TU‐C‐303A‐06: Quiet Respiration Breathing Motion Model Parameters for Free‐Breathing Patients

Purpose: To determine the quiet respiration breathing motion model parameters for lung cancer and non‐lung cancer patients. Method and Materials: 49 free‐breathing patient 4DCT image data sets (25 scans, ciné mode) were collected with simultaneous quantitative spirometry. A cross‐correlation registration technique was employed to track the lung tissue motion between scans. The registration results were fed back to a lung‐motion model: [formula omitted], where x is the position of a piece of tissue located at reference position x₀. α is a parameter which characterizes the motion due to local air filling (motion as a function of tidal volume) and β is the parameter that accounts for the motion due to the imbalance of dynamical stress distributions during inspiration and exhalation which cause lung motion hysteresis (motion as a function of airflow). The parameters α and β together provide a quantitative characterization of breathing motion that inherently includes the complex hysteresis interplay. The α and β distributions were examined for each patient to determine overall general patterns and intra‐patient pattern variations. Results: For 44 patients, the greatest value of |α| was observed in the inferior and posterior lungs. In three patients, |α| reached its maximum in the anterior lung, while for two patients; |α| was greatest in the lateral lung. The hysteresis motion β had greater variability, but for the majority of patients, |β| was largest in the lateral lungs. Conclusion: This is the first report of the 3‐dimensional breathing motion model parameter for a large cohort of patients. The overall α and β maps varied smoothly as expected. The majority of patients exhibited consistent α maps, and the β maps showed greater intra‐patient variability. The motion parameter intra‐patient variability will inform our need for custom radiation therapy motion models.