What is the monthly typical dose rate output constancy tolerance?

• A. 1%
• B. 1.5%
• C. 2% (stereotactic dose rate, MU)
• D. 3%

Answer: (C)

The key idea is how much the machine’s dose rate can drift from its baseline on a monthly check. In routine QA, the typical tolerance for dose rate output constancy is about 2%. That means the measured dose rate should stay within ±2% of the reference value across monthly checks.

For stereotactic dose rate checks, when the measurement is expressed in monitor units (MU), the same 2% tolerance applies because the high precision required in SRS/SBRT calls for keeping the output tight, even though the quantity is MU-based.

Choosing a tighter value like 1% or 1.5% would be more stringent than standard practice, while 3% would be looser than typical guidelines.