How Regular Motion Pattern and Patient Individual Respiration Curves Affect Contour and Volume of Geometric Structures in a 4D CT

Abstract

In our previous studies, we have reported on the methodology and feasibility of respiration gated radiotherapy, to reduce margins and lower side effects. A prerequisite for planning gated radiotherapy is a 4D CT. Using a motorized phantom for regular motion pattern we worked out a quality assurance procedure to take into account the special features for moving objects in a 4D CT. In this study, we expand our investigation to address the problem of irregular motion in CT imaging. A 4D CT acquisition was performed using a "step-and-shoot" technique, in which computed tomography (CT) projection data were acquired over a complete respiratory cycle at each coach position. 4D CT data were then sorted into 10 groups, according to their corresponding phase of the breathing cycle. The effect of motion on automatic contouring the patient outline and target volume and the volume change were investigated. Also the influences of regular motion pattern and patient individual respiratory trace on the clinical target volume were compared. The use of respiratory gating will potentially improve radiotherapy outcomes by allowing reduced treatment margins. Treating patients using gating requires several clinical decisions on the basis of exact information’s about the internal target motion and the correlation to an external surrogator. Therefore knowledge how an irregular respiration pattern under gating conditions influences target size and shape are of extraordinary importance.