.2% and 67%, respectively. All patients completed treatment without any acute grade =3 toxicity. Eight patients experienced mild symptoms that resolved within one month, and one patient had postoperative upper gastrointestinal bleeding not attributed to radiotherapy.
Conclusion: SMART for BRPC and LAPC demonstrated high local control rates, promising survival outcomes, and a favorable toxicity profile. These results suggest SMART can be safely and effectively integrated into multimodal treatment approaches for LAPC and BRCP. Further studies with longer follow-up are warranted to confirm these findings.