4DCT-based evaluation of lung tumour motion during the breathing cycle.

The aim of this work was to quantify the variability in pre-treatment lung tumor motion during a single breathing period for 55 non-small cell lung cancer (NSCLC) targets. The influence of breathing on the volume and position of lung tumor was examined by comparing the information about tumor from respiratory-correlated four-dimensional computed tomography (4DCT) and three-dimensional computed tomography (3DCT) obtained without respiratory monitoring. The impact of age, gender, lung volume changes and immobilization device on tumor respiratory motion was evaluated. Based on the performed analysis, the significant differences were found between tumor volumes on 3DCT and 4DCT, although the comparison of volumes between 4DCT bins showed no statistically significant dependency. The significant differences between tumor centre of mass coordinates in the cranial-caudal (CC) and anterior-posterior (AP) directions were found. According to the results of statistical testing, there was no impact of gender and immobilization device on detected tumor respiratory motion. The impact was found for patient's age, lung volume changes, tumor volume and its location in different lung segments. The dominant lung cancer motion was observed for smaller tumors (up to 20 cc) located in posterior, caudal segments. This effect was also associated with a large variation in the lung volume during one respiratory cycle, observed for older patients. The important finding of the study is connected with the description of different patterns of tumor motion in AP and CC directions.