2107 - Fan Beam Computed Tomography-Guided Adaptive Radiotherapy (FBCT-gART) Combined with Four-Dimensional Computed Tomography (4DCT) of Pancreatic Cancer: A New Workflow and Dosimetric Benefits

02:30pm - 04:00pm PT

Hall F

Screen: 26

Presenter(s)

Wenjing Huo, RT - Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, Shandong

W. Huo¹, L. Xu¹, S. He², and J. Yue¹; ¹Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China, ²United Imaging Research Institute of Intelligent Imaging, Beijing, China

Purpose/Objective(s):

This study aimed to develop the workflow integrating fan-beam computed tomography-guided adaptive radiotherapy (FBCT-gART), four-dimensional computed tomography (4DCT), and abdominal compression (AC) for locally advanced pancreatic cancer(LAPC), focusing on its feasibility and potential benefits.

Materials/Methods:

Four patients with LAPC receiving 60 Gy in 15 fractions using FBCT-gART with 4DCT were analyzed.

The online adaptive workflow included: (1) Acquisition of 4DCT under AC; (2) Automated contours of organs at risk (OARs) and gross tumor volume (GTV) are transferred between the previous and current FBCT scans using deformable registration, followed by manual refinement to ensure accuracy;(3) The internal gross tumor volume (IGTV) is generated using phase-specific GTV modifications (0%, 30%, 50%) and verified to ensure adequate target coverage during respiratory motion. The clinical target volume (CTV) and planning target volume (PTV) are delineated using institutional margin protocols. OAR dose limits are strictly adhered to, with target coverage compromised if necessary.

During treatment, three sets of 4DCT scans were obtained for each of the first three fractions, including 4DCT-1 (post-positioning), 4DCT-2 (pre-beam-out), and 4DCT-3 (post-beam-out). In subsequent fractions, three sets of 4DCT scans were obtained weekly, and for the remaining fractions, only one set of 4DCT was acquired, specifically post-positioning. 4DCT-2 is utilized to verify the tumor location following the adaptive processing time.

Workflow efficiency was evaluated by analyzing treatment duration and the dice similarity coefficient (DSC) of the internal gross tumor volume (IGTV).

Dosimetric benefits were evaluated using paired t-tests to compare target coverage and OAR doses between non-adaptive radiotherapy (nART) and adaptive radiotherapy (ART) plans.

Results:

A total of 117 4DCT scans were acquired, with a median workflow time of 34.35 minutes(range,23–60). Median DSC for IGTV were 0.91 (4DCT1-4DCT2) and 0.90 (4DCT2-4DCT3).

All treatment fractions achieved clinically acceptable plans without treatment discontinuations due to intolerance. Compared to the nART group, ART group demonstrated significantly reduced the maximum dose(Dmax)and the dose received by 2 cm³(D2 cc)for the duodenum and stomach (all p < 0.05) while improving PTV D95% (ART 43.66±4.54, nART 37.08±8.16,p < 0.001).

Conclusion:

This study introduces a clinically feasible workflow integrating 4DCT with FBCT-gART for LAPC patients, offering an innovative solution to mitigate tumor motion challenges. The workflow also demonstrates significant reductions in OAR doses. However, these findings require further validation in larger patient cohorts.