ESTRO 2025 - Abstract Book

S1765

Clinical – Upper GI

ESTRO 2025

1219

Mini-Oral Determining the maximum tolerated dose of MR-guided radiotherapy for (peri)pancreatic tumors (RadioPanc): a phase I dose escalation trial Hidde Eijkelenkamp 1 , Guus Grimbergen 1 , Louk M.W. Snoeren 1 , Jacobien C.M. Scheepens 1 , Lois A. Daamen 1 , Hanne D. Heerkens 2 , Martijn P.W. Intven 1 , Gert J. Meijer 1 1 Department of Radiation Oncology, University Medical Center, Utrecht, Netherlands. 2 Department of Radiation Oncology, Radboudumc, Nijmegen, Netherlands Purpose/Objective: MRI-guided radiotherapy (MRgRT) offers the potential to safely escalate radiation doses for pancreatic cancer beyond the capabilities of conventional radiotherapy. These higher doses could therefore improve local tumor control and enhance the quality of life for patients. However, it is essential to establish the safety and feasibility of delivering higher radiation doses in the pancreatic area within a prospective dose-escalation trial. Therefore, this study aimed to determine the maximum tolerated dose of MRgRT in patients with (peri)pancreatic tumors. Material/Methods: The RadioPanc study was a single center, single arm, phase I dose-escalation trial using a rolling-six design. Patients with (peri)pancreatic tumors were asked to participate in the study. Three dose-escalation levels were established: 40 Gy, 50 Gy, and 60 Gy delivered in five fractions with a 1.5 T MR-linac (Elekta AB, Sweden). The primary endpoint was dose-limiting toxicity (DLT), defined as radiotherapy-related toxicity of grade ≥4 within twelve weeks after MRgRT. The maximum tolerated dose (MTD) was defined as the highest dose level with a DLT rate of ≤17%. Symptoms (abdominal pain, bloating, constipation, diarrhea, gastroparesis, nausea, vomiting, fatigue, and anorexia) were graded with the CTCAE v5. Technical feasibility was assessed by analyzing the GTV V100%, PTV (GTV + 3 mm) V95%, and dose-volume histograms (DVH). Results: All dose levels were fully enrolled and declared safe after no observed DLT. No radiotherapy-related grade 3 toxicities were reported at any dose level. Patient 6 and 18 died during follow-up due to distant disease progression without DLT. Online treatment maps of example cases from each dose level are shown in Figure 1. The median (IQR) GTV V100% and PTV V95% were for dose-level 1: 93% (8%), 85% (11%); level 2: 91% (14%), 83% (16%), and level 3: 82% (27%), 71% (17%). Median DVHs per dose level are shown in Figure 2.