Benefit of using motion compensated reconstructions for reducing inter-observer and intra-observer contouring variation for organs at risk in lung cancer patients

In lung cancer patients, accuracy in contouring is hampered by image artefacts introduced by respiratory motion. With the widespread introduction of 4DCT there is additional uncertainty caused by the use of different reconstruction techniques which will influence contour definition. This work aims to assess both inter- and intra-observer contour variation on average and motion compensated (mid-position) reconstructions. Eight early stage non-small cell lung cancer patients that received 4DCT were selected and these scans were reconstructed as average and motion compensated datasets. 5 observers contoured the organs at risk (trachea, oesophagus, proximal bronchial tree, heart and brachial plexus) for each patient and each reconstruction. Contours were compared against a STAPLE volume with distance to agreement metrics. Intra-observer variation was assessed by redelineation after 4 months. The inter-observer variation was significantly smaller using the motion compensated datasets for the trachea (p = 0.006) and proximal bronchial tree (p = 0.004). For intra-observer variation, a reduction in contour variation was seen across all organs at risk in using motion compensated reconstructions. This work shows that there is benefit in using motion compensated reconstructions for reducing both inter-observer and intra-observer contouring variations for organs at risk in lung cancer patients.