Table 3. When the angle between the drill and vertical axis is less than or equal to 20°.

Drill radius (mm)	2	2.5	3	3.5	4
Numbers of checked cylinders	81	49	36	25	25
Whether found cylinder that drilling is available	✓	✓	✓	✓	✓
Average Hounsfield value	716.9	760.7	815.4	583.8	550.8
Time complexity	128	75.3	48.9	39.9	38.1