Comparison of Helical and Average Computed Tomography for Stereotactic Body Radiation Treatment Planning and Normal Tissue Contouring in Lung Cancer

Abstract

Aims To compare average computed tomography (CT AVE) datasets with free breathing helical computed tomography (CT HEL) for contouring organs at risk (OARs) and radiation treatment planning in patients receiving stereotactic body radiation therapy (SBRT) in the lung. Materials and methods Ten SBRT patients with peripheral stage I non-small cell lung cancer underwent a CT HEL and a four-dimensional computed tomography scan in the treatment position. CT AVE datasets were generated from the four-dimensional computed tomography scan. The following OARs were delineated on the CT HEL and CT AVE datasets of each patient: lung minus internal target volume, trachea/main bronchus, heart, oesophagus and spinal cord. Volumes and geometric centres of the OARs, as well as the dosimetric impact of planning with these different datasets, were examined. Results There were no statistical differences in the OAR geometric centre coordinates nor in the OAR volumes between the CT HEL and CT AVE datasets, except that CT AVE-defined trachea/main bronchus and lung minus internal target volume mean volumes were larger than those defined on the CT HEL (46, 43 cm 3 and 3516, 3378 cm 3, respectively, P < 0.05). Despite this, there were no significant differences in the mean and maximum doses to the OAR contours when using the CT HEL or CT AVE for planning (<4% average change in the maximum and mean doses for all OARs, P > 0.05). There were also no significant differences in the locations of the hotspots within OARs among the CT HEL or CT AVE datasets ( P > 0.05). Conclusions CT AVE datasets may be used in place of CT HEL for OAR contouring and dose calculations. When four-dimensional computed tomography is available, it may not be necessary to acquire a separate CT HEL scan for OAR contouring or dosimetric purposes.