3567 - LINAC-based Stereotactic Ablative Radiotherapy (SABR) for Pancreatic Cancer: Toxicity Profile and Outcomes
Presenter(s)
Y. R. Wuu1,2, B. Gui1,2, K. Gill1,2, R. Chan1,2, J. L. Karten1,2, B. Khandakar2,3, B. U. Sidiqi1,2, J. M. Herman1,2, D. King2,4, and M. Ghaly1,2; 1Department of Radiation Medicine, Northwell, New Hyde Park, NY, 2Northwell, New Hyde Park, NY, 3Department of Pathology, Northwell, New Hyde Park, NY, 4Department of Medical Oncology/Hematology, Northwell, New Hyde Park, NY
Purpose/Objective(s): With growing evidence supporting ablative radiation therapy (RT) as a promising alternative to standard-dose RT for pancreatic cancer, this study aims to assess the feasibility and safety of LINAC-based Stereotactic Ablative Radiotherapy (SABR) (50 Gy/30 Gy in five biweekly fractions) with real-time fiducial-based respiratory motion tracking.
Materials/Methods: We retrospectively reviewed treatment characteristics and outcomes of pancreatic cancer patients who received SABR (50 Gy/30 Gy in five biweekly fractions) following a median of 8 cycles of 5-fluorouracil or gemcitabine-based chemotherapy in 85% of patients. All patients underwent 4D planning CT with contrast. Radiotherapy was delivered using LINAC-based technology with fiducial-based respiratory motion tracking. Planning target volumes (PTVs) were created: PTV_50 (iGTV + TVI) and PTV_30 (iGTV + TVI + 5mm). Patient data, including demographics, stage, and toxicities profile, were collected under IRB approval. Local control (LC) and overall survival (OS) were assessed using Kaplan-Meier methods with log-rank tests. Dosimetric parameters were compared using t-tests.
Results: 41 patients were included. The median age was 72 years (60% female) with stage II-III disease in 90%. 8 patients were resectable (R), 18 borderline resectable (BR), 11 with unresectable (UR) disease, and 4 metastatic (M) Tumors were located in the pancreatic head (30), body (9), and tail (2). The mean GTV-to-bowel PRV (bowel + 2-3mm) distance was 0.3 cm. Median PTV50 max, min, and mean dose were 5943.7 cGy, 3824.3 cGy, and 5323 cGy, respectively. The median PTV D90 and V90 were 5028 cGy and 95%, respectively. After a mean follow-up of 12.5 months (5–55), 44% (18/41) of patients experienced Grade 1 GI toxicity (N/V/D, pain), six patients had Grade 2 toxicity, and one had Grade 3 toxicity – obstructive cholangitis requiring laparoscopic cholecystectomy. The 2-year LC rates were 100% for R patients, 70% for BR, and 58% for UR patients (p = 0.32). Three patients had isolated local failure. Distant metastases occurred in 41% (17/41) of patients, with five experiencing both local and distant failure, after a median of 4 months. GTV-to-bowel PRV distance <0.3 cm was associated with significantly lower D90 (4720 cGy vs. 5024 cGy, p = 0.01) and V90 (93% vs. 98%, p = 0.01). Dosimetric parameters were not significantly associated with LC (p > 0.2). 2-year OS rates were 43% (R), 21% (BR), 20% (UR), and 0% (M) (p = 0.6).
Conclusion: LINAC-based SABR with fiducial-based respiratory motion tracking provides high-precision radiotherapy for pancreatic cancer, demonstrating feasibility and efficacy in improving local control. Further studies are necessary to evaluate the optimal timing between radiation and chemotherapy to maximize surgical conversion rates and improve overall survival.