Table 2.
Summary of nine registration techniques explored in this study. The nominal techniques provide a lower bound on LE for each metric. As such, it is unnecessary to compute border LE for centroid alignment and centroid LE for border alignment. Therefore, only eight registration techniques are presented for each LE metric in the remaining tables and in Figs. 3456. NMI: normalized mutual information.
| Registration | Short name | Description | Implementation |
|---|---|---|---|
| Bony-anatomy | Bony | Manual alignment of the spine, sternum, and ribs using translations and rotations. All other registrations use translational degrees of freedom only | Manual |
| Standard NMI | Standard | Direct, automatic registration of lung cancer targets, including the primary tumor and/or involved lymph nodes, between on-treatment and planning images | Automatic |
| Seeded NMI | Seeded | Quick, approximate manual prealignment of targets, followed by standard registration | Semi-automatic |
| Intermediate transitive-based | Intermediate-TB | Alignment of on-treatment and planning images by composing the separate registrations of each to a single intermediate image [Eq. 2] | Automatic |
| Consecutive transitive-based | Consecutive-TB | Alignment of on-treatment and planning images by composing the separate registrations between all consecutive weekly images [Eq. 3] | Automatic |
| Intermediate rereferenced | Intermediate-RR | Designation of a single, intermediate weekly CT as the new reference for registration of all subsequent treatment fractions, given that the relative orientation is known between the new reference and planning images [Eq. 4] | Semi-automatic |
| Consecutive rereferenced | Consecutive-RR | Designation of the previous weekly CT as the new reference for registration of the current on-treatment image, given that the relative orientation is known between the new reference and planning images [Eq. 5] | Semi-automatic |
| Nominal centroid alignment | Centroid | Registration to minimize centroid localization errors for all targets simultaneously | Computed from target contours |
| Nominal border alignment | Border | Registration to minimize the distance between reference and secondary target borders in the left–right, anterior–posterior, and superior–inferior directions, computed directly from the manual contours | Computed from target contours |