Dose Course 2018_Flipping book

An alternative approach to setting Action Levels AAPM TG 218 (2018) • Preferable to use ‘universal’ action limits (correlated to outcome) • If not available then use statistical process control to determine action limits • ∆ = 2 + ( ҧ − ) 2 where ∆ is the difference between upper and lower action limits, is a factor derived from process capability and is set at 6.0 at present, 2 and ҧ are the process variance and mean. • Idea is to calculate mean and variance over eg 20 IMRT QA measurements when process is in control then use these to determine action levels.

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So it reflects what the system is capable of.