S Han-Oh¹*, L Hsu², C Hill¹, H Lin³, A Martin-Gomez^3,4, A Narang¹, (1) Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University, Baltimore, MD, (2) Office of Capacity Management and Operations Integration, Johns Hopkins Health System, (3) Laboratory for Computer Aided Medical Procedures, Johns Hopkins University Whiting School Of Engineering, MD, (4) Chair for Computer Aided Medical Procedures and Augmented Reality, Department of Informatics, Technical University of Munich, Munich, Germany

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  S Han-Oh

WE-IePD-TRACK 5-7 (Wednesday, 7/28/2021) 5:30 PM - 6:00 PM [Eastern Time (GMT-4)]

Purpose: Deep-inspiration breath-hold (DIBH) is often employed to minimize respiratory-induced tumor motion in pancreatic stereotactic body radiotherapy (SBRT). Spirometer systems such as the Active Breathing Coordinator (ABC) assists patients during the DIBH process to promote reproducibility in tumor position, but how breath-hold parameters and daily variation in bowel gas patterns influence tumor position is unclear. We investigated the impact of these variables on tumor-position reproducibility (BH_Tumor_Var).

Methods: Twenty pancreatic cancer patients who underwent DIBH SBRT were selected for the study. A total of 379 DIBH simulations and CBCT images and the corresponding ABC signals were analyzed. The tumor position was quantified as the centroid of three fiducial makers implanted into the tumor. The BH_Tumor_Var was defined as a relative shift of the centroid compared to that in the planning CT. The ABC signal of each image was characterized based on breath-hold duration (BH_Duration), percentage of inhaled volume relative to the total lung volume (Lung_Utilization), and rate of inhalation (Inhale_Rate). The total lung and gastrointestinal gas volumes (Lung_Volume and GI_Gas_Volume) were also quantified. Multivariate linear regression analysis was performed to understand a correlation between the five variables and BH_Tumor_Var.

Results: The Inhale_Rate was the only statistically significant variable for BH_Tumor_Var in SI. As the Inhale_Rate increased, the tumor moved inferiorly. The BH_Duration, Lung_Utilization, and changes in GI_Gas_Volume were correlated with BH_Tumor_Var in AP. The tumor moved posteriorly when the BH_Duration, Lung_Utilization, and GI_Gas_Volume were shorter, higher, and increased, respectively. The BH_Tumor_Var in LR was correlated with all four variables except the GI_Gas_Volume. When the Inhale_Rate, Lung_Volume, and BH_Duration increased, the tumor moved to the left while higher Lung_Utilization caused the tumor motion to the right.

Conclusion: Our study indicates that controlling DIBH parameters including visual-feedback of inhalation rate and minimizing variation of gastrointestinal gas volumes are important for reproducible tumor position.

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