Oral Presentation The Pancreas Summit 2025

Combined Chemotherapy and Phosphorus-32 Microparticle Intra-Tumoural Implantation Is Better Than Combined Chemotherapy and Stereotactic Body Radiation Therapy for Patients With Locally Advanced Pancreatic Adenocarcinoma (126933)

Amanda Lim 1 2 , Aaron Jin 3 , Pathipat Durongpongkasem 1 , Faisal Ali 4 , Joshua Zobel 1 , Romina Safeian 1 , An Phan 1 , Nimit Singhal 5 , Dylan Bartholomeusz 6 , Hien Le 3 , Nam Nguyen 1 2
  1. Department of Gastroenterology and Hepatology, Royal Adelaide Hospital, Adelaide, SA, Australia
  2. The University of Adelaide, Adelaide, SA, Australia
  3. Department of Radiation Oncology, Royal Adelaide Hospital, Adelaide, SA, Australia
  4. Beth Israel Deaconess Medical Center, Boston, MA, USA
  5. Department of Oncology, Royal Adelaide Hospital, Adelaide, SA, Australia
  6. Department of Nuclear Medicine, Royal Adelaide Hospital, Adelaide, SA, Australia

Background: Although the role of radiotherapy in locally advanced pancreatic cancer (LAPC) is still debated, data has demonstrated encouraging results for more precise methods of radiotherapy delivery, including stereotactic body radiation therapy (SBRT) and endoscopic ultrasound (EUS) guided intra-tumoural phosphorus-32 (32P) microparticle implantation. We compare survival and safety outcomes of patients with SBRT versus EUS-guided 32P implantation in combination with chemotherapy in patients with LAPC.

Method: This is a single-centre retrospective study from March 2015 – April 2025 including all patients with LAPC who underwent combination neoadjuvant chemotherapy with either EUS-guided 32P microparticle implantation or SBRT. The primary outcome was overall survival from chemotherapy commencement. Secondary outcomes include progression-free survival (PFS), resection rate and rate of adverse effects including grade 3 (CTCAE v. 5) or above adverse effects.

Results: A total of 119 patients (58 32P vs. 61 SBRT) were included. Demographics and tumour characteristics were comparable between the groups. All 32P microparticle implantation was successful, with an average volume of 1.6+0.1mL and an estimated 100Gy activity applied to the tumour. The median highest dose of SBRT therapy was 35Gy (IQR 35-40Gy) delivered over 5 fractions. Median overall survival from the date of chemotherapy commencement was significant better with 32P implantation than SBRT (hazard ratio [HR] 1.98; p=0.004). Compared to SBRT, 32P implantation was associated with superior local and distant PFS (HR 1.61; p=0.034 and HR 1.71; p=0.019 respectively). Both therapies resulted in significant reduction in serum Ca19.9. Tumour downstaging (15/58 vs. 5/61, P<0.001) and surgery (13/58 vs. 0/61, P<0.001) rates after the therapy were significant higher with 32P implantation than SBRT. The rate of R0 resection was 77% (10/13) in the 32P group. The rate of grade 3 adverse events was not significantly different between the groups (6/58 vs. 5/61).

Conclusion:  When radiotherapy is used in combined with chemotherapy for LACP, EUS guided intra-tumour 32P implantation is associated with better clinical outcomes than SBRT, including overall and progression free survival, tumour downstaging and surgical resection.  Both forms of radiotherapy have demonstrated a good safety profile. These findings warrant further evaluation with a larger randomized controlled trial.