Machine-specific QC in Aarhus using EPID

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Machine-specific QC in Aarhus using EPID

• Mai-Britt K. Jørgensen, Lone Hoffmann, L.P.
  Muren, Lars H. Præstegaard, Rune Hansen, Jørgen
  B.B. Pedersen, Maria F. Jensen
• Aarhus University Hospital
• Department of Medical Physics

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Rutine QC
IMRT VMAT
Machine specific Sweeping gap Picket fence (PF) Sweeping gap Picket fence (PF) Dose rate versus gantry speed (DRGS) Dose rate versus MLC speed (DRMLC)
Patient specific PDI (Delta4) (PTW729 array) PDI (Delta4)
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Picket fence, PF

• For every MLC and gab
• Position
• Relative rotation of EPID and collimator
• Intensity (width)

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PF ex. Eye test
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PF ex. Deviation in position, tolerance 0.3mm
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PF ex. Deviation in intensity, tolerance 300
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PF ex. Eye test version 2
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PF In total 30 test on each accelerator, one
every month
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Dose rate vs. gantry speed, DRGS
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DRGS ex. typical deviation
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DRGS ex. cable issue
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DRGS In total 30 test on each accelerator, one
every month
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Dose rate vs. MLC speed, DRMLC
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DRMLC ex. segment 4 DR120, 0.4cm/s
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DRMLC ex. segment 2 DR600, 2.4cm/s
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DRMLC ex. segment 4 DR120, 0.4cm/s segment
1 DR480, 1.6cm/s
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DRMLC In total 30 test on each accelerator, one
every month
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Time consumption

• Measurements 10 min
• Analysis (home-made software) 1 min
• Total 11 min

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Effect of chain adjustments on the DRGS and DRMLC
tests

• Mehtod
• 3 DRGS and 3 DRMLC test with a loose chain
• 3 DRGS and 3 DRMLC test with a thight chain
• Result, comparing loose and thight chain
• DRGS Standard deviation was unchanged
• DRMLC Std 0.6 (loose) -gt 0.2 (tight)

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Loose chain unstable characteristic
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Tight chain Stable characteristic
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Discussion

• Deviations in PF are covered in next, next
  session
• Deviations in DRGS and DRMLC
• Chain adjustments have an effect on DRGS and
  DRMLC test, but it does not solve everything
• Cable issues
• Beam adjustments?
• For more information on the calculations and
  tolerances
• Med. Phys. 38, 1425 (2011)