2131 - Risk-Adapted Target Volume Design in FBCT-Guided Adaptive Stereotactic Radiotherapy for Pancreatic Cancer:Clinical Safety, Dosimetric and Spatial Analysis

03:00pm - 04:00pm ET

Poster Hall - Exhibit Hall A

Screen: 31

Presenter(s)

Shuyan Li, PhD - Department of Radiation Oncology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, Shanghai

S. Li¹, W. Qi¹, X. Wu², Y. Wang², F. Wang¹, L. Yao¹, M. Wang¹, and S. Zhao¹; ¹Department of Radiation Oncology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China, ²Shanghai United Imaging Healthcare Co. Ltd., Shanghai, China

Purpose/Objective(s):

Pancreatic SBRT is clinically constrained by radiosensitive gastrointestinal (GI) organs and significant inter-fraction anatomical shifts. This study evaluates fan-beam CT (FBCT)-guided adaptive radiotherapy (ART) using a precision risk-adapted target volume design to enable safe dose escalation while minimizing dose to the stomach and duodenum.

Materials/Methods:

Twelve patients with pancreatic cancer (primary, postoperative recurrent, or oligometastatic) with tumors located in the pancreatic head or nearby regions were analyzed. All received FBCT-guided SBRT (35Gy/5Fx). A risk-adapted strategy was implemented: 1) GTV_40Gy: tumor core with a 0.5 mm safety buffer away from OARs; 2) PTV_35Gy: target excluding a 0.2 mm avoidance zone around OARs; 3) PTV_27Gy: 5mm isotropic expansion from GTV. Daily ART plans were compared to IGRT plans using the Wilcoxon signed-rank test (P<0.05). Target D_95%, D_mean, D_max and OAR D_max, V_20Gy were analyzed. Spatial analysis included centroid displacement and Dice Similarity Coefficients (DSC). Acute toxicities were assessed via CTCAE v5.0.

Results:

FBCT-guided ART demonstrated significant dosimetric advantages. For target, ART improved coverage and reduced deviation: D_95% for GTV_40Gy was 39.9±0.7Gy vs. 36.9±5.7Gy (P<0.001), PTV_35Gy was 34.9±0.9Gy vs. 30.1±7.0Gy (P<0.001), and PTV_27Gy was 31.5±3.0Gy vs. 28.6±7.2Gy (P<0.001). Regarding OAR sparing, ART significantly reduced D_max and volumetric doses; duodenal V_20Gy was 3.23±4.14cc (ART) vs 4.31±5.9cc (IGRT, P<0.001), with similar reductions in stomach, small intestine, and colon D_max. Regarding safety, 4 patients experienced Grade 1 acute toxicity, including nausea (n=4) and vomiting (n=2); no Grade=2 toxicities were observed. Spatial analysis revealed the cephalocaudal (CC) as the dominant displacement axis, with average CC shifts of 9.8±38.3mm (stomach) and 7.9±22.1mm (duodenum). Mean 3D vector displacement reached 28.7±32.4 mm (stomach) and 20.2±18.8mm (duodenum). Low mean DSCs (0.62 for stomach, 0.53 for duodenum) quantified substantial inter-fraction deformation.

Conclusion:

For complex pancreatic and peripancreatic lesions, risk-adapted ART successfully navigates the narrow therapeutic window. By utilizing precision avoidance buffers (0.2mm for PTV_35Gy and 0.5mm for GTV_40Gy), this approach ensures robust dose escalation while addressing substantial CC-dominant spatial variations. The favorable acute toxicity profile and improved dosimetry support FBCT-guided ART as a safe, effective strategy for maximizing therapeutic intensity in pancreatic SBRT.