What is the requirement for the door interlock (beam off)?

• A. Non-functional
• B. Functional
• C. Not required
• D. Optional during maintenance

Answer: (B)

A door interlock is a safety device that directly ensures the radiation beam is turned off whenever the treatment room door is opened. The requirement is that this interlock be functional, meaning it reliably stops the beam and places the machine in a safe state as soon as the door is opened. If the interlock isn’t functional, there’s a real risk of exposure to personnel, which is why non-functional, not required, or optional during maintenance would not meet safety standards. In practice, QA tests verify that opening the door with the beam active immediately halts radiation and that the system remains safe until the door is closed and normal conditions are restored.