ESTRO 2022 - Abstract Book

S179

Abstract book

ESTRO 2022

(duodenum V44<9.1cc, D 0.03 <46.7Gy; stomach D 0.03 <45Gy) may help in planning optimization and in implementing future dose escalation trials.

MO-0221 Short-term toxicity outcomes after MR-guided SBRT for (peri-)pancreatic tumors on a 1.5T MR-linac

H. Eijkelenkamp 1 , G. Grimbergen 1 , H. Heerkens 1 , G. Meijer 1 , L. Daamen 1 , Q. Molenaar 2 , H. van Santvoort 2 , B. Erickson 3 , W. Hall 3 , M. Intven 1 1 University Medical Center Utrecht, Department of Radiotherapy, Utrecht, The Netherlands; 2 Regional Academic Cancer Center Utrecht, Department of Surgery, Utrecht, The Netherlands; 3 Medical College of Wisconsin, Department of Radiotherapy, Milwaukee, USA Purpose or Objective Radiotherapy treatment of pancreatic cancer can be challenging due to the close relationship between the tumor and radiosensitive intestines and poor visibility of the upper abdomen with conventional treatment methods. In recent years, with the introduction of MR-guided radiotherapy (MRgRT), it became possible to deliver ablative doses to (peri-)pancreatic tumors. In this multicenter cohort study, we report short-term toxicity from our first cohort of patients with (peri- )pancreatic tumors with MR-guided SBRT on a 1.5 T MR-linac. Materials and Methods All patients with (peri-)pancreatic tumors treated on the 1.5 T Unity MR-linac (Elekta AB, Stockholm, SE) between April 2019 and July 2021 at University Medical Center Utrecht and Medical College of Wisconsin were prospectively included in the Multi-OutcoMe EvaluatioN of radiation Therapy Using the MR-Linac Study (MOMENTUM) (NCT04075305). Toxicity was reported using clinician-reported outcome measurements defined by the Common Terminology Criteria for Adverse Events (CTCAE) version 5. Toxicity was assessed at baseline, and at 3, 6 and 12 months after treatment. Results Baseline data was available for 61 patients with an average follow-up time of 5 months. The median age was 70 years (range 38-91 years) and 35 patients were male (57%). Baseline characteristics are summarized in Table 1. The most frequently delivered SBRT scheme was 40 Gy in 5 fractions of 8 Gy. Most frequently reported toxicities after treatment were fatigue, nausea, anorexia, and diarrhea. The course of these toxicities over time is illustrated in Figure 1. Other grade 3 toxicity at 3 months follow up occurred in 2% of patients for vomiting; 2% for gastroparesis; 4% for malabsorption; 2% for weight loss; 2% for portal hypertension and 2% for gallbladder obstruction. At six months, other grade 3 toxicity occurred in 3% of patients for pancreatitis, and 7% for weight loss. At 12 months 8% had grade 3 weight loss. No treatment-related toxicities higher than grade 3 were observed in our cohort.

Figure 1. Toxicity outcomes