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Table 1 Verification techniques and methodologies for patient specific IMRT QA in China

From: National survey of patient specific IMRT quality assurance 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