Table 1.

Comparison of the three main methods for mechanical isocenter verification.

Method	Advantages	Disadvantages
Mechanical pointer	Does not require programming or special devices.	Manual, laborious. Time‐consuming. Observer‐dependent. Large measurement uncertainties.
Film based W‐L test	Better accuracy than pointer. Easy phantom setup. Semi‐automatic.	Only few angles can be tested. Requires film setup and processing. Nondigital data. No contrast enhancement. Observer‐dependent.
EPID based W‐L test	Digital images. Quick setup. Contrast enhancement. Automatic. Require lower radiation than films.	Impossible at certain gantry and couch angles. Lower resolution than films.