What is the annual TBI/TSET mode tolerance?

• A. ±1% from baseline
• B. ±2% from baseline
• C. Functional
• D. 0% tolerance

Answer: (C)

In QA practices for specialized radiation therapy modalities, some annual tolerances aren’t expressed as a fixed percent. For TBI/TSET modes, the tolerance is defined as Functional. This means the focus is on the mode being operational and deliverable as designed—the system must be able to enter and run the TBI/TSET mode, with all related hardware, software, and safety interlocks functioning properly. The exact dose-percentage limit isn’t the primary criterion here because these modes use unique setups and nonstandard dose distributions, which don’t lend themselves to a single universal percent tolerance. If the mode can be selected, can deliver, and remains safe and reproducible, the annual tolerance is considered met.