3555 - MR-Guided Adaptive Stereotactic Ablative Radiotherapy for Postoperative Recurrent and Metastatic Pancreatic Cancer: Early Efficacy and Toxicity Outcomes

02:30pm - 03:45pm PT

Hall F

Screen: 20

Presenter(s)

Chen Wang, MD - Department of Radiation Oncology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing,

C. Wang¹, F. Zhang², and X. Lian³; ¹Department of Radiation Oncology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China, ²Department of Radiation Oncology, State Key Laboratory of Complex Severe and Rare Diseases, Peking Union Medical College Hospital, Chinese Academy of Medical Science and Peking Union Medical College, Beijing, China, ³Department of Radiation Oncology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, Beijing, China

Purpose/Objective(s):

In patients with metastatic or postoperatively recurrent pancreatic cancer, radiotherapy serves to alleviate symptoms and improve local control, with the potential to prolong survival. Stereotactic ablative radiotherapy (SABR) with a biological effective dose (BED)10 >70 Gy has demonstrated excellent local control and potential overall survival benefits in locally advanced pancreatic cancer. When combined with online adaptive radiotherapy, SABR achieves precise dose delivery while minimizing adverse effects. However, its feasibility in metastatic or recurrent disease remains uncertain.

Materials/Methods:

A single-institution retrospective analysis was conducted on patients with metastatic or postoperative recurrent pancreatic cancer who underwent ablative stereotactic MR-guided on-table adaptive radiation therapy using a 1.5T MR-Linac from August 2023 to August 2024. The clinical target volume (CTV) for SABR included gross disease and the full circumference of involved vasculature at the level of tumor involvement. The planning target volume (PTV) was generated by expanding the CTV by 3 mm. Pain was assessed using the Brief Pain Inventory (BPI) scale, and quality of life was evaluated using the EORTC Questionnaire-C15-PAL.

Results:

A total of 14 patients with metastatic or postoperatively recurrent pancreatic cancer underwent SABR targeting the pancreatic lesions, including 5 with postoperative recurrence and 9 with metastatic disease (liver: 2; retroperitoneum: 1; bone: 1; lung: 1; multiple metastases: 4). All patients received prior chemotherapy, most commonly the AG regimen (gemcitabine + nab-paclitaxel, n=9, 64%). SABR was delivered at 40-50 Gy in 5-7 fractions (BED10 = 72-100 Gy) using abdominal compression with a pressure plate to restrict organ motion. At a median follow-up of 6 months (range: 3-11 months), 79%(n=11) achieved local control, 14%(n=2) of local progression. One patient with metastatic disease died 3 months after treatment. Three postoperative recurrence patients developing liver metastases. Only 1 patient experienced grade 1 diarrhea, with no grade =2 adverse events. All patients reported pain reduction or complete resolution. Quality of life was maintained or improved compared to baseline.

Conclusion:

This study is the first to demonstrate that MR-guided adaptive radiotherapy (MRgART) for stereotactic ablative radiotherapy (SABR) targeting pancreatic lesions in patients with metastatic or postoperatively recurrent pancreatic cancer achieves excellent local control rates and favorable safety profiles, effectively alleviates pain, and maintains quality of life. Currently, our institution employs 50 Gy in 5 fractions as the standard radiotherapy regimen in cases where there are no organs at risk constraints. Further data collection and extended follow-up are required to validate these findings and establish the optimal treatment regimen.