TABLE II.

FBS algorithm for hybrid 4D-CBCT reconstruction.

Rigid registration from p-CT (fP) to the average 3D-CBCT image.

Repeat for each phase i (i = 0, 1, 2, …, 9)

Down-sample fP and CBCT projections gi to the coarsest resolution;

Initialize the moving vector vi to zero;

Repeat for each resolution level

While the stop criteria is not met, do

1. Calculate forward projection $P_i{f}_i^{\left(k\right)}$;

2. Reconstruct the difference image from $P_i{f}_i^{\left(k\right)}-c\left(g_i\right)$ and

get si (S1);

3. Deform $f_i^{\left(k\right)}$ toward si to obtain vi (S2 and S3);

Up-sample vi to a finer resolution level

Until the finest resolution is reached

Until all phases are done