Evaluation of Malignant Lung Tumor Motion Comparing to Fix Point during Different Respiratory Phases on Four-Dimensional Computed Tomography.

Introduction: One of the most important problems in different radiotherapy methods in lung cancer tumors is the movement of the lung during the respiratory cycle and the subsequent motion of the tumor. Changing the shape and displacement of the tumor during radiotherapy increases the radiation to the surrounding normal tissues and decreases the radiation dose to the tumor tissue. The displacement of the lung and the path of the tumor can be traced.

Methods: In an analytical study, the amount of lung tumor displacement during different phases of breathing, using four-dimensional (4D) computed tomography (CT) (4D CT) scan images in order to reduce the radiation dose to normal tissues and the maximum possible dose radiation to the target tissue, in radiotherapy treatment of lung tumors, was checked during the respiratory cycle. Also, the amount of movement of the diaphragm and tumoral tissues under the diaphragm during the respiratory cycle was estimated. Biomechanical models were used to predict the position of different parts of the lung at the end of the exhalation phase using images related to the end of the inspiratory phase.

Results: In examining the displacement of three markers in each patient, the average of displacement was 4.4 mm in the right-left (RL) direction, 6.15 mm in the anterior-posterior (AP) direction and 8.6 mm in the superior-inferior (SI) direction (P-0.001), while the average of overall displacement was 11.25 mm. Also, the difference in overall displacement was the lowest in the SI direction (2.6 mm) compared to 6.8 and 5.1 mm in the RL and AP directions, respectively.

Conclusions: By using 4D CT scan imaging it is possible to measure the exact position of the tumor in order to predict its movement pattern during the respiratory cycle, which is based on the examination and modeling of the change in position and motion of different parts of the lung and it is done using information related to respiratory dynamics.