Table 1.

Verification techniques and methodologies for patient specific IMRT QA in China

Items				Number	Percentage (%)
Techniques	Point dose	Tools	Ion chamber	331	82.1
	2D dose	Tools	2D diode or chamber arrays	348	86.4
			EPID	78	19.4
			Film + diode or ionization chamber arrays	58	14.4
			Film	12	3.0
	3D dose	Tools	ArcCheck or Delta 4	52	12.9
Methodologies	Point dose	Location of ion chamber	Isocenter	198	49.1
			Maximum dose point	67	16.6
			Uniform high dose region	39	9.7
			Isocenter or a uniform high dose region	42	10.4
			5 cm for 6 MV, 10 cm for 10 MV plans	29	7.2
		Measurement value	Mean dose to ion chamber volume	171	42.4
			Point dose (effective measurement point)	172	42.7
		Tolerance limits	2%	3	0.7
			3%	356	88.3
			4%	1	0.2
			5%	21	5.2
			Other	19	4.7
			No response	17	4.2
		Action limits	2%	35	8.2
			3%	154	38.2
			5%	78	19.4
			10%	1	0.2
			Other	20	5.0
			No response	161	40
	2D, 3D dose	Delivery methods	Perpendicular field-by-field (PFF)	190	47.1
			Perpendicular composite (PC)	258	64.0
			True composite (TC)	110	27.3
			PFF after PC failure	107	26.6
		Orientation of film/array	Coronal	340	84.4
			Sagittal	35	8.7
			Transverse	41	10.2
		Absolute dose calibration	Before each IMRT QA session	115	28.5
			Weekly	84	20.8
			Monthly	128	31.8
			Every 3 months to one year	70	17.4
			Never	3	0.7
		Grid size	1 mm	39	9.7
			2 mm	155	38.5
			2.5 mm	50	12.4
			3 mm	190	47.1
			4 mm	67	16.6
			5 mm	2	0.5
			Varied with TPS, delivery techniques	75	18.6
		Reference distribution	Measured dose	205	50.9
			Calculated dose	282	70.0
		Dose algorithm	Pencil beam	108	26.8
			Convolution/and superposition	278	69.0
			Monte Carlo	140	34.7
		Evaluation metrics	Dose difference (DD) at multiple points	168	41.7
			Distance-to-agreement (DTA),	155	38.5
			Gamma pass rate	353	87.6
			Profiles or isodose distributions	157	39.0
			Anatomy-based 3D dose distributions and DVHs	20	5.0
		Tolerance limits	90%	38	9.4
			95%	293	72.7
			93%	1	0.2
			No response	85	21.1
		Action limits	90%	35	8.7
			95%	262	65.0
			80%	2	0.5
			No response	118	29.3
		Gamma criteria	2% DD	35	8.7
			3% DD	305	75.7
			4% DD	17	4.2
			5% DD	57	14.1
			1 mm DTA	8	2.0
			2 mm DTA	50	12.4
			3 mm DTA	300	74.7
			4 mm DTA	15	3.7
			5 mm DTA	1	0.2
		Normalization point	Maximum dose point	207	51.4
			Isocenter	166	41.2
			Other points in the high dose plateau region	80	19.9
		Normalization modes	Global normalization	306	75.9
			Local normalization	78	19.4
		Dose analysis modes	Absolute	225	55.8
			Relative	235	58.3
			Both	85	21.1
		Dose thresholds	10%	286	71.0
			20%	33	8.2
			5% or 15%	38	9.4
Reasons and actions		Reasons for failed QA	Plan being too highly modulated	287	71.2
			Dose measurement point in a high gradient region	232	57.6
			Inaccurate phantom set up	195	48.4
			MLC positioning uncertainty	201	49.9
		Actions for failed QA	Checking the verification plan	296	73.4
			Checking the VS, TPS and delivery system	353	87.6
			Re-measure or design verification plan again	317	78.7
			Previous plan verification	151	37.5
			Communicated with physicians	146	36.2
			Re-plan	199	49.4
MLC QA		Frequency	Monthly	242	60.0
			Weekly	131	32.5
			Daily	66	16.4
			Every season, half year or one year	53	13.2
			Never	33	8.2
Audits and clinical trial		Type	External audits or inter-institution comparison	168	41.7
			Clinical trial credential	13	3.2
Issues of IMRT QA		Type	Lack of physicists	174	43.2
			Lack of time	230	57.1
			Lack of QA devices	196	48.6
			Lack of linacs	182	45.2