ESTRO 2021 Abstract Book

S310

ESTRO 2021

Results Since February 2014 to December 2020, 80 patients (p), 34 male(42.5%) and 46 women(57.5%) were evaluated. Median age: 68 years(35-87). Tumor resectability groups at diagnosis were: resectable 20p(25%), borderline- resectable 32p(40%) and initially unresectable 28p(35%). Induction chemotherapy(CT): 57p(71.3%) nab- paclitaxel+gemcitabine, 14p(17.5%) mFOLFIRINOX, 2p(2.5%), 5FU-based-CT, 1p(1.3%) NALIRINOX, 6p(7.55%), no induction or unknown-CT. CTV was macroscopic tumour, pathological lymph nodes, and perivascular tissue if involved. PTV was CTV+5mm margin. Prescription dose to PTV and fractionation was adapted to tumor volume and constraints to organs at risk: 50Gy(5x10Gy) in 49p(61.3%), 62Gy(10x6.2Gy) in 8p(10%), 60Gy(10x6Gy) in 10p(12.5%), 50Gy(10x5Gy) in 12p(15%) and 40Gy(10x4Gy) in 1p(1.2%). BED 10Gy was ≥90Gy in 67p(83.7%). IMRT/VMAT and daily IGRT was mandatory. Intrafraction control of pancreas motion was performed with respiratory control (ExacTrac-Adaptive-Gating or Active-Breathing- Coordinator systems). After NA, 56p(72.5%) underwent surgery, 19 out of 28 were initially unresectable (67.9%). R0 resection was achieved in 53p(94.6%) and pN0 status in 39p(48.8%) . Tumor regression grade(TRG) was: complete-or-marked response(TRG 0–1) in 26p(46.4%), moderate-response(TRG 2) in 24p(42.6%) and poor-response(TRG 3) in 6p(10.7%). Patients with TRG 0-1 had a better OS (for TRG 2-3 was 22.2months (m), while for TRG 0-1 was not achieved). Median follow-up was 17.4m (3.0 –78.2m) since diagnosis. Actuarial median OS: 22.9m. Actuarial OS at 12, 24 and 36m was 72.8%, 47.6% and 38.9% respectively. Cancer-specific OS was higher for surgical patients (p=0.001). Local progression free survival (L-PFS) was 97.4% at 12m and 86.2% at 24m. Median L-PFS was not achieved. For any kind of progression, the actuarial median PFS was 17.9m. At the time of the analysis 22p are still alive without disease. No grade ≥3 toxicity related to SBRT was observed.

Conclusion Pancreatic SBRT is a feasible and well-tolerated treatment. Into a NA strategy, can improve tumour regression, R0 resections and local control rates . The benefit on OS will be evaluated with longer follow up.

OC-0415 Long-term outcomes of MR-guided SABR & on-table adaptive replanning for unresectable pancreas cancer M. Chuong 1 , K. Mittauer 1 , R. Herrera 1 , T. Romaguera 2 , D. Alvarez 1 , R. Kotecha 1 , M. Hall 1 , A. Kaiser 1 , J. Bryant 3 , J. McCulloch 1 , A. Ucar 4 , F. De Zarraga 4 , S. Aparo 4 , H. Asbun 5 , R. Jimenez 5 , G. Narayanan 6 , S. Joseph 4 , A. Gutierrez 1 , M. Rubens 7 1 Miami Cancer Institute, Radiation Oncology, Miami, USA; 2 Miami Cancer institute, Radiation Oncology, Miami, USA; 3 Moffitt Cancer Center, Radiation Oncology, Tampa, USA; 4 Miami Cancer Institute, Medical Oncology, Miami, USA; 5 Miami Cancer Institute, Surgical Oncology, Miami, USA; 6 Miami Cancer Institute, Interventional Oncology, Miami, USA; 7 Miami Cancer Institute, Office of Clinical Research, Miami, USA