ESTRO 2025 - Abstract Book

S1832

Clinical – Upper GI

ESTRO 2025

BED ≥ 100 Gy improve local control; however the optimal “safe” dose remains unknown. We here report the early results of Institutional trial of LAPC patients (pts) receiving 50Gy in 15 frs concomitant to capecitabine.

Material/Methods: Consecutive pts with LAPC still not resectable after induction CHT were considered. All pts underwent simulation contrast-enhanced computed tomography and FDG-PET. CTV was defined as the pancreas site containing the tumor (head, body, tail). PTV1 was defined by adding 1.0 cm in axial and 1.5 cm in cranial-caudal directions to CTV. Primary tumor was defined as GTV. PET positive volumes were merged with GTV and isotropically expanded of 0.5 cm to generate PTV2. Duodenum and stomach were contoured and expanded of 5 mm to create their corresponding PRVs. Dose prescription: 37.5Gy to PTV1, 44.25Gy to overlap between PTV2 and PRVs, 50Gy to remaining PTV2. Constraints derived by our published analysis (2) were for stomach: D 0.03cc<45 Gy, V44 Gy<2cc; for duodenum: D 0.03cc<47Gy, V44 Gy<9cc). Concomitant CHT was capecitabine 1250 mg/day. Results: From May 2021 to June 2024, 27 pts were treated. Median follow-up was 19.91 months. Median number of induction CHT cycles was 6. All pts completed RT-CHT. No pts experienced G≥3 GI acute toxicity, 3 pts had G3 lymphopenia. Two pts were lost and not evaluable for late toxicity and outcome. One patient had local and distant progression 57 days after the end of RT, developed a pseudoaneurysm of the gastroduodenal artery and died the day after its embolization with CT diagnosis of duodenal ischemia. No further late toxicity occurred. Two pts did not received induction CHT and 2 pts were lost, thus 23 pts were considered evaluable for outcome. Twenty-one pts had disease progression, 4 local, 14 distant and 1 local+distant. Two patients had only increase in CA19.9. Thirteen pts died. Median PFS, LPFS and OS, calculated from the start of induction CHT, were 13.87, 35.03 and 24.8 months, respectively. Local control at 1 and 2 years was 87% (SE±7%) and 65% (SE±10%).

Conclusion: The present schedule of hypofractionated RT is feasible with acceptable toxicity rate, provides PFS and OS comparable with standard schedule; local control is encouraging. The study is ongoing.