ESTRO 2023 - Abstract Book

S1100

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ESTRO 2023

Stereotactic ablative radiotherapy has emerged as a promising new treatment modality for patients with pancreatic cancer (PC). With the introduction of online adaptive MR-guided radiotherapy (MRgRT), the treatment has evolved dramatically. It is now possible to define the organs at risk (OAR) and adapt the radiotherapy plan daily based on the anatomy of the day. In this study, we want to investigate the feasibility, efficacy, safety, and overall survival of patients with pancreatic cancer treated with ablative radiation on a 1.5 T MR linac. Materials and Methods The study includes all 52 patients with biopsy-proven PC treated at Odense University Hospital between Aug 2018 and Sept 2022 on a 1.5 T MR Linac. Twenty-five patients were included in the prospective Danish phase II study SBRT-PC-01 (NCT03648632) and 27 patients were included prospectively in The Multiple Outcome Evaluation of Radiation Therapy Using the MR-Linac (MOMENTUM) study (NCT04075305). The prescribed GTV dose was 50 Gy in 5 fx (n=49) or 60 Gy in 8 fx (n=3), with dose constraints to adjacent organs at risk as the limiting factor. Endpoints were adverse events (baseline, 1, 3, 6, 9, and 12 months after RT), and overall survival (OS). Results Of the 52 included patients, 43 were locally advanced, six were locally recurrent, and three were metastatic. The majority of the patients had induction chemotherapy (FOLFIRINOX, Gemcitabine and Nab-paclitaxel, or Gemcitabine and Teysuno (S1)). The median age was 69 years (range 40-85). Fifty participants completed the prescribed radiation treatment. The treatment of the remaining two patients was discontinued after two fractions due to biliary obstruction. Hence, the incompletion of the treatment course was not related to radiation induced adverse events. The median follow-up time from diagnosis and inclusion was 29.5 and 19.8 months, respectively. OS data is presented in the figure. The median OS from diagnosis and inclusion in the study was 27.8 (95% CI 20.8-not reached) and 15.3 months (95% CI 10.2-not reached). Overall, the treatment was well tolerated with no grade ≥ 3 toxicity observed. Nausea and abdominal pain were the main observed adverse events.

Conclusion Online adaptive MRgRT using ablative doses for patients with PC is well tolerated and feasible. It shows promising results regarding survival and efficacy. A prospective trial on this subject is currently being planned.

PO-1371 A simplified method for delineation of target volumes in 4D oesophageal cancer radiotherapy

G. Lewis 1 , O. Nicholas 2 , S. Gwynne 2,5 , T. Crosby 3 , A. Chand 3 , B. Thomas 3 , L. Wills 1 , G. Radhakrishna 4

1 Velindre Cancer Centre, Medical Physics, Cardiff, United Kingdom; 2 South-West Wales Cancer Centre, Clinical Oncology, Swansea, United Kingdom; 3 Velindre Cancer Centre, Clinical Oncology, Cardiff, United Kingdom; 4 The Christie, Clinical Oncology, Manchester, United Kingdom; 5 Swansea University, Medical School, Swansea, United Kingdom Purpose or Objective The guidance for delineation of target volumes for oesophageal cancers being treated using 4DCT within the SCOPE2 trial was updated in an effort to streamline the outlining process. The streamlined method reduces the editing for OARs and ITV creation to a single breathing phase, rather than three. The ITV is then reviewed on all breathing phases to ensure coverage is achieved. This sub-study was designed to investigate whether 4D outlining requirements can be adapted in this way to reduce the demands on clinicians’ time, whilst maintaining robustness in the final target volumes. Materials and Methods Three anonymised 4DCT datasets were distributed to a group of 6 independent observers with experience in outlining target volumes for oesophageal radiotherapy. In each case, the GTV was provided for the reference, maximum inhalation and maximum exhalation breathing phases. Each participant was asked to outline 1 case using both the existing 4DCT delineation guidance published in the SCOPE2 Radiotherapy Planning Guidance Document (RPGD) and the streamlined guidance. Each of the cases were reviewed by an experienced consultant clinical oncologist to determine whether the outlining protocol had been followed correctly. The Jaccard similarity index (JCI) and geometric miss index (GMI) were used to quantify the similarity of the ITV and PTV for both delineation methods.

Results