Skip to main content
ASTRO 2024 Main banner
Icon Legend
Presentation Icons
Event Add-on
Event Add-on
In Person Only
In Person Only
Off-site Event
Off-site Event
Location: Marriott Marquis
Location: Marriott Marquis
Back
Main Session View Poster

PQA 02 - PQA 02 Physics Poster Q&A

2331 - Effect of Prolonged Supine Positioning on CBCT Bowel Gas Artifact in Pancreatic Cancer Patients Undergoing CT-Guided Adaptive Stereotactic Body Radiotherapy

Sunday, September 29, 2024
4:45 PM – 6:00 PM ET
Location: Hall C

Screen: 3

    Presenter(s)

  • Minji Kwon

    Saint Louis University
    St. Louis, MO

K. Kiser1, E. Laugeman1, R. Beckert1, M. Kwon2, A. Mo1, E. Morris1, G. D. Hugo1, C. G. Robinson1, P. Samson1, and H. Kim3; 1Department of Radiation Oncology, Washington University School of Medicine in St. Louis, St. Louis, MO, 2Saint Louis University, St. Louis, MO, 3Department of Radiation Oncology, Washington University School of Medicine, Saint Louis, MO

Purpose/Objective(s): Cone beam computed tomography (CBCT)-based online adaptive stereotactic body radiotherapy can deliver ablative doses to pancreatic cancer. However, bowel gas artifact can degrade the CBCT image used to recontour and replan each adapted fraction. We hypothesized that increased patient time in a pre-treatment supine position would decrease bowel gas artifact. Materials/

Methods: Three radiation oncologists, one medical physicist, and one radiation therapist jointly scored bowel gas artifact in online adaptive CBCTs from pancreatic cancer patients treated with SBRT. Scores were assigned at the level of CBCT images as follows: 1) no gas artifact in the image; 2) no gas artifact within a 3 cm ring expansion surrounding the GTV, or mild artifact within the contour ring with no impact on delineation of organs at risk (OARs); 3) moderate gas artifact within the contour ring but only minimal impact on delineation of OARs; 4) gas artifact significantly obscuring delineation of an OAR within the contour ring. For each fraction, images were equally paired between initial CBCTs (before adaptive planning) and verification CBCTs (before beam-on). Patients with metallic implants, including stents, were excluded. Non-parametric statistical tests were performed using Python libraries.
Results: A total of 1124 CBCT images from 72 CBCTs acquired in 32 adaptive fractions delivered to 18 patients were scored. The median inter-CBCT time (time between initial and verification CBCTs during which patients were supine and motionless) was 35 minutes (interquartile range (IQR) 27.8 – 42.5). Image quality scores (due to gas artifact) were significantly better in verification CBCTs than initial CBCTs (p < 0.001). Verification CBCTs acquired at least 40 minutes after initial CBCTs were associated with improved gas artifact compared to verification CBCTs acquired sooner than 40 minutes (p = 0.05).
Conclusion: In pancreatic cancer patients treated with CBCT-guided adaptive radiation, bowel gas artifact was significantly reduced in verification CBCT images compared to initial CBCT images. Patients presenting with CBCT bowel gas artifact may benefit from prolonged supine positioning on a stretcher or treatment table prior to RT. This study was approved by an institutional IRB (#202312054).