Table 4. 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	121	81	64	25	36
Whether found cylinder that drilling is available	✓	✓	✓	✓	✓
Average Hounsfield value	700.8	760.7	804.9	549.6	436.1
Time complexity	188	127	92.8	80.6	57.1