Artifact in CBCT Sart reconstruction

Hello, when I use more than 180 projections (e.g., 250 projections) to reconstruct CBCT, severe streak artifacts appear.

When I used fewer projection views such as 100, I did not find this bar artifact.

## Geometry
geo.DSD = 1502.19 # Distance Source Detector (mm)
geo.DSO = 1161.91 # Distance Source Origin (mm)
geo.nDetector = np.array([1536, 1536]) # number of pixels (px)
geo.dDetector = np.array([ 0.278, 0.278]) # size of each pixel (mm)
geo.sDetector = geo.nDetector * geo.dDetector # total size of the detector (mm)
geo.nVoxel = np.array([512,512,512]) # number of voxels (vx)
geo.dVoxel = np.array([0.6, 0.6, 0.6]) # size of each voxel
geo.sVoxel =geo.nVoxel * geo.dVoxel # total size of the image (mm)
geo.offOrigin = np.array([0, 0, 0]) # Offset of image from origin (mm)
geo.offDetector = np.array([0, 0]) # Offset of Detector (mm)
geo.accuracy = 0.5 # Variable to define accuracy o
geo.COR = 0
#geo.rotDetector = np.array([0, 0, 0]) # Rotation of the detector, by
geo.mode = "cone" # Or 'parallel'. Geometry type.
lmbda = 1
lambdared = 0.999
initmode = None
verbose = True
qualmeas = ["RMSE", "SSD"]