The effect on dose accumulation accuracy of inverse-consistency and transitivity error reduced deformation maps

It has previously been shown that deformable image registrations (DIRs) often result in deformation maps that are neither inverse-consistent nor transitive, and that the dose accumulation based on these deformation maps can be inconsistent if different image pathways are used for dose accumulation. A method presented to reduce inverse consistency and transitivity errors has been shown to result in more consistent dose accumulation, regardless of the image pathway selected for dose accumulation. The present study investigates the effect on the dose accumulation accuracy of deformation maps processed to reduce inverse consistency and transitivity errors. A set of lung 4DCT phases were analysed, consisting of four images on which a dose grid was created. Dose to 75 corresponding anatomical locations was manually tracked. Dose accumulation was performed between all image sets with Demons derived deformation maps as well as deformation maps processed to reduce inverse consistency and transitivity errors. The ground truth accumulated dose was then compared with the accumulated dose derived from DIR. Two dose accumulation image pathways were considered. The post-processing method to reduce inverse consistency and transitivity errors had minimal effect on the dose accumulation accuracy. There was a statistically significant improvement in dose accumulation accuracy for one pathway, but for the other pathway there was no statistically significant difference. A post-processing technique to reduce inverse consistency and transitivity errors has a positive, yet minimal effect on the dose accumulation accuracy. Thus the post-processing technique improves consistency of dose accumulation with minimal effect on dose accumulation accuracy.