Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Start Angle
FIELD_RADIAL_STARTANGLE
Parameter: Start Transition
FIELD_RADIAL_STARTBLEND
Parameter: End Angle
FIELD_RADIAL_ENDANGLE
Parameter: End Transition
FIELD_RADIAL_ENDBLEND
Parameter: Iterations
FIELD_RADIAL_ITERATIONS
Parameter: Offset
FIELD_RADIAL_OFFSET
Parameter: Axis
FIELD_RADIAL_AXIS
Parameter: Clip to Shape
FIELD_RADIAL_CLIP
Parameter: Offset
FIELD_RADIAL_OFFSETFIELD