Use of statistical process control to study the patient-specific quality assurance in head and neck cancer

Table 1 Control limits, tolerance limits, and action limits for Individual-chart and Exponentially Weighted Moving Average analysis of patient-specific quality assurance gamma passing rates in head-and-neck radiotherapy plans across four gamma criteria (3%/3 mm, 2%/3 mm, 3%/2 mm, and 2%/2 mm)

Criteria	Individual charts			Moving-range charts			Exponentially Weighted Moving Average charts			Tolerance limit	Action limit
	Upper control limit	Central line	Lower control limit	Upper control limit	Central line	Lower control limit	Upper control limit	Central line	Lower control limit
3%, 3 mm	99.801	98.835	97.869	1.187	0.363	0	99.1569	98.835	98.5131	97.8694	96.4844
3%, 2 mm	98.437	97.415	96.393	1.255	0.384	0	97.7556	97.415	97.0744	96.3936	92.2299
2%, 3 mm	96.5	95.59	94.68	1.118	0.342	0	95.8933	95.59	95.2867	94.6803	86.7638
2%, 2 mm	95.128	94.4	93.672	0.894	0.274	0	94.6426	94.4	94.1574	93.6712	83.1989