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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