Final answer:
The question pertains to daily QA procedures on a linac in radiation therapy. Of the listed options, door interlocks are the feature that may not be checked daily as part of standard QA procedures unless institutional protocols dictate otherwise.
Step-by-step explanation:
The subject of the question is concerned with daily quality assurance (QA) procedures that must be performed on a linear accelerator (linac), which is used in radiation therapy for treating cancer patients.
Among the options provided, daily QA checks include X-ray and electron output constancy, light/radiation field coincidence, and ODI accuracy. However, checking the door interlock is a safety feature that might not necessarily be checked daily unless specified by particular institutional protocols or after maintenance activities.